Formation of Aerosols by Reaction of Ozone with ... - ACS Publications

8 Formation of Aerosols by Reaction of Ozone with Selected Hydrocarbons

Downloaded by COLUMBIA UNIV on August 1, 2016 | http://pubs.acs.org Publication Date: June 1, 1972 | doi: 10.1021/ba-1972-0113.ch008

L . A . RIPPERTON and H . E. JEFFRIES Department of Environmental Sciences and Engineering, University of North Carolina, Chapel Hill, N . C. 27514 O. W H I T E Atomic Energy Commission, New York, Ν. Y. 10014

Dark phase reaction of ozone (O ) with open chain monoolefins in air produced no light-scattering aerosol detectable with the Goetz Moving Slide Impactor. Reactions of O with the cyclic olefins, cyclohexene andα-pinene,and the diolefin, 1,5-hexadiene (reactants in the low or fractional parts per million concentration) produced detectable quantities of light-scattering aerosols. Aerosol generation was enhanced by increasing concentrations of either reactant. Reducing oxygen from 20 to 2% reduced aerosol generation; in creasing water vapor concentration (~0.0, ~45, ~100% relative humidity, 21°C) enhanced aerosol generation. Ki netic data from the α-pinene-O system suggest that α-pinene reacted with a product of the original reaction. This copolymerization is proposed as an important step in forming organic particulate matter. 3

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T h e role of olefin-ozone ( O ) reactions i n generating aerosols from organic vapors and the influence of oxygen ( 0 ) and water vapor on aerosol production in these reactions have been studied here. Kinetic data were examined to try to derive a mechanism for forming aerosols from organic vapors. Past literature shows that organic compounds are important i n the formation and composition of aerosols (1, 2, 3 ) , but this information has not been widely accepted or used until recently. In 1963 Junge (4) i n cluded only a few sentences on the organic content of aerosols; however, 3

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219 Photochemical Smog and Ozone Reactions Advances in Chemistry; American Chemical Society: Washington, DC, 1972.

220

PHOTOCHEMICAL

SMOG AND OZONE REACTIONS

Goetz (5), writing about maritime haze particles, said that the degrading of particles by ultraviolet radiation "appears to be definite proof for the significant, if not occasional dominant, presence of various hydrocarbons in the aerocolloidal matter." H o w organic vapors are incorporated into the aerocolloidal mass is important in urban and in non-urban air. Polymeric material is generated when 0 reacts with liquid olefins, and aerosols also result from the reac tion of 0 with gas phase olefins at pressures in the millimeter range. This led to the belief that photochemical haze actually resulted from 0 reacting with olefins. Leighton (6) stated that early workers in air pollution chemistry found that olefins reacting with 0 in the low parts per million (ppm) concentrations did not produce aerosols. In contrast, Prager et al. (7) found that cyclopentene, cyclohexene, or 1,5-hexadiene in the ppm range reacting with 0 produce aerosols (hydrocarbon 10 ppm, 0 5 p p m ) . Photochemical systems containing N 0 and cyclic olefins or diolefins also produced aerosols. Studying 0 behavior in non-urban air, we followed up work of Went and Rasmussen (8) by considering the terpenes as possible gas phase destructive agents for atomospheric 0 —i.e., sinks for natural 0 . α-Pinene is the most abundant terpene found in the North Carolina pines (9, 10) and was the first terpene tested. No rate constant for the 0 - « pinene reaction was found in the literature; therefore, a study was made to determine it. The results of determining the utilization rate of the reactants suggested strongly that aerocolloidal material was produced. Went (11) reported that the reaction yielded an aerosol which was formed rapidly. W i t h reactants in the tens of parts per hundred million (pphm) range, we generated enough aerosol to produce a Tyndall beam in dark phase 0 -a-pinene reactions and in photochemical secondary 3

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Table I. Aerosol Production from Selected Hydrocarbon—Ozone Systems a

Hydrocarbon Compound

Ozone ppm

1 1.5 2.0 8.0 2.0 8.0 2

0.60 0.14 0.14 3.00 0.40 0.58 0.35

a-Pinene a-Pinene 1,5-Hexadiene 1,5-Hexadiene 1,5-Hexadiene Cyclohexane 2-Hexene a

Relative Light Scatter

Hydrocarbon Concentration ppm

Relative humidity =

0.01%

at

In Air

In Nitrogen (2% Oxygen)

2650 700 20 5000 0 0

21C°.

Photochemical Smog and Ozone Reactions Advances in Chemistry; American Chemical Society: Washington, DC, 1972.

— 90 70 — —

8.

RIPPERTON AND JEFFRIES

221

Formation of Aerosols

reactions of the system N 0 + α-pinene -f- hv (12,13,14). Placing freshly crushed pine needles i n the presence of 0 also generated aerosol. In 1969 Groblicki (15) reported that aerosol formed i n numerous 0 - o l e f i n (dark phase) and N 0 - o l e f i n (photochemical) systems i n the absence of S 0 . H e found little aerosol formed by reacting 0 with open-chained olefins such as 1-heptene but found much aerosol formed when 0 reacted with α-pinene and with cyclohexene i n low ppm of reactant concentration (4 p p m hydrocarbon). H e found that cyclopentene formed moderate amounts of aerosol and that 0 concentration seemed to be a limiting factor i n forming aerosol. From Groblicki's work and our study of the 0 - a - p i n e n e reaction, we believed that we had i n sight as to a mechanism of organic aerosol formation. A key step i n the process seems to be the forming of an intermediate diactive species. 2

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3

2

2

3

3

3


3

Recent publications by Altshuller (16), Mueller et al. (17), and Robinson and Robbins (18) study the more general aspects of aerosols in the ambient air.

Table II.

Effect of Cyclohexene Concentration on Aerosol Production

Reactants Cyclohexene, ppm

Ozone, ppm

Relative Light Scatter

0

0.60

0

0.5 1.0 1.6 2.4 3.2

0.60 0.60 0.60 0.60 0.60

0,

r 11 Q 1 3 2

U46 Î543 1025 1523 1453 521

«Air, R H = 0 . 1 % , 21°C.

Experimental

Generating Aerosols by D a r k Phase Ozone Reaction. Reactants, various hydrocarbons and 0 , were brought together i n low ppm or tenths of a ppm concentration i n 150-liter Teflon bags. The organic reactants used were α-pinene, cyclohexene, 1,5-hexadiene, cyclohexane, and 2-hexene. In all but one series of experiments, relative humidity was virtually zero (dew point N O + Ο 2

+ M ^ 0

Ο 3 + cyclohexene

(1)

+ M

(2)

> > > aerosol

(3)

3


8.

Table IV.

Compound Cyclohexanone Toluene 1,5-Hexadiene 1,5-Hexadiene Cyclohexanone + 1-Hexene a

225



Photochemical

Systems in A i r ( R H =

Concentration, ppm

N0 , ppm

5 5 7 7 5 (both)

0.0 0.1 0.0 0.5 0.0

0.1%)

Exposure Time, hr Relative Light Scatter

2

1 1 1 1 1

0 0 0 1,000 0

S u n l i g h t 1100-1500 hrs i n N o r t h C a r o l i n a ( F e b r u a r y ) .

In the mid-latitudes the midday sun would produce several pphm 0 from the radiation of 10 pphm of N 0 . W e therefore agree with Groblicki (15) that even in the photochemical systems it is the 0 - o l e f i n reactions and not the O-olefin reactions which produce aerosols from cyclic olefins. The quantitative data in Tables II and III, regarding the effect of varying 0 and cyclohexene, show that within limits producing aerosol depends directly on the concentration of both compounds. Decreasing molecular oxygen ( 0 ) concentration in the reaction mixture from 20% to 2 % decreases the particle formation (Table III). This indicates that incorporating 0 , perhaps as a peroxy radical, en hances the producing of aerosol. It might also indicate that 0 was re generated (see below). Water vapor at the time of particle formation greatly affected the reaction (Table I I I ) . There was an increase i n light-scattering, which visual microscopic examination suggested resulted from increased num bers of particles formed with increasing water vapor. In the humid runs particles were larger and coalesced more rapidly in the earlier reaction stages. This agrees with Goetz' finding (5) that the organic material


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Table V .

Conditions and Rate Constants for Pinene—Ozone Reactions

Run Number

o pphm

txPinene pphm

1 2 3 4 Average

4.1 4.0 22.8 26.5 —

64.9 105.8 101.7 122.1 —

0.088 0.202 0.179 0.129 0.15

α

3

a liter-moles^ R

pphm~

hr~

l

l

0.60 1.37 1.21 0.88 0.99

sec

Χ Χ Χ Χ Χ

10 10 10 10 10

5 5

5

5 5

a

Run Number

pphm,

$Pinene pphm

pphm~ hr~

5

2.4

94.9

0.058

R

l

l

liter-moles~

l

sec

3.94 Χ 10

4

C a l c u l a t e d f r o m i n i t i a l slope (runs 1, 2, a n d 3, 0 ) (runs 4 a n d 5 h y d r o c a r b o n ) . 3


226

PHOTOCHEMICAL


forms a film around the inorganic portion of the particle; the film resists coalescence. To orient the organic material into such a film takes a finite amount of time. Kinetic information on the reaction of 0 + α-pinene is given in Table V and Figures 1, 2, and 3. The value of the specific rate constant, using the data from the first few minutes of the reaction, is estimated to be 9.9 Χ 10 liters mole" sec" (0.15 pphm" h r " ) , assuming a second order reaction and a 1:1 stoichiometry. Along with other workers using open chain olefins (23), we d i d not find an adherence to 1:1 stoichiometry. Earlier workers had interpreted this as interference i n the 0 measurements from peroxides and possibly other oxidants produced i n o l e f i n - 0 reactions. However, i n this study the deviation from 1:1 stoichiometry can not be interpreted i n the same manner because the Regener-type chemiluminescence 0 meter is con sidered specific for 0 , and we assumed that our readings were as accurate 3

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1

1

1

1

3


3

3

3

1 0

1 5

1

1 10

1

1 15

1

1

Γ

20

TIME, MINUTES Figure 2.

a-Pinene utilization in ozone + a-pinene



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Δ EXPERIMENTAL — COMPUTER

Figure 3.

227


6.0 9.0 TIME, MINUTES

15.0

9.0 TIME, MINUTES

15.0

DATA POINTS

PLOT

Computer simulation in ozone + a-pinene

as the calibration. Also the ratio of α-pinene to 0 consumed per unit time varied from time to time (from — 1 to ^ 5 0 ) . If a 1:1 0 to a-pinene reaction is the first step i n the process being observed, the empirical data suggest that the α-pinene reacted with a product of the a - p i n e n e - 0 reaction. Numerous models were tested by computer simulation using numeri cal solution of a set of simultaneous differential equations and the one which best fitted the data was: 3

3

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0

3

+ αρ^(αρ—O )* x

ap + (ap—O )* -+(ap) Oa; x

2


(4) (5)

228

PHOTOCHEMICAL


( a p — 0 ) * —>R · + other products

(6)

X

R · + 20 -> R O · + 2

ri r r r fci k h ki 2

3

4

2

0

(7)

3

k (0 ) (ap) k (ap—0*)* (ap) k (ap—0 )* fc (R · ) (pseudo first order) 0.3 p p h m - h r - = 2.0 X 10 liter mole" 1.4 p p h m h r = 9.5 X 10 liter m o l e 96 h r - = 1.6 sec" 144 h r = 2.4 s e c (pseudo first order)

= = = = = = = =

3

2

3

X

4

1

1

5

1

- 1

- 1

5

-1

1

sec" sec

1

-1

1

- 1

-1

A mechanistic generation of 0 was needed because manipulation of the first models tested could not explain the behavior of the a-pinene and the 0 simultaneously. The rate constants were adjusted to force the computer simulation to fit the experimental data. Rate constant, k was determined to be about 0.15 pphm" h r (.—10 liter m o l e sec" ) using the data from the first ten minutes of reaction. However, because of the rapidity of the subsequent reactions, the actual rate might be somewhat greater, and it was adjusted to twice the determined value in the final model. The other rate constants, k , k , and Zc were originally estimated as 1.0 pphm" hr" , 48 h r , and 96 h r , respectively. Experience with the computer simula tion caused us to revise the values upward to fit the theoretical curve to the data. The final values accepted were 1.4, 96, and 144. Figure 3 shows the computer plot and the experimental data. This mechanism is suggested as a possible type of initiating series to generate aerosols from certain types of hydrocarbons. It is speculative but suggests reasons for the seemingly anomalous behavior of the reactants in the 0 -a-pinene reaction. The dimeric material in Step 2 above would be a precursor of the observed particles. Although open chain mono-olefins do not produce light-scattering particles they apparently produce particles less than 0.1 i n diameter. Both the system N 0 + α-pinene + hv (24) and photochemical systems con taining N 0 and open chain olefins—e.g. 1-hexene (25)—produced con siderable quantities of condensation nuclei. Figure 4 contains an infrared spectrum of the depositable aerosol formed i n the 0 -a-pinene reaction. Figure 4 also contains an infrared spectrum of local rural ambient aerosol. There are large differences i n the spectra; this agrees with Stephens (26) in comparing α-pinene aero sols with urban aerosols. Infrared spectra were obtained by Groblicki (15) for aerosol formed i n the systems N 0 + α-pinene -f- hv and N 0 + S 0 + α-pinene. The spectra obtained i n this laboratory for the 0 - a pinene system and Groblicki's N 0 + α-pinene + hv system were nearly


3

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l9

1

- 1

2

1

s

5

-1

1

1

4

1

1

3

2

2

3

2

2

2

3

2



1

3500

I

4000

2.5

3Ό

1

3000

35

Figure 4.

2500

I

MICRONS 40 60

I

1500

I

8Ό

I

1

1300

7.5

80

1

1200

1100

1

9.0

1000

1

100

i 900

1

800

MICRONS

Infrared spectra of deposit able (MSI) aerosols

2000

I

50


1

700

Ι5Ό

1

600

500

1

200

—I 400

25.0

230

PHOTOCHEMICAL

SMOG A N D OZONE REACTIONS

identical. This further supports Groblicki's suggestion that "the effects of reactant concentration and light intensity may be important only insofar as they affect the production of ozone" i n the photochemical system without S 0 . The similarity between Groblicki's photochemical aerosol from the system containing S 0 , N O , propylene, and (inadvertently) ammonia ( N H ) and these authors' ambient aerosol is striking. This similarity suggests that including S 0 and possibly N H i n reaction mixture pro duces a synthetic aerosol which resembles the natural more, at least i n IR spectra. Another series of experiments w i l l be run to study possibly incorporating less reactive compounds into the aerocolloidal mass by reaction with the diactive species postulated above. This type of system could produce I R spectra quite different from a simple 0 -a-pinene aerosol since different functional groups are included. 2

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Conclusions

The data reported here suggest that reactions between 0 and cyclic olefins and 0 and diolefins are important i n incorporating organic vapors into the aerocolloidal mass. W i t h i n limits aerosol generation, as measured by light-scattering from deposited material, was enhanced by increasing concentrations of each reactant ( 0 and cyclohexene), 0 ( 2 - 2 0 % ) , and water vapor (0-100% R H , 21°C). Comparing the behavior of open chained mono-olefins with cyclic and diolefins upon reaction with 0 suggested that the following processes are operative i n generating organic aerosols: 0 + cyclic olefin —> diactive species cyclic olefin + diactive species —» dimeric material —» aerosol. 3

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Acknowledgment

This study was supported by funds from National Science Foundation Grant GA-14475. The authors wish to thank the Glidden Paint Company for furnishing the α-pinene utilized in this study. Literature Cited 1. Goetz, Α., Preining, O., "The Aerosol Spectrometer and Its Application to Nuclear Condensation Studies," pp. 164-182, Monograph 5, NASNRC No. 746, American Geophysical Union, Washington, D. C. (1960). 2. Cadle, R. D., "Atmospheric Chemistry of Chlorine and Sulfur Compounds," pp. 18-21, J. P. Lodge, Ed., Waverly, Baltimore, 1959. 3. Wayne, L. G., "The Chemistry of Urban Atmospheres," pp. 185-200, Los Angeles County Air Pollution Control District Technical Progress Report, Vol. III, Los Angeles, 1962.



8.



231

4. Junge, C. E., "Air Chemistry and Radioactivity," pp. 178-180, Academic, New York, 1963. 5. Goetz, Α., "Microphysical and Chemical Aspects of Sea Fog and Oceanic Haze," Final Report to U. S. Navy Weather Research Facility, Norfolk, 1966. 6. Leighton, P. Α., "Photochemistry of Air Pollution," p. 174, Academic, New York, 1961. 7. Prager, M. J., Stephens, E. R., Scott, W. E., "Aerosol from Gaseous Air Pollutants," Ind. Eng. Chem. (1960) 52, 521-524. 8. Rasmussen, R. Α., Went, F. W., "Volatile Organic Material of Plant Origin in the Atmosphere," Proc. N.A.S. (1965) 53, 215-220. 9. Coker, W. C., Totten, H. R., "Trees of the Southeastern States," pp. 16-33, University of North Carolina Press, Chapel Hill, 1945. 10. Mirov, N. T., "Composition of Gum Turpentines of Pines," U. S. Depart ment of Agriculture, Forest Service Technical Bull. No. 1239, 1961. 11. Went, F. W., "Organic Matter in the Atmosphere and Its Possible Relation ship to Petroleum Formation," Proc. N.A.S. (1960) 46, pp. 212-221. 12. Jeffries, H. E., White, O., "α-Pinene and Ozone: Some Atmospheric Impli cations," Masters Thesis, University of North Carolina, Chapel Hill, 1967. 13. Ripperton, L. Α., Worth, J. J. B., "Chemical and Environmental Factors Affecting Ozone in the Lower Troposphere," Final Report: National Science Foundation, Grant GA-1022 (1969). 14. Lillian, D., "The Effect of Water Vapor on the Photochemical System NO + alpha-pinene + hv," Doctoral Dissertation, University of North Carolina, Chapel Hill, 1970. 15. Groblicki, P. J., Neble, G. J., "The Photochemical Formation of Aerosols in Urban Atmospheres," pp. 241-264, Charles S. Tuesday, Ed., American Elsevier, New York, 1971. 16. Altshuller, A. P., "Air Pollution," Anal. Chem. (1969) 41, 1R-13R. 17. Mueller, P. K., Kothny, E. L., Pierce, L. B., Belsky, R., Imada, M., Moore, H., "Air Pollution," Anal Chem. (1971) 43, 1R-15R. 18. Robinson, E., Robbins, R. C., "Emissions Concentrations, and Fate of Par ticulate Atmospheric Pollutants," Stanford Research Project SCC-5507, 1971. 19. Regener, V. H., "Measurement of Atmospheric Ozone with the Chemiluminescent Method,"J.Geophys. Res. (1964) 69, 3795-3800. 20. Jaffee, S., Loudon, R., ADVAN. CHEM. SER (1972) 113, 264. 21. Calvet, J. G , Pitts, J. N., Jr., "Photochemistry," p. 409, Wiley, New York, 1966. 22. Wayne, L. G., Bryan, R. J., Weisburd, M., Danchick, R., "Comprehensive Technical Report on all Atmospheric Contaminants Associated with Pho tochemical Air Pollution," pp. 4-57-4-58, Systems Development Corpora tion, Santa Monica, 1970. 23. Leighton, P. Α., Ibid., p. 161. 24. Lillian, D., Advan. Chem. Ser. (1972) 113, 211. 25. Decker, C. E., Page, W. W., "A Photochemical Study of Systems Containing Blends of Hexene-1, Nitrogen Dioxide and Sulfur Dioxide," Masters Thesis, University of North Carolina, Chapel Hill, 1965. 26. Stephens, E. R., Price, Μ. Α., "Smog Aerosol: Infrared Spectra," Science (1970) 168, 1584-1586. 2

RECEIVED May 24, 1971.


Formation of Aerosols by Reaction of Ozone with ... - ACS Publications

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