Measurement Challenges of Nitrogen Species in ... - ACS Publications

9

Downloaded via UNIV OF CALIFORNIA SANTA BARBARA on September 24, 2018 at 04:35:32 (UTC). See https://pubs.acs.org/sharingguidelines for options on how to legitimately share published articles.

Measurement Challenges of Nitrogen Species in the Atmosphere D a v i d D. Parrish and M a r t i n P. Buhr 1

1

2

1,2

Aeronomy Laboratory, National Oceanic and Atmospheric Administration, Boulder, CO 80303 Cooperative Institute for Research in Environmental Sciences, University of Colorado, Boulder, CO 80309

Understanding the chemistry and physics of atmospheric nitrogen species presents several challenges for analytical chemists; these chal lenges are discussed in the context of an overview of measurement techniques and recent results from field studies. In the troposphere, reliable in situ techniques to measure HNO , organic nitrates, NO , N O , and HONΟ are required, and fast response (1 to 10 Hz) tech niques are needed to measure the surface fluxes of N O, NH , NO , and HNO by micrometeorological techniques. In the stratosphere, fast response (about 1 Hz) instruments are required for in situ mea surements of NO , N O , HNO , ClONO , and HO NO from aircraft. In the troposphere and stratosphere, instruments to characterize aerosols must be developed. These instruments must be integrated into packages for surface and aircraft studies that simultaneously measure a wide range of atmospheric species, and these packages must be deployed in field studies to elucidate atmospheric processes and to define the spatial and temporal distributions of the atmo spheric nitrogen species. 3

2

3

5

2

3

2

3

2

2

5

3

2

2

2

SOCIETY IS FACING SEVERAL CRUCIAL ISSUES

involving atmospheric c h e m istry. Species c o n t a i n i n g n i t r o g e n are major players i n each. I n the t r o p o sphere, n i t r o g e n species are catalysts i n the p h o t o c h e m i c a l cycles that f o r m ozone, a major u r b a n a n d r u r a l p o l l u t a n t , as w e l l as o t h e r oxidants (references 1 a n d 2, a n d references c i t e d therein), a n d t h e y are i n v o l v e d i n a c i d p r e c i p i t a t i o n , b o t h as one of the t w o major acids (nitric acid) a n d as a base (ammonia) (3, 4). I n the stratosphere, w h e r e ozone acts as a s h i e l d for t h e 0065-2393/93/0232-0243$08.75/0 © 1993 American Chemical Society

Newman; Measurement Challenges in Atmospheric Chemistry Advances in Chemistry; American Chemical Society: Washington, DC, 1993.

244

MEASUREMENT CHALLENGES IN ATMOSPHERIC CHEMISTRY

e a r t h from the sun's harsh ultraviolet r a d i a t i o n , n i t r o g e n species p l a y several roles i n the ozone d e s t r u c t i o n cycles that threaten to r e d u c e that s h i e l d (reference 5 a n d references c i t e d therein). O z o n e , as w e l l as one m e m b e r of the n i t r o g e n f a m i l y , N 0 , are " g r e e n h o u s e " gases, w h i c h t h r e a t e n to i n d u c e climate change t h r o u g h atmospheric w a r m i n g (reference 6 a n d references c i t e d therein). T h u s , the d i s t r i b u t i o n s of the n i t r o g e n species must be w e l l k n o w n to u n d e r s t a n d these i m p o r t a n t issues. 2

T h e n i t r o g e n species e n t e r the atmosphere from a v a r i e t y of n a t u r a l a n d anthropogenic sources (7). T h e largest sources are concentrated i n u r b a n a n d i n d u s t r i a l i z e d areas. T h e levels of the species i n the atmosphere v a r y from h u n d r e d s of parts p e r b i l l i o n b y v o l u m e (ppbv, that is, 10~ m o l e fraction) i n these source regions to b e l o w one part p e r t r i l l i o n b y v o l u m e (pptrv, 1 0 " m o l e fraction) i n r e m o t e areas. E v e n at the p p t r v l e v e l , these species can p l a y significant roles i n atmospheric c h e m i s t r y , a n d m e a s u r e ments of species at the s u b - p p t r v l e v e l can y i e l d useful i n f o r m a t i o n c o n c e r n i n g atmospheric p h o t o c h e m i s t r y . 9

12

Atmospheric nitrogen species—both characterized and uncharacteri z e d — i n c l u d e nearly a l l oxidation states of n i t r o g e n a n d encompass a large n u m b e r of distinct molecules. W i t h the c r u c i a l roles these species p l a y , the l o w concentrations of interest, the w i d e d y n a m i c range of concentrations e n c o u n t e r e d , a n d the w i d e variety of species i n c l u d e d i n this f a m i l y , anal y t i c a l chemists face m a n y challenges i n the d e v e l o p m e n t of i n s t r u m e n t a t i o n for c h a r a c t e r i z i n g the atmospheric n i t r o g e n family. T h e d e v e l o p m e n t of i n s t r u m e n t a t i o n is o n l y the first step. T h e d e p l o y m e n t of the i n s t r u m e n t a t i o n i n p i o n e e r i n g field studies is a second challenge. A t m o s p h e r i c c h e m i s t r y is a n e w e n o u g h field, a n d the i n s t r u m e n t a l c h a l lenges are great e n o u g h , that progress is still l i m i t e d b y data. E v e r y n e w advance i n i n s t r u m e n t a t i o n d e p l o y e d i n a w e l l - p l a n n e d field study can b r i n g e x c i t i n g n e w insights i n t o the c o n t r o l l i n g processes of a t m o s p h e r i c c h e m i s t r y . T h e concentration of each n i t r o g e n species exhibits systematic variations w i t h l a t i t u d e , l o n g i t u d e , a n d altitude. T h e concentration at each location i n the atmosphere w i l l usually e x h i b i t d i u r n a l a n d seasonal cycles as w e l l as l o n g - t e r m trends. S u p e r i m p o s e d o n these systematic variations are m o r e i r r e g u l a r changes that reflect the history of the p a r t i c u l a r air p a r c e l transp o r t e d to the location. T h u s , there is the m u n d a n e b u t d a u n t i n g challenge of c h a r a c t e r i z i n g these variations for each of the species b y field studies i n c o r p o r a t i n g l o n g - t e r m m o n i t o r i n g . F o r t u n a t e l y there are l o c a l , r e g i o n a l , a n d global c o m p u t e r m o d e l s i n various stages of d e v e l o p m e n t that seek to p r e d i c t these variations. U l t i m a t e l y it s h o u l d be possible to r e l y o n the results of these m o d e l s to m i n i m i z e the r o u t i n e m o n i t o r i n g r e q u i r e m e n t s , b u t c u r r e n t l y field measurements are n e e d e d to validate the results of the c o m p u t e r models. A p a r t i c u l a r l y fruitful interaction exists b e t w e e n the e x p e r i m e n t a l i s t a n d the m o d e l e r . T h e experimentalist makes p i o n e e r i n g field m e a s u r e m e n t s that


9.

PARRISH & B U H R

Measurement Challenges of Nitrogen Species

245

g u i d e the m o d e l e r i n selecting the i m p o r t a n t c h e m i c a l species a n d reactions to i n c l u d e i n the d e v e l o p i n g m o d e l , a n d the sensitivity of the m o d e l results to p a r t i c u l a r parameters guides the e x p e r i m e n t a l i s t i n p l a n n i n g fruitful f i e l d and laboratory k i n e t i c studies. S e v e r a l examples of c o m p u t e r m o d e l results and h o w this i n t e r a c t i o n operates are discussed. T h i s chapter focuses o n several specific c u r r e n t challenges i n the m e a s u r e m e n t of the n i t r o g e n species. E x a m p l e s of past results are i n c l u d e d to give an i n d i c a t i o n of the insights into a t m o s p h e r i c processes that are p o t e n tially realizable f r o m f i e l d studies. M a n y laboratories a r o u n d the w o r l d are i n v o l v e d i n these studies. T h e examples are d r a w n d i s p r o p o r t i o n a t e l y f r o m our laboratory s i m p l y for c o n v e n i e n c e . A l t h o u g h other examples can b e c i t e d , the ones i n c l u d e d here are to a great extent representative of the field's results. A n i n t r o d u c t i o n to the species c o m p o s i n g the a t m o s p h e r i c n i t r o g e n f a m ily is f o l l o w e d b y a discussion of the specific goals of the m e a s u r e m e n t s . A survey of the general approaches to these m e a s u r e m e n t s a n d a d e s c r i p t i o n of m e a s u r e m e n t platforms completes the i n t r o d u c t o r y m a t e r i a l . A n o u t l i n e of the g e n e r a l challenges that are e n c o u n t e r e d i n m a k i n g s u c h m e a s u r e m e n t s and descriptions of specific challenges that are p a r t i c u l a r l y i m p o r t a n t to the atmospheric c h e m i s t r y c o m m u n i t y at the present t i m e c o m p l e t e the chapter.

Atmospheric Nitrogen Species T h e p r i m a r y sources that are responsible for the presence of this f a m i l y of c o m p o u n d s i n the atmosphere e m i t N H , N 0 , a n d N O to the t r o p o s p h e r e , the lowest l e v e l of the atmosphere, w h i c h extends to a p p r o x i m a t e l y 10 k m from the earth's surface. N H seems to u n d e r g o v e r y little c h e m i s t r y i n the atmosphere except for the formation of aerosols, i n c l u d i n g a m m o n i u m nitrate and sulfates. N H a n d the aerosols are h i g h l y soluble a n d are thus r a p i d l y r e m o v e d b y p r e c i p i t a t i o n a n d d e p o s i t i o n to surfaces. N 0 is u n r e a c t i v e i n the troposphere. O n a t i m e scale of decades it is t r a n s p o r t e d to the strato sphere, the next h i g h e r a t m o s p h e r i c layer, w h i c h extends to about 50 k m . H e r e N 0 e i t h e r is photodissociated or reacts w i t h e x c i t e d oxygen atoms, Ο ( D). T h e final products from these processes are p r i m a r i l y u n r e a c t i v e N and 0 , b u t about 1 0 % N O is also p r o d u c e d . T h e p r o d u c t N O is the p r i n c i p a l source of reactive o x i d i z e d n i t r o g e n species i n the stratosphere. 3

2

3

3

2

2

1

2

2

N O initiates the r a p i d p h o t o c h e m i s t r y b o t h i n the t r o p o s p h e r e a n d i n the stratosphere that produces the majority of the f a m i l y m e m b e r s . A s the n i t r o g e n is o x i d i z e d f u r t h e r , the m a n i f o l d of species s h o w n i n F i g u r e 1 is f o r m e d . T h e s e i n c l u d e the l i s t e d inorganic species a n d , i n regions w h e r e n o n m e t h a n e hydrocarbons are also present, organic nitrates. T h e most i m portant organic nitrate is P A N , p e r o x y a c e t y l n i t r a t e , w i t h the f o r m u l a C H C ( 0 ) 0 N 0 ; o t h e r p e r o x y a c y l nitrates a n d a l k y l nitrates are also k n o w n . T h e r e is e v i d e n c e that other n i t r o g e n - c o n t a i n i n g organic species, a n d p e r 3

2

2


246

M E A S U R E M E N T C H A L L E N G E S IN ATMOSPHERIC

CHEMISTRY

Figure 1. Reactive oxidized nitrogen species present in the atmosphere. R represents single- or multifunctional organic groups. (Reproduced with permission from reference 57. Copyright 1990 Pergainon Press.)

haps other inorganic species, are p r e s e n t l y u n d e t e c t e d ; these species c o m plete the family. T w o t e r m s are c o m m o n l y used i n the field to c o l l e c t i v e l y refer to these species. N O represents the s u m of N O p l u s N 0 . T h e s e two species are c o m b i n e d i n one t e r m because t h e y are i n t e r c o n v e r t e d i n the s u n l i t a t m o sphere o n a t i m e scale of a p p r o x i m a t e l y 1 m i n , so t h e i r s u m is a m o r e c o n s e r v e d q u a n t i t y than is e i t h e r separately. H o w e v e r , no t e c h n i q u e c u r r e n t l y exists for d i r e c t l y m e a s u r i n g the s u m of the N O a n d N 0 c o n c e n t r a tions; each m u s t be d e t e r m i n e d separately. N O , w h i c h can b e r e f e r r e d to as total reactive o x i d i z e d n i t r o g e n , represents the s u m of the species that have n i t r o g e n i n an oxidation state of + 2 or h i g h e r . H o w e v e r , t e c h n i q u e s have b e e n d e v e l o p e d that are b e l i e v e d to measure the c o m p l e t e f a m i l y concentration of at least the gaseous species i n a single d e t e r m i n a t i o n . v

2

2

? /

Goals of the Measurements In essence, measurements of these n i t r o g e n species are r e q u i r e d to u n d e r stand the several b i o g e o c h e m i c a l cycles that transport m a t e r i a l t h r o u g h the


9.

PARRISH & B U H R


247

atmosphere. S e v e r a l specific goals can b e i d e n t i f i e d . F i r s t , as discussed i n the i n t r o d u c t i o n , these species are so i n t i m a t e l y i n v o l v e d i n a t m o s p h e r i c p h o t o c h e m i s t r y that the spatial a n d t e m p o r a l d i s t r i b u t i o n s of t h e i r c o n c e n trations m u s t b e k n o w n to b e g i n to d e v e l o p a clear p i c t u r e of the a t m o s p h e r i c processes. S e c o n d , it is also i m p o r t a n t to quantify the fluxes of these species b e t w e e n the surface a n d the atmosphere a n d w i t h i n the a t m o s p h e r e . I f the a t m o s p h e r i c concentrations a n d rates of transformation processes are k n o w n , t h e n t h e y can be c o m b i n e d w i t h the fluxes to d e v e l o p a closed b u d g e t for a g i v e n a t m o s p h e r i c species. D e t e r m i n a t i o n o f the fluxes r e q u i r e s m e a s u r e m e n t of the concentrations of the species a n d of c o n c u r r e n t m e t e o r o l o g i c a l parameters. T h i r d , a n d perhaps most i n t e r e s t i n g , i f these species are m e a s u r e d i n w e l l - d e s i g n e d studies, p h o t o c h e m i c a l relationships can b e e x a m i n e d that p r o v i d e d i r e c t tests of o u r u n d e r s t a n d i n g of the processes of a t m o s p h e r i c chemistry. T w o examples serve to illustrate these p h o t o c h e m i c a l r e l a t i o n s h i p s . O n e m e m b e r o f the f a m i l y of atmospheric peroxy radicals is the p e r o x y acetyl radical, C H C ( 0 ) 0 . I n at least the w a r m p o r t i o n o f the t r o p o s p h e r e , P A N is near t h e r m a l e q u i l i b r i u m w i t h the peroxy acetyl radical a n d N O . T h e e q u i l i b r i u m constant for this reaction has b e e n m e a s u r e d i n laboratory s t u d ies. T h e r e f o r e , i f concentrations of b o t h P A N a n d N 0 are m e a s u r e d , the concentration of these radicals can be calculated f r o m the e q u i l i b r i u m c o n stant a n d the ratio of the two n i t r o g e n species as s h o w n i n F i g u r e 2. T h e 3

2

£

2

30 CH C(0)0 N0 3

K > Φ·* α

e q

=

2

4.2 Χ

2

CH C(0)0 3

2

+ Ν0

1027 e x p ( - 1 3 5 0 0 / T ) f

2

cm-3

20

CM Ο ο Χ ο

101

7/4

7/5

7/6

7/7

Figure 2. Peroxy acetyl radical equilibrium chemistry and concentrations de rived for a 4-day period dunng afield study in rural Pennsylvania. The two curves give model predicted concentrations for two different scenarios. (Adapted with permission from reference 8. Copyright 1991 American Geo physical Union.)

American Ctemicai Society Library 1155 16th SUHW. Newman; Measurement Challenges in Atmospheric Chemistry Advances in Chemistry; American Chemical O.C. Society: Washington, DC, 1993. Washington, 200B

248


data points show the i n f e r r e d peroxy acetyl radical concentrations, a n d the lines are a p h o t o c h e m i c a l m o d e l calculation for two different scenarios (8). T h u s , m o r e i n f o r m a t i o n c o n c e r n i n g the atmosphere has b e e n g a i n e d t h a n s i m p l y the concentrations of the two n i t r o g e n species. F u r t h e r m o r e , a c r i t i c a l test of the m o d e l results is possible. I n a d d i t i o n , the b e h a v i o r of the i n f e r r e d concentration of the radicals can be evaluated for reasonableness. Because the radicals are p r o d u c e d f r o m r e l a t i v e l y r a p i d reactions i n i t i a t e d b y p h o tolysis, t h e i r concentration is expected to d r o p at n i g h t . T h e results follow this expectation a n d give the investigators confidence i n the v a l i d i t y of t h e i r measurements. A n o t h e r example of a p h o t o c h e m i c a l r e l a t i o n s h i p is i n the a l k y l n i t r a t e , R O N 0 , c h e m i s t r y . T h e a l k y l nitrates are f o r m e d i n the atmosphere d u r i n g the oxidation of hydrocarbons (outlined i n F i g u r e 3). T h e r a t e - d e t e r m i n i n g step of the oxidation is attack b y a h y d r o x y l radical, w h i c h extracts a h y d r o g e n atom from the h y d r o c a r b o n to y i e l d the a l k y l radical. T h e a l k y l radical q u i c k l y c o m b i n e s w i t h 0 to give the peroxy radical. T h i s radical t h e n reacts w i t h N O (usually b y transferring an oxygen atom to oxidize it to N 0 ) a n d leaves the oxy radical, w h i c h t h e n goes o n to f o r m an a l d e h y d e o r ketone. H o w e v e r , there is some p r o b a b i l i t y , a , that the p e r o x y radical s i m p l y c o m b i n e s w i t h the N O to give the a l k y l nitrate. T h e p r o b a b i l i t y of f o r m i n g an a l k y l nitrate varies from about 0.08 for a C peroxy radical to about 0.30 for a C peroxy radical (9). T h e a l k y l nitrate is r e m o v e d f r o m the atmosphere b y p h o t o d i s sociation (at the l i g h t - d e p e n d e n t photolysis rate /) or oxidation b y a h y d r o x y l radical. T h e s e r e m o v a l reactions are slow, so this reaction sequence can be 2

2

2

2

8

0

OH

RH

R

Γ

2

R0

Ί

2

hZ/,OH| PRODUCTSKj

More simply: RHç4>aR0N0, 2

RONO products v.g- J + y o H i 2

k » A

k ÏÔHÏ 1

k

Figure 3. Alkyl nitrate chemistry and kinetics.


9.

PARRISH & B U H R


249

s i m p l i f i e d to two s e q u e n t i a l pseudo-first-order reactions. T h e rate constants, k a n d k , are r e l a t e d to the rate constants for the h y d r o x y l radical reactions and to the d i u r n a l averages of the h y d r o x y l radical c o n c e n t r a t i o n a n d p h o tolysis rate. T w o s e q u e n t i a l first-order reactions constitute a c o m m o n k i n e t i c s example h a n d l e d i n undergraduate p h y s i c a l c h e m i s t r y , a n d the t i m e e v o l u t i o n of the ratio of the a l k y l nitrate to the p a r e n t alkane can b e i n t e g r a t e d to y i e l d A

B

[ R O N 0 ] / [ R H ] = [akJ(k 2

B

- * )][1 - «f N H ( b i £ ) + p r o d u c t s +

N H ( b * £ \ v"=0) + h u

2

N H ( C % , v'=0)

— » Ν Η ( θ ΐ π , v'=0) —• N H (a*A, v"=0)

+

hu

3

λ! = 193 nm λ

2

= 452 nm

λ = 325 nm 3

Figure 5. Processes involved in vacuum UV photofragmentation-laser fluorescence detection of ammonia.

induced


252

MEASUREMENT CHALLENGES IN ATMOSPHERIC CHEMISTRY AMBIENT AIR

Nd.YAG LASER

35Snm + 532nm 532nm •. + 1064nm j—|1064nm \—\ t064nm

TO ELECTRONICS

osc

Figure 6. Instrumental schematic for vacuum UV photofragmentation-laser induced fluorescence measurement of ammonia: SHGC, second harmonic generation crystal; SFMC, sum frequency mixing crystal; BS, beam splitter; BD, beam dump; TP, turning prism; C L , cylindrical lens; R, reflector; TD, trigger diode; OSC, oscillator cell; AMP, amplifier cell; BE, beam expander; G, grating; OC, output coupler; M, mirror; BC, beam combiner; L, lens; A, aperture; PD, photodiode; SC, sample cell; RC, reference cell; FP, filter pack; SAM.PMT, sample cell photomultiplier; REF.PMT, reference cell photomultiplier; PP, additional photomultiplier port; EX, exhaust; and CGI, calibration gas inlet to flow line. (Reproduced with permission from reference 15. Copyright 1990 Optical Society of America.) tensive m a n u a l operation a n d p r o c e d u r e s , still plays an i m p o r t a n t r o l e , a l t h o u g h t y p i c a l l y there is a critical c o m p r o m i s e b e t w e e n adequate d e t e c t i o n l i m i t a n d l o n g exposure t i m e . A n example o f this a p p r o a c h is the filter-pack m e a s u r e m e n t o f n i t r i c a c i d a n d nitrate aerosols. T h e filters i n an automatic s e q u e n c i n g system are exposed for f r o m 1 to 4 h a n d are c h a n g e d once p e r day. T h e filters are taken to the laboratory, extracted, a n d a n a l y z e d b y i o n chromatography. A n i m p o r t a n t aspect o f the m e a s u r e m e n t p r o g r a m is a careful m o n i t o r i n g o f field blanks. T h i s approach is c e r t a i n l y l a b o r - i n t e n s i v e , b u t w i t h careful w o r k l o w detection l i m i t s can b e o b t a i n e d . F o r e x a m p l e , a d e t e c t i o n l i m i t o f 2 p p t r v o f H N 0 w i t h a 2 - h exposure is possible (17). 3

M o r e m o d e r n i n s t r u m e n t a l analysis has b e e n u s e d to i m p r o v e s e n s i t i v i t y a n d response t i m e . S h o w n i n F i g u r e 7 is a schematic d i a g r a m o f an i n s t r u m e n t that has b e e n d e v e l o p e d to measure N O a n d N 0 (18). T h e d e t e c t i o n scheme is based o n the c h e m i l u m i n e s c e n c e p r o d u c e d w h e n N O i n the a m b i e n t air reacts w i t h ~ 1 % ozone a d d e d as a reagent to the s a m p l e d a i r s t r e a m . 2


9.

Γ,

PARRISH & B U H R


Calibration System

253

To Dump I

Teflon Filter

3-Way Valves

Sample Line Xe Arc Lamp Rower Supply

To Dump U

N0 Permeation Tube β 0 ° Ο

~)

Xe Arc Lamp

2

Z3 Shutter Photolysis Tube

Teflon PFA I Tubing l/4"0.D. 1/8" Q Û Mass Flow Controllers

N0 Systemj X

s, δ

δ

en

.ω

Ο

ο

3

NO in N2 Mixture

Ozone System

Ozonizer

cz>

(1 slpm)H Pre-Reaction I Chamber | (30°C) j

Oxygen 3-Way Valve ι Recorder Ratemeter

PMT Power Supply Red Filter PMT, _\j Reaction Vessel (30°C)

Computer

Signal Splitter

Pulse Refrigerated Amp/Disc Housing (-50 C) e

i Pneumatic Valve I Ozone Destruction I Trap Pump (5 Is" )

Photon Counting System

Exhaust

Pumping System

Figure 7. Schematic of 0 chemiluminescence instrument for the measurement of NO and N0 . (Reproduced with permission from reference 18. Copyright 1990 American Geophysical Union.) 3

2


254

MEASUREMENT CHALLENGES INATMOSPHERIC CHEMISTRY

T h e a m b i e n t N O concentration is p r o p o r t i o n a l to t h e m e a s u r e d l i g h t signal. N O alone is m e a s u r e d w h e n t h e a r c - l a m p shutter is closed, a n d N 0 c a n b e d e t e r m i n e d from the increase i n the signal w h e n t h e shutter is o p e n e d . T h i s i n s t r u m e n t has a detection l i m i t o f 2 a n d 10 p p t r v for N O a n d N 0 , r e spectively, for a 10-s averaging t i m e . W i t h these nonspectroscopic approaches there is no guarantee o f spec2

2

ificity, a n d e v e n for t h e spectroscopic t e c h n i q u e s , p r o b l e m s m a y exist. A n essential c o m p o n e n t of t e c h n i q u e d e v e l o p m e n t is t h e evaluation of p o t e n t i a l s a m p l i n g artifacts a n d interferences. T h i s evaluation w e l l m a y r e q u i r e m o r e t i m e a n d effort than the i n s t r u m e n t d e v e l o p m e n t itself.

Measurement Pfaforms In Situ Measurements: Surface Sites. F o r t h e d e t e r m i n a t i o n of t e m p o r a l cycles a n d t r e n d s , surface sites w h e r e l o n g - t e r m m e a s u r e m e n t s can b e c a r r i e d out are i d e a l . D e p e n d i n g o n the meteorological c o n d i t i o n s , m a n y air masses w i t h different characteristics a n d histories w i l l g e n e r a l l y b e transported to t h e site. A u t o m a t i c i n s t r u m e n t operation is advantageous so that t h e data c a n b e c o l l e c t e d c o n t i n u a l l y over w e e k s , m o n t h s , o r l o n g e r w i t h o u t constant operator c o n t r o l . I n this a p p l i c a t i o n the r e q u i r e m e n t s for i n s t r u m e n t response t i m e are usually easily m e t ; a 1 - m i n o r l o n g e r t i m e average is generally adequate for surface m e a s u r e m e n t s unless flux d e t e r minations are d e s i r e d (see discussion i n t h e f o l l o w i n g sections). C o n c e n t r a t i o n s at surface sites are often affected b y t h e p r o x i m i t y o f the surface. T h e surface m a y e m i t the species, as is t h e case for N O , o r t h e species m a y b e d e p o s i t e d at t h e surface, as is t h e case for H N 0 . I n e i t h e r case, t h e a t m o s p h e r i c concentration m e a s u r e d w i t h i n several meters o f t h e surface m a y b e significantly p e r t u r b e d f r o m t h e average for t h e t r o p o s p h e r e as a w h o l e o r e v e n for the b o u n d a r y layer (the lowest layer of the t r o p o s p h e r e i n d i r e c t t h e r m a l contact w i t h t h e surface; its thickness varies f r o m 1 0 m or less at n i g h t to 1 0 m o r m o r e d u r i n g the day, at least over land). T h e r e f o r e , the surface complicates t h e i n t e r p r e t a t i o n o f c o n c e n t r a t i o n m e a s u r e m e n t s . H o w e v e r , p r o p e r measurements near t h e surface c a n b e u s e d to d e t e r m i n e surface fluxes o f the species. 3

2

3

In Situ Measurements: Aircraft.

I n situ measurements can also b e

made from aircraft platforms, b u t the e n g i n e e r i n g r e q u i r e m e n t s are m u c h m o r e stringent. T h e s e challenges i n c l u d e design of compact, l o w - w e i g h t , l o w - p o w e r - c o n s u m p t i o n i n s t r u m e n t s ; a c h i e v e m e n t o f q u i c k start-up times a n d automatic operation to t h e fullest extent possible; a n d , because t h e aircraft is m o v i n g r a p i d l y t h r o u g h the air, a fast response t i m e (approximately 1 H z o r greater) to get good spatial i n f o r m a t i o n . A n e x a m p l e is t h e N O N O i n s t r u m e n t that has b e e n flown o n t h e E R - 2 aircraft that t h e N a t i o n a l (y


9.

PARRISH & B U H R


255

A e r o n a u t i c s a n d Space A d m i n i s t r a t i o n ( N A S A ) operates. T h i s aircraft is a c o n v e r t e d U - 2 spy plane that was u s e d i n , a m o n g other studies, the A n t a r c t i c m i s s i o n to investigate the ozone hole (19). T h i s i n s t r u m e n t w e i g h s 170 k g , consumes about 1 k W , a n d has a 1 - H z response. A t takeoff the p i l o t actuates one s w i t c h , w h i c h causes the i n s t r u m e n t to automatically b e g i n o p e r a t i o n and collect a n d store the measurements for later r e t r i e v a l . T h e d e p l o y m e n t of such i n s t r u m e n t a t i o n o n t r o p o s p h e r i c aircraft is perhaps m o r e r e l a x e d , at least i n size, p o w e r , a n d w e i g h t constraints. F o r e x a m p l e , the N A S A L o c k h e e d E l e c t r a aircraft was e q u i p p e d w i t h a w i d e v a r i e t y of i n s t r u m e n t a t i o n for the m e a s u r e m e n t of N O , N 0 , P A N , H N 0 , a n d N O (as w e l l as o t h e r trace species) d u r i n g the G l o b a l T r o p o s p h e r e E x p e r i m e n t / C h e m i c a l I n s t r u m e n t a t i o n Test a n d E v a l u a t i o n ( G T E / C I T E - 2 ) study (20). 2

3

? /

A n aircraft has three obvious advantages o v e r a surface site. F i r s t , the aircraft can measure v e r t i c a l a n d h o r i z o n t a l profiles of concentrations; s u c h measurements are not possible at the surface. H o w e v e r , because the t y p i c a l aircraft travels h o r i z o n t a l l y m u c h faster than it ascends or descends, it m a y be difficult to d e c o n v o l u t e v e r t i c a l from h o r i z o n t a l variations. S e c o n d , the aircraft allows the investigator to choose the g e n e r a l t y p e o f air parcels to study r a t h e r t h a n s i m p l y a l l o w i n g s a m p l i n g of w h a t e v e r parcels are b r o u g h t to a site (as on the surface). T h i r d , the aircraft can measure concentrations free f r o m the surface influences discussed i n the p r e c e d i n g sections. W i t h an aircraft platform the data set that is c o l l e c t e d is l i k e l y m o r e l i m i t e d i n t i m e t h a n is possible o n the surface. H o w e v e r , this l i m i t a t i o n is at least partially c o m p e n s a t e d b y the aircraft's a b i l i t y to r a p i d l y s a m p l e m a n y different air parcels, whereas at a surface site different parcels m u s t b e transported to it. H o w e v e r , d i u r n a l a n d seasonal cycles may b e m o r e difficult to measure f r o m an aircraft t h a n f r o m the surface. In Situ Measurements: Balloons. Balloons c u r r e n t l y p r o v i d e the o n l y i n situ platform that allows access to the u p p e r part of the stratosphere (above 20 km). T h e e n g i n e e r i n g r e q u i r e m e n t s are s i m i l a r to those for aircraft except for a m o r e relaxed t i m e response. R e g i o n a l coverage f r o m balloons is difficult, p a r t i c u l a r l y because the l a u n c h i n g facilities for the large stratos p h e r i c balloons are v e r y l i m i t e d a n d generally l o c a l i z e d i n the m i d l a t i t u d e s . H o w e v e r , v e r t i c a l profiles w i t h o u t h o r i z o n t a l d i s t o r t i o n are the natural data c o l l e c t i o n m o d e . M e a s u r e m e n t c o n t a m i n a t i o n d u e to emissions f r o m the b a l l o o n is a p o t e n t i a l p r o b l e m . A b a l l o o n - b o r n e , o p e n p a t h , tunable d i o d e laser s p e c t r o m e t e r (21) p r o vides a p a r t i c u l a r l y elegant t e c h n i q u e that c o m b i n e s the advantages o f i n situ a n d r e m o t e s a m p l i n g . T h e radiation a b s o r p t i o n p a t h is d e f i n e d b y the laser o n the b a l l o o n gondola a n d a retro reflector s u s p e n d e d u p to 500 m b e l o w . T h u s , a w e l l - d e f i n e d p a r c e l of air is a n a l y z e d a n d the effects o f s a m p l i n g inlets are a v o i d e d . N O , N 0 , H N 0 , N 0 , a n d 0 have b e e n m e a s u r e d s i m u l t a n e o u s l y (22). 2

3

2

3


256

M E A S U R E M E N T C H A L L E N G E S IN ATMOSPHERIC CHEMISTRY

Remote Measurements. L o n g - p a t h differential a b s o r p t i o n m e a surements of several n i t r o g e n species have b e e n m a d e f r o m the surface, from aircraft, from balloons, a n d from satellites. T h e s e m e a s u r e m e n t s are all c h a r a c t e r i z e d b y light that passes f r o m a source t h r o u g h some a t m o s p h e r i c p a t h to a detector. Surface-based m e a s u r e m e n t s have u s e d b o t h artificial light sources w i t h i n the troposphere a n d the natural sources of the s u n a n d the m o o n , e i t h e r d i r e c t rays or sky-scattered r a d i a t i o n . T h e artificial l i g h t sources can shine d i r e c t l y to the detector f r o m a distance o r can b e reflected to the detector from a m i r r o r some distance away so that the detector a n d light source can be colocated. O n e e x a m p l e o f such an approach has b e e n effected i n C o l o r a d o , w h e r e a v i s i b l e - U V l i g h t source (a x e n o n arc lamp) is focused into a b e a m a n d passed 10.3 k m across a v a l l e y to a retro-reflector array. T h u s , the absorption m e a s u r e m e n t is c a r r i e d out o v e r n e a r l y a 2 1 k m path length. A t m o s p h e r i c c o l u m n absorption m e a s u r e m e n t s f r o m the surface are possible for N O , N 0 , N O , H N 0 , a n d C l O N O o (23-25). T h e s e m e a s u r e m e n t s have d e f i n e d the seasonal cycle (25) as w e l l as m u c h m o r e r a p i d variations (26) i n the stratospheric levels of N 0 . U n d e r favorable c o n d i t i o n s these m e a s u r e m e n t s can y i e l d i n f o r m a t i o n c o n c e r n i n g the v e r t i c a l profiles o f the m e a s u r e d species (24, 26). S u c h techniques can also b e u s e d f r o m aircraft platforms (27, 28). L o n g - p a t h absorption measurements f r o m satellites are also possible. F o r e x a m p l e , F i g u r e 8 shows some results from the A t m o s p h e r i c Trace M o l e c u l e Spectroscopy ( A T M O S ) e x p e r i m e n t (29) that was c a r r i e d out o n Spacelab 3. T h e l i g h t source is solar i n f r a r e d radiation, w h i c h passes t h r o u g h progressively d e e p e r layers of the a t m o s p h e r e as the satellite m o v e s i n t o a n d out of the earth's shadow. T h e investigators c o u l d extract the average v e r t i c a l profiles i n the stratosphere of the several n i t r o g e n species i n c l u d e d i n F i g u r e 8 plus N 0 (30) a n d N 0 (31). M e a s u r e m e n t s o f o x i d i z e d n i t r o g e n species i n the stratosphere have also b e e n m a d e f r o m the Stratospheric A e r o s o l a n d Gas E x p e r i m e n t ( S A G E ) , L i m b Infrared M o n i t o r of the Stratosphere ( L I M S ) , a n d Solar Mésosphère E x p l o r e r ( S M E ) satellite e x p e r i m e n t s ; reference 32 gives a r e v i e w w i t h references to the satellite m e t h o d s . Infrared e m i s s i o n spectra have b e e n u s e d to extract the concentrations of H N 0 (33), N 0 (34, 35), a n d N 0 (36) from b a l l o o n - b o r n e , c r y o g e n i c a l l y c o o l e d interferometers. 2

i 3

3

3

2

3

2

5

2

5

2

General Challenges T h e challenges that are p r e s e n t l y faced i n the field can be d i v i d e d i n t o five general categories: 1. E n g i n e e r i n g challenges specific to the p a r t i c u l a r m e a s u r e m e n t approach, p l a t f o r m , a n d a p p l i c a t i o n . T h e y have b e e n i n t r o -


9.

PARRISH & B U H R


257

Odd Nitrogen Volume Mixing Rotio

Figure 8. Measurements of odd nitrogen compounds in the stratosphere by the ATMOS experiment on Spacelab 3. (Reproduced with permission from reference 29. Copyright 1988 American Geophysical Union.)

d u c e d i n the p r e c e d i n g sections, a n d , a l t h o u g h t h e y are o f course v e r y i m p o r t a n t , they are p r o b a b l y different for each e x p e r i m e n t a n d thus, w i t h the exception o f r e q u i r e d response t i m e s , are not discussed further. 2. D e m o n s t r a t i o n that t e c h n i q u e s n o w i n use are specific, s e n sitive, accurate, a n d precise e n o u g h for the m e a s u r e m e n t s envisioned. 3. E x t e n s i o n of m e a s u r e m e n t capabilities. T e c h n i q u e s m u s t be d e v e l o p e d for species that at present cannot b e m e a s u r e d . A d d i t i o n a l l y , for species p r e s e n t l y m e a s u r e d , n e w t e c h n i q u e s , as w e l l as adaptations of p r e s e n t t e c h n i q u e s to o t h e r m e a s u r e m e n t platforms, are r e q u i r e d . 4. T h e simultaneous m e a s u r e m e n t of as m a n y species as possible. As was s h o w n i n the p h o t o c h e m i c a l r e l a t i o n s h i p examples, and as is s h o w n i n a few examples b e l o w , s u c h simultaneous


258


measurements y i e l d m u c h a d d i t i o n a l insight into a t m o s p h e r i c chemistry. 5. T h e p l a n n i n g a n d c o m p l e t i o n of w e l l - d e s i g n e d field studies that w i l l y i e l d a m a x i m u m of i n f o r m a t i o n . T h e s e general challenges are addressed b y examples of specific challenges that exemplify t h e m .

Specific Challenges Rigorous Field Intercomparisons.

T o quantitate measurement u n -

certainties, the atmospheric c h e m i s t r y c o m m u n i t y has d e v e l o p e d a p r o c e d u r e for c a r r y i n g out rigorous field intercomparisons. T h e features of the most i n s t r u c t i v e of the intercomparisons that have b e e n c o m p l e t e d i n c l u d e • i n v o l v e m e n t of several different techniques together at the same site m e a s u r i n g the same species u n d e r t y p i c a l o p e r a t i n g conditions, • s u p e r v i s i o n of the i n t e r c o m p a r i s o n b y an i n d e p e n d e n t referee, • analysis of each i n v e s t i g a t o r s results i n a b l i n d m a n n e r f r o m the other investigators to a p u b l i c a t i o n - r e a d y status, • not o n l y simultaneous a m b i e n t m e a s u r e m e n t s , b u t also s a m p l i n g of p r e p a r e d mixtures of standards as w e l l as p o t e n t i a l interferences i n air i n o r d e r to facilitate the i n t e r p r e t a t i o n of the results that are collected, a n d • p u b l i c a t i o n of the results i n a refereed j o u r n a l . A s an example, a recent i n t e r c o m p a r i s o n (37) i n c l u d e d t h r e e N 0 m e a s u r e m e n t techniques: a T D L A S - b a s e d system a n d two c h e m i c a l - b a s e d s y s t e m s — the p h o t o l y s i s - o z o n e c h e m i l u m i n e s c e n c e system d i a g r a m e d i n F i g u r e 7 a n d an i n s t r u m e n t based o n N 0 p l u s l u m i n o l c h e m i l u m i n e s c e n c e . A b o v e 2 p p b v the three i n s t r u m e n t s gave s i m i l a r results, b u t at s u b - p p b v the results from the three techniques b e c a m e d i s s i m i l a r . Tests o n the p r e p a r e d m i x t u r e s s h o w e d that the l u m i n o l results w e r e affected b y expected interferences from 0 a n d P A N . N o interferences w e r e f o u n d i n the T D L A S system, b u t near the detection l i m i t the data analysis procedures calculated levels of N 0 that w e r e too h i g h . T h e o u t c o m e of this i n t e r c o m p a r i s o n was close to the i d e a l : the sensitivity, specificity, accuracy, a n d p r e c i s i o n o f each i n s t r u m e n t w e r e objectively a n a l y z e d ; previous data sets t a k e n b y different systems can n o w be r e l i a b l y evaluated; a n d each investigator was able to p e r c e i v e areas i n w h i c h the t e c h n i q u e c o u l d b e i m p r o v e d . 2

2

3

2

C o m p l e t e d intercomparisons that have r e a c h e d d e f i n i t i v e conclusions have i n v o l v e d N O (reference 38 a n d references c i t e d therein), NO (39), a n d N H (40) i n a d d i t i o n to others for N 0 (reference 41 a n d references c i t e d y

3

2


9.

PARRISH & B U H R


259

therein). F o r these species the a t m o s p h e r i c c h e m i s t r y c o m m u n i t y can o b j e c t i v e l y evaluate the c u r r e n t measurements of these species, at least i n the troposphere. T h e intercomparisons have d e m o n s t r a t e d that m e a s u r e m e n t s of N 0 i n v o l v i n g surface c o n v e r s i o n of N O to N O have significant i n t e r f e r ences that are d u e to the conversion o f n i t r o g e n species o t h e r t h a n N 0 . 2

£

2

M e a s u r e m e n t techniques for two other n i t r o g e n species have b e e n i n t e r c o m p a r e d , w i t h i n s t r u c t i v e b u t less d e f i n i t i v e results. T w o n e a r l y i d e n t i c a l systems for P A N measurements w e r e i n t e r c o m p a r e d as part of the N A S A C I T E 2 p r o g r a m (42). G e n e r a l l y , the agreement b e t w e e n the i n s t r u m e n t s for measurements i n the remote troposphere was w i t h i n the e x p e c t e d l i m i t s of accuracy a n d p r e c i s i o n . H o w e v e r , the results i n d i c a t e d that t h e r e w e r e difficulties i n the calibration of this species a n d that at least for some p e r i o d s there w e r e significant disagreements b e t w e e n the results of the t w o systems. A n a d d i t i o n a l i n t e r c o m p a r i s o n o f methods to measure P A N w o u l d b e d e s i r able, i n c l u d i n g at least one f u n d a m e n t a l l y different t e c h n i q u e i f it can b e d e v e l o p e d . A d d i t i o n a l l y , an i n t e r c o m p a r i s o n of e x i s t i n g methods u s e d to calibrate P A N i n s t r u m e n t s w o u l d b e w o r t h w h i l e , as w o u l d d e v e l o p m e n t o f n e w calibration m e t h o d s , g i v e n the d e m o n s t r a t e d uncertainties i n this c r i t i c a l procedure. S e v e r a l f o r m a l a n d i n f o r m a l intercomparisons of n i t r i c a c i d m e a s u r e m e n t techniques have b e e n c a r r i e d out (43-46); these i n t e r c o m p a r i s o n s i n v o l v e a m u l t i t u d e of t e c h n i q u e s . T h e i n situ m e a s u r e m e n t o f this species has p r o v e n difficult because it v e r y r a p i d l y absorbs o n any i n l e t surfaces a n d because it is i n v o l v e d i n r e v e r s i b l e s o l i d - v a p o r e q u i l i b r i a w i t h aerosol nitrate species. T h e s e e q u i l i b r i a can be d i s t u r b e d b y the s a m p l i n g process; these d i s t u r bances l e a d to negative or positive errors i n the d e t e r m i n a t i o n o f the a m b i e n t vapor-phase concentration. T h e intercomparisons f o u n d differences of the o r d e r of a factor of 2 generally, a n d u p to at least a factor of 5 at levels b e l o w 0.2 p p b v . T h e s e studies clearly indicate that the i n t e r c o m p a r e d t e c h n i q u e s do not a l l o w the u n e q u i v o c a l d e t e r m i n a t i o n o f n i t r i c a c i d i n the a t m o s p h e r e . A laser-photolysis, fragment-fluorescence m e t h o d (47) a n d an active c h e m i c a l i o n i z a t i o n , mass s p e c t r o m e t r i c t e c h n i q u e (48) w e r e r e c e n t l y r e p o r t e d for this species. T h e s e approaches m a y p r o v i d e m o r e definite specificity for H N 0 . C h a l l e n g e s c l e a r l y r e m a i n i n the m e a s u r e m e n t o f this species. 3

Development of Techniques for Currently Unmeasured Species in the Troposphere. T h e r e is e v i d e n c e that t h e r e are a d d i t i o n a l m e m b e r s of the n i t r o g e n f a m i l y that have not b e e n m e a s u r e d . W i t h the possible exceptions of H N 0 a n d particulate N 0 ~ , reasonably r e l i a b l e t e c h n i q u e s are c u r r e n t l y available for i n situ m e a s u r e m e n t o f the concentrations of the major c o n t r i b u t o r s to the N O f a m i l y i n the r u r a l t r o p o s p h e r e . I n a d d i t i o n , a m e a s u r e m e n t o f the total f a m i l y c o n c e n t r a t i o n is available. T h e r e f o r e the total of the concentrations of the i n d i v i d u a l l y m e a s u r e d species can be c o m p a r e d w i t h the m e a s u r e d f a m i l y c o n c e n t r a t i o n . T h i s c o m p a r i s o n can t h e n 3

3

y


260


p r o v i d e a check for the c o n t r i b u t i o n o f any u n m e a s u r e d species. I n this c o m p a r i s o n the p r o b l e m s i n the m e a s u r e m e n t of H N 0 a n d particulate N 0 ~ c o n t r i b u t e r e l a t i v e l y small uncertainties because t h e i r s u m enters the c a l c u l a t i o n ; because the s u m is u s e d , the effect o f the e q u i l i b r i a shifts is e l i m inated. 3

3

A s an example of an evaluation of the N O b u d g e t , F i g u r e 9 shows the m e a s u r e m e n t results f r o m three f i e l d studies. T h e ratio of the s u m of the five i n d e p e n d e n t l y m e a s u r e d species to the m e a s u r e d NO l e v e l as a f u n c t i o n of N O l e v e l is s h o w n . I n each of these studies, for levels of N O . b e l o w about 2 p p b v the m e a s u r e d species d i d not account for the total m e a s u r e d NO I m p o r t a n t c o n t r i b u t i o n s to N O , a p p r o a c h i n g 30 to 4 0 % u n d e r r e l a t i v e l y clean conditions, m u s t c o m e f r o m c u r r e n t l y u n m e a s u r e d species at these two sites. T h e closed circles show the results of calculations from a m o d e l e x c l u d i n g organic nitrates other t h a n P A N ( M . T r a i n e r , p e r s o n a l c o m m u n i c a t i o n ) . T h e difference b e t w e e n the c a l c u l a t e d NO c o n c e n t r a t i o n a n d the calculated s u m o f the concentrations o f the five i n d i v i d u a l species was c o m p o s e d of a v a r i e t y of organic nitrates. P r e d i c t e d species i n c l u d e a c y l nitrates i n a d d i t i o n to P A N , a l k y l nitrates ( R O N 0 ) , a n d d i f u n c t i o n a l organic nitrates of the f o r m R ' O N 0 , w h e r e R ' i n c l u d e d e i t h e r a c a r b o n y l o r h y d r o x y l moiety. y

y

v

A

r

y

y

2

2

>• Ο 1.2

1

Co

Ο

I I I 11

τ τ

ττ

1.0

2

+

Ίο

.8

Ο Ζ χ •

Model

A Scotia Range 1988 Ο Scotia Rangeai986 ο

.2

+ c——«

Ο

•

Niwot Ridge 1987

I I I I III

Mill

I

I

I

M i l l

0.1

10

[NO ] (ppbv) x

Figure 9. Results from three field studies for the ratio of the sum ofNO species concentration to total NO concentration as a function of NO concentration. The model result at the higher NO levels is for the conditions at Scotia Range, Pennsylvania, and that for the lower NO levels is for the conditions at Niwot Ridge, Colorado (M. Trainer, personal communication). y

y

x

x

K


9.

PARRISH & B U H R

261


A n u m b e r o f o t h e r theoretical a n d laboratory studies have p r e d i c t e d t h e existence o f a l k y l a n d m u l t i f u n c t i o n a l organic nitrates i n t h e a t m o s p h e r e (9, 49-56). T h e a t m o s p h e r i c c h e m i s t r y o f the organic nitrates was r e c e n t l y r e v i e w e d (57). S o m e progress has b e e n made i n m e a s u r i n g these o t h e r organic nitrates, i n c l u d i n g p e r o x y p r o p i o n y l nitrate ( P P N ) , t h e t h r e e - c a r b o n analog o f P A N , p e r o x y b e n z o y l nitrate ( P B z N ) , a n d t h e Q - Q a l k y l nitrates ( R O N 0 ) . P P N has b e e n d e t e c t e d i n t h e same c h r o m a t o g r a p h i c m e a s u r e m e n t s that w e r e u s e d to measure P A N b y a n u m b e r o f investigators (58-60). P e r o x y b e n z o y l nitrate has b e e n m e a s u r e d b y first c o l l e c t i n g a sample i n a b u b b l e r c o n t a i n i n g m e t h a n o l - N a O H a n d t h e n u s i n g solvent extraction o n t h e r e s u l t i n g m e t h y l benzoate, w h i c h was q u a n t i f i e d w i t h gas c h r o m a t o g r a p h y - f l a m e i o n i z a t i o n d e t e c t i o n ( G C - F I D ) (57, 61). T h e a l k y l nitrates have b e e n m e a s u r e d b y a n u m b e r o f laboratories b y u s i n g e i t h e r p a c k e d o r c a p i l l a r y c o l u m n gas c h r o matography c o u p l e d w i t h e i t h e r an e l e c t r o n capture detector ( E C D ) ( 6 2 63) o r w i t h a nitrogen-specific N O detector (64). T h e m e a s u r e m e n t s that have b e e n made o f P P N a n d t h e a l k y l nitrates, i n c o n j u n c t i o n w i t h N O m e a s u r e m e n t s , have shown that the P P N a n d R O N 0 c o n t r i b u t i o n s to N O are not great e n o u g h to balance t h e N O , , budget. T h e r e f o r e , attempts m u s t be m a d e to measure t h e other organic nitrate species p r e d i c t e d b y m o d e l calculations. 2

? /

? /

2

{ /

M e a s u r e m e n t s of these r e l a t i v e l y m i n o r species w i l l n o t o n l y c o m p l e t e the b u d g e t o f N O b u t w i l l also indicate i f o u r u n d e r s t a n d i n g o f the h y d r o carbon oxidation schemes i n t h e atmosphere is c o m p l e t e . T h e organic n i trates that c o m p l e t e d t h e N O b u d g e t i n t h e e x a m p l e i n F i g u r e 9 arose p r i m a r i l y from t h e oxidation o f the naturally e m i t t e d h y d r o c a r b o n , isoprene (2-methylbutadiene). T o demonstrate t h e oxidation m e c h a n i s m s b e l i e v e d to be i n v o l v e d i n t h e p r o d u c t i o n o f m u l t i f u n c t i o n a l organic nitrates, a partial O H oxidation sequence for isoprene is discussed. T h e reaction pathways d e s c r i b e d are m o d e l e d closely to those d e s c r i b e d i n reference 52 for p r o p e n e . T h e first step i n this oxidation is a d d i t i o n o f the h y d r o x y l radical across a d o u b l e b o n d . S u b s e q u e n t a d d i t i o n o f 0 results i n the f o r m a t i o n o f a p e r o x y radical. W i t h t h e t w o d o u b l e bonds present i n isoprene, t h e r e are four possible isomers, as s h o w n i n reactions 2 - 5 : ? /

? /

2

+ OH

C H C ( C H ) C H C H[ 2

3

2

o

2

» o

2

>

o

2

2

2

3

(0.15) OOCH C(CH )(OH)CHCH 2

(2)

2

3

2

(3)

(0.35) CH C(CH )CH(00)CH OH

(4)

» (0.15) CH C(CH )CH(OH)CH 00

(5)

» o

(0.35) HOCH C(CH )(00)CHCH

2

2

3

3

2

2


262


T h e b r a n c h i n g ratios s h o w n are estimates based o n reference 65. T h e f u r t h e r oxidation o f each o f the isomers is s i m i l a r , so o n l y the first i s o m e r w i l l b e e x a m i n e d i n d e t a i l . I n c o n t i n e n t a l areas w i t h at least tens o f p p t r v ' s o f N O , the p e r o x y radical p r o d u c e d i n the first step w i l l react w i t h N O . T h i s reaction can result i n e i t h e r oxidation of N O to N O or p r o d u c t i o n o f a n organic nitrate (bold type indicates organic nitrates that are a s s u m e d to b e stable): z

HOCH C(CH )(00)CHCH 2

3

2

> (0.7) N 0

+

NO + HOCH C(CH )(0)CHCH

2

2

3

> (0.3) HOCH C(CH )(ON0 )CHCH 3

2

2

(6)

2

(7)

2

T h e b r a n c h i n g ratio s h o w n h e r e for the p r o d u c t i o n o f t h e organic n i t r a t e is based o n reference 65. B o t h o f the organic products s t i l l c o n t a i n one d o u b l e b o n d , so f u r t h e r oxidation is l i k e l y . T h e alkoxy radical p r o d u c e d i n the first step r a p i d l y decomposes; m e t h y l v i n y l k e t o n e a n d f o r m a l d e h y d e are p r o d u c e d , as w e l l as a h y d r o p e r o x y radical: HOCH C(CH )(0)CHCH 2

3

°

2 ,

2

> CH CHC(0)CH

f a S t

2

3

+ HCHO + H0

(8)

2

T h e organic nitrate p r o d u c e d i n reaction 7 may u n d e r g o f u r t h e r o x i d a t i o n b y the h y d r o x y l radical v i a a d d i t i o n across the r e m a i n i n g d o u b l e b o n d as s h o w n i n reactions 9 a n d 10. A g a i n , i n air the r e s u l t i n g radicals r a p i d l y a d d 0 to form peroxy radicals: 2

HOCH C(CH )(ON0 )CHCH + O H 2

3

2

2

(0.65) H O C H C ( C H ) ( O N 0 ) C H ( 0 0 ) C H O H

(9)

(0.35) H O C H C ( C H ) ( O N 0 ) C H ( O H ) C H 0 0

(10)

2

-2*»

3

2

2

3

2

2

2

I n a m a n n e r s i m i l a r to the reaction pathway s h o w n i n reactions 6 a n d 7, the peroxy radicals generated i n reactions 9 a n d 10 w i l l react w i t h N O to y i e l d e i t h e r N O a n d an alkoxy radical or a d i n i t r a t e : z

HOCH C(CH )(ON0 )CH(00)CH OH + 2

3

2

2

NO

» HOCH C(CH )(ON0 )CH(0)CH OH + N 0 2

3

2

2

2

> HOCH C(CH )(ON0 )CH(ON0 )CH OH 2

3

2

2

2

(11)

(12)

T h e stability of the dinitrate p r o d u c e d i n reaction 12 is not k n o w n . T h e alkoxy radical p r o d u c e d i n reaction 11 p r o b a b l y decomposes a n d t h e n forms


9.

PARRISH & B U H R

263


the organic nitrate s h o w n i n reaction 13, f o r m a l d e h y d e , a n d a h y d r o p e r o x y radical. A l t e r n a t i v e l y , the d e c o m p o s i t i o n of this alkoxy radical can result i n h y d r o x y acetaldehyde a n d an organic nitrate p e r o x y radical as s h o w n i n reaction 14. HOCH C(CH )(ON0 )CH(0)CH OH 2

3

2

2

HOCH C(CH )(ON0 )CHO + H C H O + H 0 2

3

2

2

HOCH C(CH )(ON0 )00 + OHCH CHO 2

3

2

2

(13) (14)

T h e fate o f the organic nitrate peroxy radical p r o d u c e d i n reaction 14 is p r o b a b l y oxidation of N O to N 0 a n d t h e n d e c o m p o s i t i o n , y i e l d i n g a c e t y l nitrate, f o r m a l d e h y d e , a n d a h y d r o p e r o x y radical as s h o w n i n reactions 15 and 16. 2

HOCH C(CH )(ON0 )00 + 2

3

2

NO

> HOCH C(CH )(ON0 )0+ N 0 2

3

2

(15)

2

HOCH C(CH )(ON0 )0 2

3

2

HCHO + H0

2

+ CH C(0)ON0 3

2

(16)

T h e f u r t h e r d e c o m p o s i t i o n of acetyl nitrate i n the atmosphere has not b e e n s t u d i e d . T h e oxidation of isoprene b y the h y d r o x y l radical p r o c e e d s v i a r e p e a t e d steps of O H a d d i t i o n across the d o u b l e b o n d , f o l l o w e d b y a d d i t i o n of 0 to f o r m a peroxy radical. T h e peroxy radical t h e n e i t h e r oxidizes N O to N 0 or adds N O to f o r m an organic nitrate. T h e alkoxy radical p r o d u c e d i n the f o r m e r step u n d e r w e n t d e c o m p o s i t i o n to f o r m b o t h stable a n d reactive products. A n u m b e r of possible pathways exist for f o r m i n g p r e s u m a b l y stable organic nitrates (bold i n reactions 7 t h r o u g h 16). 2

2

In a d d i t i o n to b e i n g o x i d i z e d b y the h y d r o x y l radical, alkenes m a y react w i t h the N 0 radical as has b e e n d e s c r i b e d b y several investigators (52, 56, 66). L i s t e d i n T a b l e I are some of the organic nitrates that have b e e n p r e d i c t e d to b e p r o d u c e d v i a reaction of O H a n d N 0 w i t h i s o p r e n e a n d p r o pene. Analogous c o m p o u n d s w o u l d b e expected f r o m o t h e r s i m p l e alkenes and from terpenes s u c h as a - a n d β-pinene. O t h e r possible organic nitrates may b e p r o d u c e d v i a the oxidation o f aromatic c o m p o u n d s (53, 54) a n d the oxidation of carbonaceous aerosols (67). Q u a n t i t a t i v e d e t e r m i n a t i o n o f these species has not b e e n m a d e i n the a m b i e n t atmosphere. 3

3

T h e p o l a r nature o f m a n y o f these species m a y dictate the use of e i t h e r solvent extraction f o l l o w e d b y gas or l i q u i d c h r o m a t o g r a p h y o r s u p e r c r i t i c a l e x t r a c t i o n - c h r o m a t o g r a p h y ( S F E - S F C ) i n o r d e r to m a k e effective a m b i e n t measurements. W h e n the measurements of these organic species are a v a i l -


264


Table I. Possible Unmeasured Atmospheric Organic Nitrates Parent

Organic Nitrate Formula HOCH C(CH )(ON0 )CHCH

Hydrocarbon

CH C(CH )CHCH

2

HOCH C(CH )(ON0 )CH(ON0 )CH OH

CH C(CH )CHCH

2

HOCH C(CH )(ON0 )CHO

CH C(CH )CHCH

2

CH C(0)ON0

CH C(CH )CHCH

2

2

2

2

3

2

3

2

2

3

3

2

2

2

3

2

2

3

2

2

3

2

CH CH(0)CH ON0

3

C H 3

6

CH CH(ON0 )CH ON0 "

C H 3

6

CH CH(OH)CH ON0

C H

6

3

3

2

2

3

2

E

2

2

2

2

&

CH CH(ONQ )CH OH 3

2

3

B

2

"Reference 52; organic nitrate produced via addition of an N 0 radical. ''Reference 52; organic nitrate produced via O H oxidation of propene. 3

able it s h o u l d be possible to d e t e r m i n e i f any other species m a k e significant c o n t r i b u t i o n s to N O . y

Completion of Field Studies in the Troposphere with Better Spatial Coverage, A l l of the examples of tropospheric measurements i n this chapter w e r e made at surface sites w i t h the i n s t r u m e n t inlets w i t h i n 4 to 10 m of the g r o u n d . W i t h the i m p o r t a n t influences of the surface o n the near-surface concentrations of some atmospheric species a n d the lack of spatial i n f o r m a t i o n from surface studies, it is i m p o r t a n t to coordinate the surface measurements w i t h aircraft (or balloon) m e a s u r e m e n t s . S o m e aircraft measurements of n i t r o g e n species i n the troposphere have b e e n m a d e , b u t it is i m p o r t a n t to ensure that the m e a s u r e m e n t t e c h n i q u e s o n the surface a n d i n the air give e q u i v a l e n t results. T h i s assurance can o n l y b e a c c o m p l i s h e d t h r o u g h careful i n t e r c o m p a r i s o n of i n s t r u m e n t s u t i l i z e d i n each p l a t form. F i g u r e 10 shows an example of n e e d e d data that cannot b e o b t a i n e d from surface studies; the m o d e l p r e d i c t e d n i t r i c a c i d concentrations are s h o w n as a function of altitude i n the troposphere u p to 2000 m i m m e d i a t e l y before sunrise. T h r e e scenarios are g i v e n : no n i g h t t i m e n i t r i c a c i d source; i n c l u s i o n of n i t r i c acid f r o m nitrate radicals reacting w i t h c a r b o n y l c o m p o u n d s a n d h y d r o p e r o x y radicals; a n d the a d d i t i o n of N O r e a c t i n g o n aerosols to p r o d u c e n i t r i c a c i d . A t the surface, d e p o s i t i o n f r o m the shallow, near-surface layer u n d e r a l o w - l y i n g n o c t u r n a l i n v e r s i o n reduces the n i t r i c acid concentration to near zero at night. M e a s u r e m e n t s a n d calculations for all three scenarios agree o n this characteristic, so surface m e a s u r e m e n t s cannot give any i n f o r m a t i o n c o n c e r n i n g these postulated n i g h t t i m e reactions. H o w e v e r , i f it w e r e possible to measure a v e r t i c a l profile of n i t r i c a c i d , the v a l i d i t y of each scenario c o u l d be assessed. M e a s u r i n g v e r t i c a l profiles of the nitrate radicals a n d N 0 w o u l d be e v e n m o r e i n f o r m a t i v e , b u t this m e a s u r e m e n t w o u l d r e q u i r e the d e v e l o p m e n t of n e w t e c h n i q u e s as discussed i n the next section. 2

2

s

5

O n c e d e v e l o p e d , pilotless aircraft w i t h l o n g f l i g h t - t i m e capabilities w i l l b e an e x c i t i n g n e w platform for e x t e n d i n g spatial coverage of m e a s u r e m e n t s ,


9.

PARRISH & B U H R

0

265


5

10 HNO3

15

20

(ppbv)

Figure 10. Nighttime vertical distributions of nitric acid predicted by model calculations for three scenarios. (Adapted with permission from reference 8. Copyright 1991 American Geophysical Union.)

b o t h i n the u p p e r troposphere a n d the l o w e r stratosphere. F o r e x a m p l e , the B o e i n g C o n d o r (68) can operate at u p to 20 k m , can r e m a i n aloft for several days, a n d can carry a p a y l o a d of 800 k g . U t i l i z a t i o n o f s u c h an aircraft w o u l d a l l o w measurements b y a sophisticated suite o f i n s t r u m e n t a t i o n at any p o i n t from the m i d d l e troposphere to the l o w e r stratosphere.

Development of In Situ Techniques for Additional Inorganic NO

y

Species. O f the t r o p o s p h e r i c inorganic species i n F i g u r e 1, N 0 , N O , and H O N O lack reasonably w e l l established, i n situ m e a s u r e m e n t t e c h n i q u e s that are r o u t i n e a n d p r o v i d e t i m e r e s o l u t i o n o n the o r d e r of m i n u t e s . T h e s e three species are a l l b e l i e v e d to p l a y i m p o r t a n t roles i n the a t m o s p h e r e , e v e n t h o u g h t h e i r concentrations are e x p e c t e d to b e no h i g h e r t h a n the l o w p p t r v to s u b - p p b v range outside u r b a n areas, b u t a p a u c i t y o f m e a s u r e m e n t s has p r e v e n t e d the f u l l verification of these roles. 3

2

i 5

T h e roles that these species play are a strong f u n c t i o n o f t h e i r p h o t o l y t i c and t h e r m a l stability. F u l l s u n l i g h t photodissociates N 0 a n d H O N O o n t i m e scales of seconds a n d tens of m i n u t e s , r e s p e c t i v e l y (17). N 0 t h e r m a l l y 3

2

5


266


dissociates to N 0 a n d N 0 o n a t i m e scale o f m i n u t e s at t e m p e r a t u r e s of the l o w e r troposphere. T h u s , the concentrations o f a l l t h r e e species are e x p e c t e d to reach significant levels i n the t r o p o s p h e r e o n l y at n i g h t , a n d t h e i r roles are expected to be significant o n l y d u r i n g this t i m e . A s i l l u s t r a t e d i n F i g u r e 10, n i g h t t i m e p r o d u c t i o n of H N 0 from b o t h N 0 a n d N 0 is possible. I n a d d i t i o n , N 0 reactions w i t h organic c o m p o u n d s are b e l i e v e d to be an i m p o r t a n t source of peroxy a n d h y d r o x y l radicals at n i g h t (69). T h e p r o p e r t i e s , a t m o s p h e r i c roles, a n d m e a s u r e m e n t s of N 0 a n d N 0 have b e e n extensively r e v i e w e d r e c e n t l y (70). I f significant sources are p r e s e n t , H O N O concentrations w i l l increase at n i g h t (or perhaps d u r i n g o t h e r l o w sunlight situations) a n d t h e n p r o v i d e a v e r y i m p o r t a n t source of O H radicals (71) after sunrise (or w h e n the sunlight i n t e n s i t y increases). T h e source of H O N O s h o w n i n F i g u r e 1 is c o m b i n a t i o n o f O H w i t h N O , w h i c h w i l l b e significant o n l y i n sunlit c o n d i t i o n s , b u t n o n p h o t o l y t i c sources have b e e n suggested: d i r e c t e m i s s i o n i n a u t o m o b i l e exhaust (72) a n d biomass b u r n i n g (73), c o n v e r s i o n o f N O o n w e t aerosols (reference 74 a n d references c i t e d therein), a n d heterogeneous h y d r o l y s i s o f N 0 o n surfaces o f p h y s i c a l objects (75). M e a s u r e m e n t t e c h n i q u e s for the troposphere for these t h r e e species r e q u i r e significant f u r t h e r w o r k . A s m e n t i o n e d i n p r e c e d i n g sections, N 0 a n d H O N O (but not N O ) have b e e n m e a s u r e d b y D O A S , b u t i n situ techniques are m u c h less w e l l d e v e l o p e d . N 0 has b e e n m e a s u r e d b y m a t r i x isolation e l e c t r o n s p i n resonance ( E S R ) (see references a n d discussion i n reference 70), b u t the t i m e r e s o l u t i o n is o f the o r d e r of an h o u r , a n d the m e t h o d is v e r y l a b o r - i n t e n s i v e . N o m e a s u r e m e n t s at a l l of N 0 have b e e n r e p o r t e d for the troposphere. D é n u d e r t u b e t e c h n i q u e s (references 76 a n d 77 a n d references c i t e d therein) have b e e n a p p l i e d to measure H O N O , b u t hydrolysis of N 0 o n the d é n u d e r c o l l e c t i o n surfaces, a n d perhaps o t h e r processes, e v i d e n t l y p r o d u c e artifact signals. A n i n t e r c o m p a r i s o n (78) b e t w e e n a dénuder system a n d a D O A S t e c h n i q u e i n d i c a t e d p o o r a g r e e m e n t at s u b - p p b v levels, w i t h the dénuder system g i v i n g h i g h e r levels. A n L I F m e t h o d is available for H O N O (79), b u t it suffers f r o m an i n t e r f e r e n c e associated w i t h a m b i e n t ozone. It w o u l d b e v e r y useful to d e v e l o p sensitive, r o u t i n e , i n situ methods for the m e a s u r e m e n t of all t h r e e species to verify t h e i r postulated roles a n d t r o p o s p h e r i c l e v e l s , a n d it w o u l d be p a r t i c u l a r l y useful i f these t e c h n i q u e s w e r e portable e n o u g h to d e p l o y o n aircraft w i t h a w i d e suite of other m e a s u r e m e n t s , because they are l i k e l y to e x h i b i t significant v e r t i c a l gradients. 2

3

3

3

2

5

3

3

2

5

v

2

3

2

s

3

2

5

2

Micrometeorological Flux Measurements.

It is important to q u a n -

tify the flux of the n i t r o g e n species to or from the a t m o s p h e r e d u e to surface e m i s s i o n or d e p o s i t i o n . M e a s u r e m e n t s of fluxes of N O a n d N 0 have b e e n m a d e b y enclosure t e c h n i q u e s , b u t the enclosures p l a c e d o n a surface m u s t b e suspected of d i s t u r b i n g the flux that t h e y are d e s i g n e d to measure. F l u x e s 2


9.

PARRISH & B U H R

267


also have b e e n d e t e r m i n e d f r o m measurements of v e r t i c a l c o n c e n t r a t i o n gradients; h o w e v e r , this t e c h n i q u e is o f l i m i t e d accuracy a n d a p p l i c a b i l i t y . A general t e c h n i q u e for d e t e r m i n i n g fluxes is to measure the c o r r e l a t i o n of fluctuations of concentration w i t h those of v e r t i c a l w i n d s p e e d , w h i c h are d u e to v e r t i c a l eddies i n the atmosphere (see reference 80 a n d references c i t e d therein). I f a species is e m i t t e d from the surface, for e x a m p l e , it is somewhat m o r e concentrated i n air parcels m o v i n g u p w a r d t h a n i n those m o v i n g d o w n w a r d . T o effect this approach r e q u i r e s sensors w i t h at least 1 H z , a n d preferably 10 H z , t i m e response. P r e s e n t l y , s u c h i n s t r u m e n t a t i o n is u n a v a i l a b l e , except for N O a n d NO m e a s u r e m e n t s . D e v e l o p i n g s u c h techniques for N 0 , N 0 (or N 0 ) , N H , a n d H N 0 w o u l d b e desirable. y

2

2

X

3

3

Development of Techniques for the Stratosphere.

Simultaneous

m e a s u r e m e n t of as m a n y of the n i t r o g e n species as possible w i t h h i g h spatial r e s o l u t i o n is a p o w e r f u l t e c h n i q u e for the stratosphere, j u s t as it is for the troposphere. F o r e x a m p l e , F i g u r e 11 shows data that w e r e c o l l e c t e d i n the polar stratospheric ozone studies. T h e figure shows the relationships b e t w e e n NO a n d N 0 i n the stratosphere, b o t h inside a n d outside the p o l a r vortices. G e n e r a l l y , the longer the air has b e e n i n the stratosphere, the l o w e r the N 0 a n d the h i g h e r the NO levels. T h i s b e h a v i o r occurs because N 0 reacts i n the stratosphere to y i e l d N O w i t h about a 7% net efficiency. T h i s reaction is the source of n e a r l y a l l the NO i n the stratosphere. O u t s i d e the p o l a r vortex regions NO is negatively correlated w i t h N 0 , a n d the 7% net y i e l d of NO is w e l l m a t c h e d b y the slope of the NO versus N 0 regression l i n e . y

2

y

2

2

y

y

2

y

y

2

I n F i g u r e 11 the N 0 levels are s h o w n to have c o n t i n u a l l y decreased as the aircraft passed i n t o each polar vortex, because air parcels that h a d spent progressively l o n g e r periods of t i m e i n the stratosphere w e r e b e i n g s a m p l e d . H o w e v e r , the NO levels d i d not c o n t i n u e to increase as w o u l d have b e e n expected; instead t h e y d r o p p e d p r e c i p i t o u s l y . T h i s b e h a v i o r i n d i c a t e d to the investigators that the N O h a d b e e n r e m o v e d f r o m the air i n the polar vortex. T h i s o b s e r v e d d e n i t r i f i c a t i o n was one strong c o n f i r m a t i o n for the models that p o i n t e d to heterogeneous c h e m i s t r y as the cause of the polar stratospheric ozone d e p l e t i o n that has b e e n i n t e n s i v e l y investigated i n the last few years. 2

y

y

C u r r e n t l y the v e r t i c a l profiles of the f u l l suite of n i t r o g e n species i n the stratosphere can b e m e a s u r e d r e m o t e l y from satellites, a n d m a n y total c o l u m n measurements can be o b t a i n e d f r o m the g r o u n d (see the p r e c e d i n g discussion). H o w e v e r , these results represent s u c h large spatial averages that m u c h of the p o w e r of simultaneous measurements is lost. I n situ speciation of the n i t r o g e n f a m i l y is r e q u i r e d . T o o b t a i n the r e q u i r e d spatial information d e m a n d s the adaptation of the m e a s u r e m e n t s to an aircraft p l a t f o r m . T h e n i t r o g e n species that are c u r r e n t l y of most interest i n the stratosphere a n d are c u r r e n t l y not m e a s u r e d b y s u c h i n situ, fast-response t e c h niques are N 0 , N O , H N 0 , C 1 0 N 0 , a n d H 0 N 0 . 2

2

s

3

2

2

2


268


O L J

I 80

I

I 120

I

I 160

I

' 200

'•

' 240

'

'280

N 0 (ppbv) 2

Figure 11. Rehtionship between NO and N 0 in the polar stratosphere. The curves are labeled with the potential temperatures; the lower potential temperatures correspond to lower altitudes and, in these cases, lower absolute temperatures. (Reproduced with permission from reference 85. Copyright 1990 Macmillan Magazines Ltd.) y

2

Chemical and Physical Characterization of Nitrogen-Containing Aerosol. N i t r o g e n - c o n t a i n i n g aerosols are i m p o r t a n t i n b o t h the t r o p o sphere a n d the stratosphere. T r o p o s p h e r i c aerosols c o n t a i n a m m o n i u m n i trate a n d p r o b a b l y other n i t r o g e n species (81). I n the stratosphere the aerosols that f o r m polar stratospheric clouds (PSCs) have b e e n f o u n d to contain n i t r i c a c i d (19, 82-84). T h e y are b e l i e v e d to p l a y essential roles i n the reactions i n the polar regions that release c h l o r i n e from the r e s e r v o i r species C 1 0 N 0 to f o r m the active C I forms that destroy 0 . F u r t h e r m o r e , the gravitational s e d i m e n t a t i o n of the aerosol removes the o x i d i z e d n i t r o g e n 2

3


9.

PARRISH & B U H R


269

species f r o m the stratosphere a n d p r e v e n t s the r e s e r v o i r species f r o m r e forming. T h e characterization of the c h e m i s t r y a n d physics of a t m o s p h e r i c aerosols is a science i n its infancy, a n d v i r t u a l l y the e n t i r e f i e l d is an o p e n challenge for analytical chemists. E v e n t e c h n i q u e s for p r o p e r l y c o l l e c t i n g samples of a t m o s p h e r i c aerosols n e e d d e v e l o p m e n t (see,

for e x a m p l e , reference

86).

S e v e r a l challenges specific to n i t r o g e n species can b e l i s t e d . F i r s t , v e r y little is k n o w n c o n c e r n i n g the organic nitrate c o m p o n e n t of aerosols. A s t u d y f r o m an u r b a n area r e c e n t l y a p p e a r e d (87) that indicates a p h o t o c h e m i c a l source for s u c h species. S e c o n d , the N O c o n v e r t e r measures some fraction o f the y

o x i d i z e d n i t r o g e n i n aerosols, b u t the fraction is v a r i a b l e a n d not w e l l c h a r a c t e r i z e d . T h i s v a r i a b i l i t y contributes to the difficulty i n c h a r a c t e r i z i n g the balance b e t w e e n the NO

y

m e a s u r e m e n t a n d the s u m of the i n d i v i d u a l l y

m e a s u r e d species (88). T h i r d , heterogeneous reactions o n aerosols m a y b e i n v o l v e d i n the transformations of gaseous species. T h e r e is e v i d e n c e for t h e reaction of N 0 2

5

o n w e t aerosols to y i e l d n i t r i c a c i d (89). It is of interest to

learn i f the aqueous-phase n i t r i c a c i d evaporates or r e m a i n s as p a r t i c u l a t e nitrate w h e n the aerosol dries or evaporates.

Summary T h e a p p l i c a t i o n of analytical c h e m i s t r y to the m e a s u r e m e n t o f a t m o s p h e r i c n i t r o g e n species is still a y o u n g f i e l d . I n situ m e t h o d s to m e a s u r e species that w e are not c u r r e n t l y able to measure r e l i a b l y ( H N 0 , 3

gaseous a n d

particulate organic nitrates, N 0 , N O , a n d H O N O i n the t r o p o s p h e r e a n d 3

N0 , 2

N 0 , HN0 , 2

5

3

2

s

C 1 0 N 0 , and H 0 N 0 2

2

2

i n the stratosphere) m u s t b e

d e v e l o p e d . E v e n for species that investigators b e l i e v e t h e y can m e a s u r e , a d d i t i o n a l methods s h o u l d be d e v e l o p e d , p a r t i c u l a r l y approaches w i t h defi n i t e specificity, r a p i d t i m e response, a n d g o o d spatial r e s o l u t i o n . T h e n these different methods m u s t be subjected to rigorous i n t e r c o m p a r i s o n s to e n s u r e that each is free of interferences a n d artifacts. T h e m e t h o d s , b o t h c u r r e n t and yet to be d e v e l o p e d , must be a d a p t e d not o n l y to surface f i e l d studies, b u t also to aircraft a n d b a l l o o n platforms. W e l l - d e s i g n e d field studies that s i m u l t a n e o u s l y measure as m a n y of these species as possible n e e d to b e c a r r i e d out. I n a d d i t i o n , n u m b e r s s h o u l d not s i m p l y be c o l l e c t e d ; the results m u s t be a n a l y z e d i n an i m a g i n a t i v e m a n n e r to gain as m u c h i n f o r m a t i o n as possible c o n c e r n i n g a t m o s p h e r i c p h o t o c h e m i c a l processes.

Acknowledgments T h e authors thank D a v i d F a h e y a n d F r e d F e h s e n f e l d for c r i t i c a l l y r e a d i n g p r e l i m i n a r y drafts of this m a n u s c r i p t a n d M i c h a e l T r a i n e r a n d J e r r y H a r d e r for m a n y h e l p f u l discussions a n d suggestions.


270


References 1. Isaksen, I. S. A . Tropospheric Ozone Regional and Global Scale Interactions; D . Reidel Publishing: Dordrecht, Holland, 1988; p 422. 2. Logan, J. A . J. Geophys. Res. 1989, 94, 8511-8532. 3. Calvert, J . G.; Lazrus, Α.; Kok, G . L.; Heikes, B. G.; Walega, J. G.; L i n d , J.; Cantrell, C. A . Nature (London) 1985, 317, 27-35. 4. 1990 Integrated Assessment Report; The U . S . National Acid Precipitation As sessment Program: Washington, DC, 1991. 5. Ozone Depletion, Greenhouse Gases, and Climate Change; National Academy: Washington, DC, 1989. 6. Mitchell, J . F. B. Rev. Geophys. 1989, 27, 115-139. 7. Logan, J. A. J. Geophys. Res. 1983, 88, 10,785-10,807. 8. Trainer, M.; Buhr, M. P.; Curran, C . M.; Fehsenfeld, F. C . ; Hsie, Ε. Y.; Liu, S. C . ; Norton, R. B . ; Parrish, D . D . ; Williams, E . J. J. Geophys. Res. 1991, 96, 3045-3063. 9. Atkinson, R.; Aschmann, S. M.; Carter, W. P. L.; Winer, A . M.; Pitts, J . N., Jr. J. Phys. Chem. 1982, 86, 4563-4569. 10. Platt, U.; Perner, D . ; Patz, H. W. J. Geophys. Res. 1979, 84, 6329-6335. 11. Hanst, P. L.; Wong, N. W.; Bargin, J. Atmos. Environ. 1982, 16, 969-981. 12. Schiff, Η. I.; Karecki, D . R.; Harris, G . W.; Hastie, D . R.; Mackay, G . I. J. Geophys. Res. 1990, 95, 10,147-10,153. 13. Finlayson-Pitts, B. J.; Pitts, J . N., Jr. Atmospheric Chemistry: Fundamentals and Experimental Techniques; John Wiley: New York, 1986; pp 319-347. 14. Sandholm, S. T.; Bradshaw, J . D . ; Dorris, K. S.; Rodgers, M. O.; Davis, D . D. J. Geophys. Res. 1990, 95, 10,155-10,161. 15. Schendel, J . S.; Stickel, R. E.; van Dijk, C . Α.; Sandholm, S. T.; Davis, D . D . ; Bradshaw, J . D . Appl. Opt. 1990, 29, 4924-4937. 16. Fredriksson, Κ. Α.; Hertz, Η. M . Appl. Opt. 1984, 23, 1403-1411. 17. Parrish, D . D . ; Norton, R. B . ; Bollinger, M. J.; Liu, S. C . ; Murphy, P. C . ; Albritton, D . L.; Fehsenfeld, F. C.; Huebert, B. J. J. Geophys. Res. 1986, 91, 5379-5393. 18. Parrish, D . D . ; Hahn, C . H.; Fahey, D . W.; Williams, E . J.; Bollinger, M. J.; Hübler, G . ; Buhr, M. P.; Murphy, P. C . ; Trainer, M.; Hsie, Ε. Y.; Liu, S. C . ; Fehsenfeld, F. C. J. Geophys. Res. 1990, 95, 1817-1836. 19. Fahey, D . W.; Kelly, Κ. K . ; Ferry, G . V . ; Poole, L. R.; Wilson, J . C . ; Murphy, D . M.; Loewenstein, M.; Chan, K . R. J. Geophys. Res. 1989, 94, 11,299-11,315. 20. Hoell, J. M., Jr.; Albritton, D . L.; Gregory, G . L.; M c N e a l , R. J.; Beck, S. M.; Bendura, R. J.; Drewry, J . W. J. Geophys. Res. 1990, 95, 10,047-10,054. 21. Webster, C. R.; May, R. D . J. Geophys. Res. 1987, 92, 11,931-11,950. 22. Webster, C. R.; May, R. D.; Toumi, R.; Pyle, J . A . J. Geophys. Res. 1990, 95, 13,851-13,866. 23. Farmer, C. B . ; Toon, G . C . ; Shaper, P. W.; Blavier, J . F.; Lowes, L. L. Nature (London) 1987, 329, 126. 24. Sanders, R. W.; Solomon, S.; Carroll, Μ. Α.; Schmeltekopf, A . L. J. Geophys. Res. 1989, 94, 11,381-11,391. 25. Solomon, S.; Miller, H. L.; Smith, J. P.; Sanders, R. W.; Mount, G . H.; Schmel tekopf, A . L.; Noxon, J. F. J. Geophys. Res. 1989, 94, 11,041-11,048. 26. Smith, J . P.; Solomon, S. J. Geophys. Res. 1990, 95, 13,819-13,827. 27. Coffey, M. T.; Mankin, W. G . ; Goldman, A . J. Geophys. Res. 1989, 94, 16,59716,613. 28. Wahner, Α.; Jakoubek, R. O . ; Mount, G . H.; Ravishankara, A . R.; Schmeltekopf, A . L . J. Geophys. Res. 1989, 94, 16,619-16,632.


9.

PARRISH

&

BUHR


271

29. Russell, J. M., III; Farmer, C . B.; Rinsland, C. P.; Zander, R.; Froidevaux, L.; Toon, G . C . ; Gao, B . ; Shaw, J.; Gunson, M . J. Geophys. Res. 1988, 93, 17181736. 30. Gunson, M . R.; Farmer, C. B . ; Norton, R. H.; Zander, R.; Rinsland, C. P.; Shaw, J . H.; Gao, B . - C . J. Geophys. Res. 1990, 95, 13,867-13,882. 31. Rinsland, C. P.; Toon, G . C . ; Farmer, C . B . ; Norton, R. H.; Namkung, J. S. J. Geophys. Res. 1989, 94, 18,341-18,349. 32. Report of the International Ozone Trends Panel: 1988; World Meteorological Organization: Washington, DC, 1988; Report No. 18; Global Ozone Research and Monitoring Project. 33. Kondo, Y.; Aimedieu, P.; Matthews, W. Α.; Fahey, D . W.; Murcray, D . G . ; Hofmann, D . J.; Johnston, P. V.; Iwasaka, Y.; Iwata, A.; Sheldon, W. R. Geophys. Res. Lett. 1990, 17, 437-440. 34. Kunde, V. G . ; Brasunas, J . C . ; Maguire, W. C . ; Herman, J . R.; Massie, S. T.; Abbas, M . M.; Herath, L . W.; Shaffer, W. A . Geophys. Res. Lett. 1988, 15, 1177-1180. 35. Blatherwick, R. D . ; Murcray, D . G . ; Murcray, F. H.; Murcray, F. J.; Goldman, Α.; Vanasse, G . Α.; Massie, S. T.; Cicerone, R. J . J. Geophys. Res. 1989, 94, 18,337-18,340. 36. Abbas, M. M.; Glenn, M. J.; Kunde, V. G.; Brasunas, J.; Conrath, B. J.; Maguire, W. C . ; Herman, J . R. J. Geophys. Res. 1987, 92, 8343-8353. 37. Fehsenfeld, F. C . ; Drummond, J . W.; Roychowdhury, U . K . ; Galvin, P. J.; Williams, E . J.; Buhr, M . P.; Parrish, D . D . ; Hübler, G . ; Langford, A . O.; Calvert, J . G.; Ridley, Β. Α.; Grahek, F.; Heikes, B. G . ; Kok, G . L.; Shetter, J. D . ; Walega, J . G.; Elsworth, C. M.; Norton, R. B . ; Fahey, D . W.; Murphy, P. C . ; Hovermale, C . ; Mohnen, V. Α.; Demerjian, K . L.; Mackay, G . I.; Schiff, Η. I. J. Geophys. Res. 1990, 95, 3579-3597. 38. Gregory, G . L.; Hoell, J . M., J r . ; Torres, A . L.; Carroll, Μ. Α.; Ridley, Β. Α.; Rodgers, M. O.; Bradshaw, J.; Sandholm, S.; Davis, D . D . J. Geophys. Res. 1990, 95, 10,129-10,138. 39. Fehsenfeld, F. C . ; Dickerson, R. R.; Hübler, G . ; Luke, W. T.; Nunnermacker, L . J.; Williams, E . J.; Roberts, J . M.; Calvert, J. G.; Curran, C. M.; Delany, A. C . ; Eubank, C. S.; Fahey, D . W.; Fried, Α.; Gandrud, B. W.; Langford, A. O.; Murphv, P. C . ; Norton, R. B.; Pickering, K. E.; Ridley, B. A. J. Geophys. Res. 1987, 92, 14,710-14,722. 40. Williams, E . J.; Sandholm, S. T.; Bradshaw, J . D.; Schendel, J . S.; Langford, A . O.; Quinn, P. K . ; L e B e l , P. J.; Vay, S. Α.; Roberts, P. D . ; Norton, R. B . ; Watkins, Β. Α.; Buhr, M. P.; Parrish, D . D . ; Calvert, J . G.; Fehsenfeld, F. C . J. Geophys. Res. 1992, 97, 11,591-11,611. 41. Gregory, G . L.; Hoell, J . M., J r . ; Carroll, Μ. Α.; Ridley, Β. Α.; Davis, D . D . ; Bradshaw, J.; Rodgers, M . O.; Sandholm, S. T.; Schiff, H . I.; Hastie, D . R.; Karecki, D . R.; Mackay, G . I.; Harris, G . W.; Torres, A . L.; F r i e d , A. J. Geophys. Res. 1990, 95, 10,103-10,127. 42. Gregory, G . L.; H o e l l , J . M., J r . ; Ridley, Β. Α.; Singh, Η. B . ; Gandrud, B . ; Salas, L . J.; Shetter, J . J. Geophys. Res. 1990, 95, 10,077-10,087. 43. Fox, D . L.; Stockburger, L . ; Weathers, W.; Spicer, C . W.; Mackay, G . I.; Schiff, H . I.; Eatough, D . J.; Mortensen, F.; Hansen, L . D . ; Shepson, P. B . ; K l e i n dienst, T. E.; Edney, E . O. Atmos. Environ. 1988, 22, 575-585. 44. Hering, S. V.; Lawson, D . R.; Allegrini, I.; Febo, Α.; Perrino, C . ; Possanzini, M.; Sickles, J . Ε., II; Anlauf, K. G . ; Wiebe, Α.; Appel, B. R.; John, W.; Ondo, J.; Wall, S.; Braman, R. S.; Sutton, R.; Cass, G . R.; Solomon, P. Α.; Eatough, D . J.; Eatough, N . L.; Ellis, E . C . ; Grosjean, D . ; Hicks, B. B . ; Womack, J. D . ; Horrocks, J.; Knapp, K. T.; Ellestad, T. G . ; Paur, R. J.; Mitchell, W. J.; Pleasant,


272

45. 46. 47. 48. 49. 50. 51. 52. 53. 54. 55. 56. 57. 58.

59.

60.

61. 62. 63. 64. 65. 66. 67. 68. 69. 70. 71. 72. 73. 74.


M.; Peake, E . ; MacLean, Α.; Pierson, W. R.; Brachaczek, W.; Schiff, Η. I.; Mackay, G . I.; Spicer, C. W.; Stedman, D . H.; Winer, A . M.; Biermann, H . W.; Tuazon, E . C. Atmos. Environ. 1988, 22, 1519-1539. Talbot, R. W.; Vijgen, A . S.; Harriss, R. C. J. Geophys. Res. 1990, 95, 75537561. Gregory, G . L.; H o e l l , J. M., J r . ; Huebert, B. J.; Van Bramer, S. E.; L e B e l , P. J.; Vay, S. Α.; Marinaro, R. M.; Schiff, Η. I.; Hastie, D . R.; Mackay, G . I.; Karecki, D . R. J. Geophys. Res. 1990, 95, 10,089-10,102. Papenbrock, T. H.; Stuhl, F. J. Atmos. Chem. 1990, 10, 451-469. Schlager, H.; Arnold, F. Geophys. Res. Lett. 1990, 17, 433-436. Darnall, K. R.; Carter, W. P. L.; Winer, A . M.; Lloyd, A . C . ; Pitts, J . N., Jr. J. Phys. Chem. 1976, 80, 1948-1950. Atkinson, R.; Lloyd, A . C. J. Phys. Chem. Ref. Data 1984, 13, 315-444. Liu, S. C. E O S , Trans., Am. Geophys. Union 1984, 65, 833. Shepson, P. B . ; Edney, E . O.; Kleindienst, T. E . ; Pittman, J . H.; Namie, G . R.; Cupitt, L. T. Environ. Sci. Technol. 1985, 19, 849-854. Stockwell, W. R. Atmos. Environ. 1986, 20, 1615-1632. Calvert, J. G.; Madronich, S. J. Geophys. Res. 1987, 92, 2211-2220. Atherton, C. S.; Penner, J . E . Tellus 1988, 40B, 380-392. Dlugokencky, E . J.; Howard, C. J . J. Phys. Chem. 1989, 93, 1091-1096. Roberts, J . M. Atmos. Environ. 1990, 24A, 243-287. Singh, H . B . ; Salas, L . J.; Ridley, Β. Α.; Shetter, J . D . ; Donahue, Ν. M.; Fehsenfeld, F. C . ; Fahey, D . W.; Parrish, D . D.; Williams, E . J.; Liu, S. C.; Hübler, G . ; Murphy, P. C. Nature (London) 1985, 318, 347-349. Gandrud, B. W.; Shetter, J. D.; Ridley, Β. Α.; Parrish, D . D . ; Williams, E. J.; Buhr, M . P.; Norton, R. B . ; Fehsenfeld, F. C . ; Westberg, Η. H.; Farmer, J. C . ; Lamb, Β. K . ; Allwine, E. J . EOS, Trans., Am. Geophys. Union 1986, 67, 884. Ridley, Β. Α.; Shetter, J . D.; Walega, J . G.; Madronich, S.; Elsworth, C . M.; Grahek, F. E.; Fehsenfeld, F. C . ; Norton, R. B . ; Parrish, D . D . ; Hübler, G . ; Buhr, M.; Williams, E . J.; Allwine, E . J.; Westberg, Η. H . J. Geophys. Res. 1990, 95, 13,949-13,961. Appel, B. R. J. Air Pollut. Control Assoc. 1973, 23, 1042-1044. Atlas, E . L . Nature (London) 1988, 331, 426-428. Buhr, M. P.; Parrish, D . D . ; Norton, R. B . ; Fehsenfeld, F. C.; Sievers, R. E.; Roberts, J . M. J. Geophys. Res. 1990, 95, 9809-9816. Flocke, F.; Volz-Thomas, Α.; Kley, D . Atmos. Environ. 1991, 25A, 1951-1960. Lloyd, A . C . ; Atkinson, R.; Lurmann, F. W.; Nitta, B. Atmos. Environ. 1983, 17, 1931-1950. Bandow, H.; Okuda, M.; Akimoto, H . J. Phys. Chem. 1980, 84, 3604-3608. Schuetzle, D . ; Cronn, D . ; Crittenden, A . L.; Charlson, R. J . Environ. Sci. Technol. 1975, 9, 838-845. Henderson, B. W. Aviat. Week Space Technol. 1990, 36, 36-38. Platt, U.; LeBras, G.; Poulet, G . ; Burrows, J. P.; Moortgat, G . Nature (London) 1990, 348, 147-149. Wayne, R. P.; Barnes, I.; Biggs, P.; Burrows, J. P.; Canosa-Mas, C. E.; Hjorth, J.; L e Bras, G . ; Moortgat, G . K . ; Perner, D . ; Poulet, G . ; Restelli, G . ; Side -bottom, H. Atmos. Environ. 1991, 25A, 1-203. Perner, D . ; Platt, U . Geophys. Res. Lett. 1979, 6, 917-920. Pitts, J. N., Jr.; Biermann, H. W.; Winer, A. M.; Tuazon, E . C. Atmos. Environ. 1984, 18, 847-854. Rondon, Α.; Sanhueza, E . Tellus 1989, 41B, 474-477. Notholt, J.; Hjorth, J.; Raes, F. Atmos. Environ. 1992, 26A, 211-217.


9.

PARRISH

&C

BUHR

Measurement Challenges of Nitrogen

Species

273

75. Pitts, J. N., J r . ; Sanhueza, E.; Atkinson, R.; Carter, W. P. L.; Winer, A . M.; Harris, G . W.; Plum, C . N . Int. J. Chem. Kinet. 1984, 16, 919-939. 76. Vecera, Z.; Dasgupta, P. K. Environ. Sci. Technol. 1991, 25, 255-260. 77. Kitto, A.-M. N.; Harrison, R. M. Atmos. Environ. 1992, 26A, 235-241. 78. Appel, Β. R.; Winer, A . M.; Tokiwa, Y.; Biermann, H . W. Atmos. Environ. 1990, 24A, 611-616. 79. Rodgers, M . O.; Davis, D . D . Environ. Sci. Technol. 1989, 23, 1106-1112. 80. Businger, J. Α.; Delany, A . C . J. Atmos. Chem. 1990, 10, 399-410. 81. Seinfeld, J. H. Atmospheric Chemistry and Physics of Air Pollution; John Wiley: New York, 1986; p 738. 82. Toon, Ο. B . ; Hamill, P.; Turco, R. P.; Pinto, J. Geophys. Res. Lett. 1986, 13, 1284-1287. 83. Pueschel, R. F.; Snetsinger, K. G . ; Goodman, J . K.; Toon, Ο. B . ; Ferry, G . V.; Oberbeck, V. R.; Livingston, J. M.; Verma, S.; Fong, W.; Starr, W. L.; Chan, K. R. J. Geophys. Res. 1989, 94, 11,271-11,284. 84. Gandrud, B. W.; Sperry, P. D.; Sanford, L.; Kelly, Κ. K . ; Ferry, G . V.; Chan, K. R. J. Geophys. Res. 1989, 94, 11,285-11,297. 85. Fahey, D . W.; Solomon, S.; Kawa, S. R.; Loewenstein, M.; Podolske, J . R.; Strahan, S. E.; Chan, K. R. Nature (London) 1990, 345, 698-702. 86. Huebert, B. J.; Lee, G . ; Warren, W. L . J. Geophys. Res. 1990, 95, 16,36916,381. 87. Mylonas, D . T.; Allen, D . T.; Ehrman, S. H.; Pratsinis, S. E . Atmos. Environ. 1991, 25A, 2855-2861. 88. Atlas, E . L.; Ridley, Β. Α.; Hübler, G . ; Walega, J . G.; Carroll, Μ. Α.; Montzka, D . D.; Huebert, B. J.; Norton, R. B . ; Grahek, F. E.; Schauffler, S. J. Geophys. Res. 1992, 97, 10,449-10,462. 89. Leaitch, W. R.; Bottenheim, J . W.; Strapp, J . W. J. Geophys. Res. 1988, 93, 12,569-12,584. RECEIVED

for review March 20, 1991.

ACCEPTED

revised manuscript June 22, 1991.


Measurement Challenges of Nitrogen Species in ... - ACS Publications

Recommend Documents