Environ. Sci. Techno/. 1982, 16, 254-262
precolumns. This work was supported by the U.S. Nuclear Regulatory Commission under Contract No. NRC-04-78275. Literature Cited (1) Davis, S.N.; Thompson, G. M.; Bentley, H. W.; Stiles, G. Ground Water 1980,18,14-23. (2) Thurman,E. M.; Malcolm, R. L.; Aiken, G. R. Anal. Chem. 1978,50,775-779. (3) Aiken, G. R.;Thurman, E. M.; Malcolm, R. L. Anal. Chem. 1979,51,1799-1803. (4) Koch, D.L.;Kissinger, P. T. Anal. Chem. 1980,52,27-29. (5) Creed, C. G.Res.lDev. 1976,279,40-44. (6) Cassidy, R.M.; Elchuk, S. J. Chromatogr. Sci. 1980,18, 217-223. (7) Saner, W. A.; Jadamec, R. T.; Sager, R. W. Anal. Chem. 1979,51,2180-2188.
(8) Simpson, R. L. J. Am. Lab. (Fairfield,Conn.) 1977,9,5, 109-115. (9) Gurkin, M.; Ripphann, J. Am. Lab. (Fairfield,Conn.) 1980, 12,5, 99-102. (10) Horvath, C.; Melander, W.; Molnar, I. Anal. Chem. 1977, 49,142-154. (11) Freiser, H.; Fernando, Q.“Ionic Equilibria in Analytical Chemistry”;Wiley: New York, 1963;Chapter 4. (12) Kirkland, J. J. Analyst (London) 1974,99,859. (13) Van Vliet, H. P. M.; Bootaman, Th. C.; Frei, R. W.; Brinkman, U. A. J. Chromatogr. 1979,185,483-495. (14) Pietrzyk, D. J.; Chu, C.-H. Anal. Chem. 1977,49,860-867. (15) Deming, S.N.; Turoff, M. Anal. Chem. 1978,50,546-548.
Received for review May 6,1981.Revised manuscript received December 21,1981. Accepted December 21,1981. Thk work was supported by the U S . Nuclear Regulatory Commission under Contract No. NRC-04-78-275.
Formaldehyde and Other Carbonyls in Los Angeles Ambient Air Daniel Grosjean
Environmental Research & Technology, Inc., 2625 Townsgate Road, Westlake Village, California 9 1361 From selective sampling and liquid chramatography analysis, ambient levels of carbonyl compounds as 2,4dinitrophenylhydrazoneshave been measured in the Los Angeles area during severe photochemical pollution episodes. Gas-phase concentrations and diurnal profiles are presented for six carbonyls: formaldehyde (up to 48 ppb), acetaldehyde (135ppb), propanal (114 ppb), butanal (17 ppb), 2-butanone (114 ppb), and benzaldehyde (11ppb). Also presented are particulate-phase concentrations and particle/gas distribution ratios for five carbonyls. Ambient carbonyl levels are discussed with respect to anthropogenic emissions and to photochemical production and removal in polluted air. Advantages and current limitations of the method employed are briefly discussed. H
Introduction
Of the major classes of organic compounds involved in photochemical air pollution, carbonyls (aldehydes and ketones) are of critical importance as products of the photooxidation of gas-phase hydrocarbons, as a major source of free radicals, and as precursors to organic-aerosol formation in urban air. Over the past several decades, considerable progress has been achieved, through both theoretical and experimental studies, in elucidating the chemical pathways involved in the formation and removal of carbonyl compounds in the atmosphere (1). The importance of carbonyls is reflected, for example, in the fact that detailed computer kinetic chemical models employed in oxidant (ozone) formation simulations and other regulatory applications all require formaldehyde and other carbonyls as data input (2). However, due to a large extent to analytical difficulties, measurements of ambient levels of carbonyl compounds have been limited to a few urban areas, and in most cases only formaldehyde and/or “total aldehydes” measurements have been performed. Using a method recently developed in our laboratory (3, 4 ) , we have performed measurements of ambient levels of carbonyl compounds in the Los Angeles area, under conditions of moderate to severe photochemical pollution, including the worst smog episodes encountered in 1980 in the Los Angeles air basin. 264
Envlron. Scl. Technol., Vol. 16, No. 5, 1982
Methods
The method employed in this study (3,4)entails the use of a selective reagent 2,4-dinitraphenylhydrazine(DNPH), which reacts with carbonyl compounds to form 2,4-dinitrophenylhydrazones (hereafter referred to as hydrazones) according to the reaction shown in Figure 1. After organic solvent extraction, the hydrazones are separated by high-pressure liquid chromatography (HPLC) and quantitated on the basis of their absorption at 360 nm. Quantitative aspects of the method including analytical recovery, sampling efficiency, reproducibility, and detection limits have been previously reported ( 3 , 4 )and only a brief description of the sampling and analytical protocols employed in this study is presented here. Samples were collected with microimpingers containing 10 mL of an aqueous, acidic (2 N HC1) solution of DNPH and 10 mL of a 9:l by volume mixture of cyclohexane and isooctane. In the absence of organic solvents, quantitative recovery is obtained for formaldehyde but not for other aliphatic and aromatic carbonyls (5). With organic solvents added, recoveries for these carbonyls are essentially complete and result from in situ extraction of the hydrazone in the organic phase, whose effect is to displace the aqueous-phase equilibrium (Figure 1)toward hydrazone formation. Detailed collection efficiency studies for formaldehyde, acetaldehyde, and benzaldehyde in the range of concentrations (a few micrograms) relevant to ambient-air sampling are described elsewhere (3,5). On several occasions, including nighttime sampling, an automated sampling device was employed as previously described (6). Typically, 60 L of ambient air was collected at a measured flow rate of -1 L mi&. Blanks were included with each batch of DNPH reagent and shipped to and from the field along with actual samples. Also included were control samples spiked with known amounts of acetaldehyde 2,4-dinitrophenylhydrazone. Samples, blanks, and controls were returned to the laboratory at low temperature in the dark and were stored at refrigerator temperature prior to extraction and HPLC analysis. After addition of an internal standard, extraction with a mixture of hexane and methylene chloride, and solvent
0013-936X/82/0916-0254$01.25/0
0 1982 American Chemical Society
NH-NH2 t
-
:;C-O
NOn
(DNPHj-L
0 0
H20tN02
NH-N=C’
Table I. Ambient Formaldehyde and Acetaldehyde Concentrations, California State University Los Angeles Campus, May-June 1980
H
sampling time
‘R
NO2 (2,4-DNP HYDRAZONE)
date
5/19
Figure 1. Reaction of carbonyls wlth DNPH to form 2,4dinitrophenyihydrazones.
5/ 21 5/22 5/27 5/28 5/29 6/17
07
F
P
;.1jJ 14
10
TIME
6
08
.05
5
.04
ta 22 > 3
03
6/18
02
.o 1
6/19
2
Figure 2. HPLC separation of selected carbonyl hydrazones: (A) formaldehyde; (6)acetaldehyde; (C) propionaldehyde; (D) methacrolein; (E) methyl vinyl ketone; (F) benzaldehyde; (G) glyoxal.
evaporation, the hydrazones were redissolved in methanol, separated with HPLC using reversed-phase columns and isocratic elution with methanol/water, and quantitated with an ultraviolet detector operated at a fixed wavelength of 360 nm. Calibration curves were constructed from stock solutions of the hydrazones of interest. A typical chromatogram showing good separation of the hydrazones of formaldehyde, acetaldehyde, and other aliphatic and aromatic carbonyls in less than 15 min is shown in Figure 2. A more detailed description of the method is given by Fung and Grosjean (4). Particulate-phase samples were collected by using 47mm diameter Teflon filters (Millipore FALP, 1-mm pore size) mounted on ERT’s sequential filter sampler equipped with a cyclone preseparator and operated for 4 h a t flow rates of 20 L min-l (sampler no. 1) and 40-70 L min-l (sampler no. 2). After being sampled, the filters were placed in glass test tubes containing aqueous acidic (2 N HC1) DNPH reagent, and the tubes were returned to the laboratory and stored at refrigerator temperature prior to HPLC analysis. Filter and aqueous reagent blanks were included and analyzed with each batch of field samples.
Results Ambient-air measurements were conducted a t two locations in the Los Angeles, CA, area. In May and June 1980, samples were collected on the roof of the nine-story science building on the California State University Los Angeles campus (CSLA), approximately 5 km east of the downtown area. In September and October 1980, measurements were conducted on the roof of the three-story Jacobs building on the Harvey Mudd College (HMC) campus, in Claremont, CA, approximately 50 km east of
6/20
(PDT) 12 :40-13:40 13 350-14:50 15 :02-16:02 9 :08-10:OS 11:ll-11~41 12:36-12:56 8:25-8:55 8: 30-9 :OO 10:09-10~59 11 :14-12~04 12:25-13:25 13:53-14:43 15:05-15:53 16 :12-17:02 17 :09-17:34 13 :09-13:54 14:03-14:48 14:59-15:44 15 :58-16:43 16154-17~39 17:56-18:42 18:51-19 :36 19 :45-20:30 10 :19-11 :04 11:10-12:05 12:22-13:07 13:18-13:53 14~07-14:52 15~04-15:49 16 ZOO-1 6 :45 17 :08-17:53 7:00-7:45 8 :18-8:48 9 :05-9 :35 9:52-10:22 10:37-11:07 11:17-11~47 11 :58-12:28
HCHO, CH,CHO, PPb ppb 21 33 40 0 2 26 32 10 5 3 6 3 27 7 33 3 13 6 34 7 16 8 21 6 19 4 11 11 22 10 31 24 26 4 28 6 16 11 12
27 39 19 18 22 24 23 6 10 10 16 21 11
6 11 19 11 9 11 9 3 7 2 6 9 12 8
20
32
15
Los Angeles. At CSLA, samples were collected during daytime under conditions of light to moderate photochemical smog. At HMC, samples were collected during daytime and nighttime, and included a set of consecutive 1-h and 2-h samples collected over a 36-h period, during severe photochemical smog episodes that included the worst episodes encountered in 1980 in the Los Angeles area. At CSLA, our study focused on formaldehydes and acetaldehyde, whose concentrations are listed in Table I. At HMC, other carbonyls were also included, and the corresponding results are listed in Table I1 and summarized in Table 111.
Discussion Carbonyls Identified and Ranges of Concentrations. Six carbonyls including formaldehyde (HCHO), acetaldehyde (CH3CHO),propanal (CH3CH2CHO),butanal (CH3CH2CH2CHO),2-butanone (or methyl ethyl ketone, CH3CH2COCH3),and benzaldehyde (C6H5CHO) were identified and quantitated. Acetone (CH3COCH3) was present in many samples but could not be quantitated due to microgram amounts of background impurity in the sampling reagent. In addition, many as yet unidentified carbonyls were present in samples collected during smog episodes. On the basis of their HPLC retention times (4), Environ. Sci. Technol., Vol. 16, No. 5, 1982
255
Table 11. Carbonyl Concentrations, Claremont, CA, September 19-October 8, 1980 sampling time date
(PDT)
9/19
08: 00-08~45 09 :OO-09:45 1 0 :00-10:47 11:01-11:46 11:58-1 2:46 1 3:OO-13:45 14:OO-14: 54 14: 56-15:45 15: 53-16:44 08:OO-08:55 09:12-1O:OO 10 :03-10:48 11:OO-11:46 12 :OO-12:47 1 3:03-13 :48 14 :OO-14 :45 1 5ZOO-15:47 16:OO-16:45 17:OO-17:55 18~05-18:47 19:OO-20 :OO 2o:oo-21:oo 21 :oo-22: 00 22 :OO-24:OO 0o:oo-02:oo 02:OO-04 :00 04:OO-06:OO 06:OO-08:OO 09:oo-1o:oo 10 :15-11:15 11:23-12:15 12~30-13~06 1 3:20-14 :04 14~08-15:08 15:12-16 :12 1 6 :13-17 :00 17:OO-18:OO 18:OO-19:OO 19:OO-19:45 09 :lo-10 :00 10:05-11: 00 11:oo-12:oo 12:OO-13:OO 1 3:OO-14:OO 14:00-1 5:OO 15:OO-16:OO 16 :OO-17 :00 1 7 COO-18 :00 18:00-19:00 19 :OO-2O:OO 08: 21-09: 00 09:oo-1o:oo 1o:oo-11: 00 11:oo-12:oo 12:OO-13:OO 1 3:00-14 :OO 14:OO-15:OO 1 5 :OO-16 :00 16:OO-17 :00 17 :OO-18: 00 11:oo-12: 00 1 2:04-13: 04 13:07-14 :07 14:lO-15:lO 1 5:13-15: 58 1o:oo-11 :oo 11:03-12:03 12:07-13:07 13:11-14:11 14:14-15:14
9/25
9/26
10/1
1012
1017
10/8
256
formaldehyde
acetaldehyde
9.6 22.9 10.1 12.0 11.7 12.7 7.9 15.7 6.9 20.0 22.0 22.3 24.0
3.8
Environ. Sci. Technol., Vol. 16, No. 5, 1982
5.6 7.8 6.4 6.2 2.9 6.0 3.3 4.7 10.0 11.2
pro pan a1
butanal
9.9 10.2 6.1 8.2 9.0 8.7 3.6 9.1 7.9
0.6 1.3 0.3 1.3 1.6 0.9 0.3 1.5 0.5 1.3 3.5 2.4 2.7 2.6 2.9 3.0 3.2 3.1 3.2 2.0
20.4 20.6 17.1 22.6 26.2 37.4 23.3 22.3 13.7 16.6 15.0 11.4 14.1 15.2 22.5 27.6 30.8 25.7 31.3 28.6 41.5 33.6 40.3 3.0 10.7 3.8 18.3 11.5 33.5 36.6 30.4 20.1 21.2 17.3 35.8 48.1 29.7 25.6 40.5 32.3 40.0 27.8 22.5 35.0 27.7 33.9 38.4 38.1 42.8 27.5 33.1 25.1 34.6
14.2 24.0 26.9 34.8 18.5 12.7 17.6 15.0 9.2 7.2 8.2 7.4 5.3 11.4 20.7 20.5 13.5 18.2 27.6 18.7 18.0 22.9 19.5 21.4 13.6 7.9 9.5 11.9 12.2 19.4 27.6 27.3 6.4 20.2 33.9 24.5 33.7 16.4 17.5 17.6 12.8 13.8 33.1 9.5 6.6 8.5 5.4 6.1 22.3 7.4 6.7 5.5 3.5 8.4
0.4 0.5 0.4
0.6 3.5 4.7
2.8 3.8 8.3 14.1 12.4
1.1 2.7
0.1 3.4 1.4
3.0 4.1 0.8 3.8 13.1 7.4 5.3 11.5 8.8 7.8 4.4 4.0
1.8 0.5 1.0 0.6 0.5 2.5 2.2 3.4 2.6 2.5 2.6
1.8
2.8 5.9 8.5 3.7 6.3 2.1 5.7
0.5 0.6 0.7 0.9 0.9 0.6 0.7 0.2
0.7 0.8 0.6 0.5 0.7 0.8 0.8 0.7 0.2
1.4 1.o 2.3 3.8 3.7 4.7 9.1 3.1 7.7 3.4 7.5 1.4 3.0
2.1 6.6 1.4 1.5
1.7 3.8 2.8 3.0 0.5 0.6 0.6 0.5 1.4 1.2 1.8 0.9 0.6 0.8
0.7 0.6 0.6 0.9
1.4 1.5 0.6 0.3 0.2 0.4 0.2 1.4 2.9 2.7 1.4 0.1 4.0 2.6 2.6 2.7 3.2 2.0 4.7
benzaldehyde
0.5
1.8
7.1
2-butanone (MEW
0.2 0.4 0.5 0.6 0.8 0.5 0.6 0.3 1.0 0.4 0.5 0.4
4.1 0.3 0.3
0.4 12.3
._
13.9 0.5
0.3 0.4 0.3 0.3 0.2 0.4 0.3
Table 111. Summary of Carbonyl Concentrations, Claremont, CA, September-October 1980 day 9/19 a9/25 time, PDT 8-17 8-24 no. of samples 9 15 range of carbonyl concentrations, ppb 8-23 11-37 formaldehyde 3-8 5-35 acetaldehyde 6-10 propanal 0.3-1.6 0.6-3.5 butanal 0-0.5 0-5 2-butanone 0-0.5 0-1 benzaldehyde 0.09 0.36 ozone (max), ppma 3.5 23 PAN (max), ppba a
loll
9/26 0-20 15
9-20 11
11-41 5-27 0.1-4.0 0-13 0-1 0.35 31
3-37 6-28 0-14 0.5-3.4 0-9 0-1 0.40 31
1012 8-18 10
1017 11-16 5
1018 10-15 5
17-48 12-34
28-38 5-22 0-8 0.5-1.4
25-43 3-8 0-6 0.6-2 0-14 0.2-0.4 0.38 46
0-7 0-8 0-1 0.46 44
0-0.4 0.38 47
Data from ref 24. 8-7
45-60 40-46 35-40
6-8 4-6 3-4
H\C;O H’
30-36 26-30 20-26
2-3
11-20 10-16
P n P
6-10 0-5 BELOW DETECTION
z
-
% C
K
a
0
n L
m
CH3-CH
0
14-18
0
2;c.
H 10-12 8-10
8-8
!
0
0.0
0.8 0.7 0.8 0.6 0.4 0.3 0.2 0.1
0
--0,s 1.0
0.0 0.8 0.7 0.8
0.4 0.3 0.2
0.1
BELOW DETECTION 4
8
12
18
20
NUMBER OF MEASUREMENTS
BELOW DE1 0
4
8
12
44
Number of Measurements Flgure 3. Frequency distributions of ambient levels of carbonyls (Claremont, CA, Sept-Oct 1980): formaldehyde, acetaldehyde, propanal.
these carbonyls may include monofunctional aliphatic and aromatic carbonyls and also polyfunctional carbonyls such as hydroxycarbonyls (4,7) whose positive identification would require mass spectrometry confirmation (8). At CSLA (Table I), formaldehyde concentrations in 28 samples ranged from 11to 39 parts per billion (ppb), and acetaldehyde concentrations ranged from 3 to 24 ppb (27 samples), both with significant diurnal variations. At HMC, formaldehyde was identified in virtually all samples at concentrations ranging up to 48 ppb, along with acetaldehyde (up to 35 ppb), propanal (up to 14 ppb), butanal (up to 7 ppb), 2-butanone (up to 14 ppb), and benzaldehyde (up to 1ppb). Concentrations reported for the aliphatic aldehydes propanal and butanal are computed with the assumption, on the basis of structure, solubility, reactivity with DNPH, and hydrazone stability considerations, that their collection efficiency is equal to that measured for acetaldehyde (5). Concentrations reported for 2-butanone are tentative, pending verification of the analytical recovery in our HPLC protocol and completion of ongoing collection efficiency studies for a number of ketones (9).Concentration-frequency distributions for the six carbonyls in Claremont air are given in Figures 3 and 4.
Flgure 4. Frequency distributions of amblent levels of carbonyls (Claremont, CA, Sept-Oct 1980): butanal, 2-butanone, and benzaldehyde.
Comparisonwith Other Urban Air Measurements. We have also measured carbonyl concentrations at several other locations in the Los Angeles area from July to October 1980. The results of these measurements will be reported later, along with results obtained during the 1981 smog season, and are entirely consistent with those reported here. Early measurements performed in the Los Angeles area in the 1960s were limited to formaldehyde, acrolein, and “total aliphatic aldehydes“, with reported formaldehyde levels of up to 150 ppb (10-12). A 1972 survey conducted in California reports daily averages of -35 and -20 ppb for formaldehyde and acetaldehyde, respectively (13). These results imply much higher 1-h averaged maximum concentrations for both carbonyls. Thus, levels of carbonyls in Los Angeles air appear to have decreased since the late 1960s and early 1970s. Our formaldehyde results are more in line with those recently reported (14-16)at several locations in the Los Angeles area using Fourier transform long-path infrared spectroscopy (FT IR). As is shown in Table IV, current formaldehyde concentrations in Los Angeles air (14-17) appear to be somewhat higher than those recently measured in other urban areas in the United States (18-19) and in Japan (20-23). For the other carbonyls, few data sets are available for comparison with our results. Acetaldehyde concentrations Envlron. Sci. Technol., Vol. 16, No. 5, 1982
257
Table IV. Comparison with Other Studies Conducted in Urban Areas maximum concentrations, ppb total aldehyde HCHO
ref
CH, buta- 2-buta- PhCHO acrolein propanal nal none CHO
Los Angeles, CA, Area
Los Angeles, July-Nov 1960 Los Angeles, Sept-Nov 1961 Huntington Park, Oct 1968 El Monte, Oct 1968 Riverside, July -0ct 1977 Claremont, Oct 1978 CSLA, May-June 1980 CSLA, May-June 1980 Claremont, Sept-Oct 1980 other sites in Los Angeles area, JUly-Oct 1980 Newark and Bayonne, NJ, June-Aug 1972-1974 Houston, TX, summer 1977 Nagoya, Japan, Dec 1976 Osaka, Japan, May-July 1978 (six samples) Tokyo, Japan, 1974 Tsu kuba, Japan, 1979
10 11 12 13 14 15
360 -150 173 148
17
130 150 136 90 38 71 40 71 48 70
18
Other Urban Areas 20
this work 16
this work
19 20 21
51
22 23
58
of up to -10 ppb have been reported in urban areas in Japan (20-21). According to a recent National Academy of Sciences report ( I ) , ambient concentrations of benzaldehyde have not been reported prior to our work. Propanal (0.4 ppb) has been previously found in two samples collected in 1978 in Osaka, Japan (21). To our knowledge, urban levels of butanal and of methyl ethyl ketone have not been reported Grior to this work. Diurnal Variations. Time-concentration profiles for all carbonyls at HMC were consistent with those expected at a smog receptor site several hours downwind from the downtown Los Angeles area, with maxima at the t2me the smog fronts reached Claremont in the late afternoon. These diurnal variations are shown in Figure 5 for the September 25-26, 1980, smog episode. Also shown in Figure 5 are the corresponding diurnal variations of ozone (maxima 350 ppb on both days) and of peroxyacetyl nitrate (PAN), the latter measured by our group as part of a study of the distribution of nitrogenous pollutants during smog episodes (24). Relative Ambient Concentrations and Emission Rates. I t has generally been assumed in a number of previous studies ( I ) that formaldehyde accounts for up to 7040% of the total aldehydes in urban air and that anthropogenic emissions of carbonyls are dominated by automotive sources. However, as more refined carbonyl emission inventories for both stationary and mobile sources (the latter including exhaust from catalyst-equipped cars and from lighbduty diesel vehicles) have become available (I), it appears that the above concepts should be somewhat revised. For example, exhaust acetaldehyde to formaldehyde ratios are significantly higher for catalystequipped cars than for cars without catalytic converters (1). In addition, the contribution of stationary sources appears to be more significant than was previously assumed. According to a 1974 emission inventory compiled by the California Air Resources Board and employed until at least late 1980 for modeling purposes, the formaldehyde emission rate in the California South Coast Air Basin is -20 X lo3 kg/day, of which -11 X lo3 kg/day, or 55% of the total, are associated with automotive sources. Emission rates for acetaldehyde, acetone, and methyl ethyl ketone, each -17 X lo3 kg/day, are nearly equal to that 258 Envlron. Scl. Technol., Vol. 16, No. 5, 1982
11 14 8 8
24 35 37
14 14
10 8
0.4
7
14 15
8
1
2
13 34 24 10
n n
i 0
1
12
I8
11
Q/2S
I
1P
,I
I,
9/26
TIME, PDT
Figure 5. Diurnal profiles for 03, PAN, and selected carbonyls (Claremont, CA, Sept 25-26, 1980). Solid and dashed lines connect consecutive and nonconsecutive 1-h carbonyl samples, respectively. Concentrations of benzaldehyde and propanal, not shown here, exhlblted the same diurnal varlatlons (see Table 11).
of formaldehyde. These emission rates are consistent with our ambient measurements, where formaldehyde is seen to account for a significant, but not overwhelming, fraction of total ambient carbonyl. Photochemical Production and Removal of Carbonyls. In addition to anthropogenic emissions, carbonyls are formed in urban atmospheres as products of aliphatic and aromatic hydrocarbon photooxidation. In turn, photochemical processes, including photolysis and reaction with the hydroxyl radical, are major removal pathways for atmospheric carbonyl compounds. Both photochemical formation and removal are expected to be important during the smog episodes studied in this work, and a qualitative indication of the extent of photochemical removal of aldehydes is given in Figure 5, where concentration of PAN and of acetaldehyde, the major precursor of PAN in photochemically polluted air, are seen to be nearly equal. Figure 6 shows ozone concentration profiles for the September 25-26 smog episode at Los Angeles, Upland (near our Claremont site), and Palm Springs and illustrates the conditions of poor ventilation along with
02 0 1
En 0 3o d O
0.2 0.1
0 0 1
0 8
12
16
Sept -52
20
24
8
4
Sept 2 6 Tlme
12
18
20
24
WSept 2 7
PST
Flgure 6. Ozone diurnal profiles for downtown Los Angeles, Upland, and Palm Springs, Sept 25-26, 1980.
high temperatures (130 "C) encountered during the period studied and conductive to severe photochemical pollution. So that the relative contribution of direct emissions and photochemical processes to the measured ambient carbonyl levels could be further investigated, carbon monoxide measured at nearby Upland was employed as a tracer, and carbonyl compound to CO ratios were calculated. The diurnal variations of these ratios during the September 25-26 36-h period of continuous carbonyl measurements are shown in Figure 7. Two distinct periods of photochemical activity are seen to be associated with nearby morning emissions and with the smog fronts reaching Claremont in the late afternoon. During these two periods, carbonyl compound to CO ratios increase from low values of -2-3 x to maxima of 8-10 X Carbon monoxide emission rates for the south coast air basili are -8 X 106kg/day, from which we derive formaldehyde/CO and acetaldehyde/CO emission rate ratios of 2.5 X low3and 2.1 X respectively. These ratios are consistent with the ambient level ratios shown in Figure 7 for nighttime and early-morning samples, i.e., in the absence of significant
photochemical activity. Extrapolating the increase in daytime carbonyl compound to CO ratios measured in Claremont to the entire Los Angeles area (not necessarily a bad assumption for the stagnation conditions illustrated in Figure 6 and often associated with multiday smog episodes), we can estimate net (i.e., formation minus removal) atmospheric photochemical production rates for carbonyls to be as high as -80 X lo3 and -60 X lo3 kg/day for formaldehyde and acetaldehyde, respectively. Combining these production rates with those for the higher molecular weight carbonyls acetone, 2-butanone, propanal, butanal, and benzaldehyde, we estimate total net photochemical production rates in excess of 200-250 X lo3 kg/day for carbonyls in the Los Angeles basin on smoggy days. Although large uncertainties are admittedly associated with these estimates, they underline the significant role of carbonyls in urban photochemical pollution. Particulate-Phase Measurements. Two sets of particulate-phase measurements involving the collection of consecutive 4-h samples on Teflon filters were conducted on September 2Fr26 (36 h) and October 1-2 (24 h). Of the six carbonyls identified in the gas phase in Claremont air, five were also found in the particulate phase (Table V). Benzaldehyde was not found at the detection limit afforded by our method [ -6 ng (4), which translates to 1.2 ng m-3 and 0.35-0.6 ng m-3 for the samples collected on September 25-26 and October 1-2, respectively.] Diurnal variations shown in Figure 8 do not reveal well-characterized profiles, although maxima were usually observed in the morning and/or late afternoon along with the corresponding maximum gas-phase concentrations and/or formation rates (compare with data in Figures 5 and 7). Although easily measurable in view of the large volume of air sampled, the particulate-phase concentrations of the five carbonyls were small, ranging up to 0.26 pg m9 for formaldehyde and propanal, 0.4 pg m-3 for acetaldehyde,
9/25 TIME, PDT 9/26 Figure 7. Diurnal varlatlons of CO, 03, PAN, and the forrnaldehyde/CO and acetaldehyde/CO ratlos (Claremont, CA, Sept 25-26, 1980). Solld and dashed lines connect consecutive and nonconsecutlve aldehyde samples, respectively.
Envlron. Sei. Technol., Vol. 16, No. 5, 1982 259
Table V. Carbonyl Concentrations, Particulate Phase (pg m-3) date 9/25
9/26
1011
1011-10/2 1012
sampling time 08:OO-12 :00 12:OO-16:OO 16:00-2O:OO 2O:OO-24 :00 00 :OO-04 :00 04 :OO-08:OO 08 :OO-12 :00 12:OO-16 :OO 16:OO-19:40 1O:OO-13 :30 1 3 ~ 3 0 - 1 7:30 1 7 :30-21: 30 21:30-01~30 01 :30-05:30 05:30-09: 30
8
volume sampled, m3 5.08 5.08 5.08 5.08 5.08 5.08 5.08 5.17 5.17 16.18 13.94 12.70 9.86 10.55 17.76
12
16
9/25
flow rate,
L/min 21.1 21.1 21.1 21.1 21.1 21.1 21.1 21.5 21.5 77.01 66.31 52.91 41.1 44.0 74.1
20
24
formaldehyde 0 0.146 0.264 0 0.176
acetaldehyde 0.064 0.318 0.140 0.106 0.048
propanal 0.004 0 0.044 0.080 0
butanal 0 0 0.042 0.060 0.018
2-butanone 0.068 0 0.082 0.090 0.062
0.180 0.172 0.082 0.018 0.038 0.002
0.406 0.020 0.016 0.022 0.060 0.048
0 0 0 0.011 0.180 0.268
0 0.098 0.026 0.007 0.009 0
0.110 0.098 0 0.006 0.024 0.055
0 0.007 0.007
0.032 0.038 0.002
0.027 0.022 0
0.013 0.010 0
0.030 0.018 0.013
4
12
TIME, PDT
8
16
20 9/2 6
Flgure 8. Diurnal varlations of carbonyl particulate-phase concentrations &g m-3), temperature (“C), and humidity (%) (Claremont, CA, Sept 25-26, 1980). Solid and dashed lines connect consecutive and nonconsecutive samples, respectively.
and -0.1 pg m-3 for butanal and 2-butanone. Thus particulate-phaselgas-phase concentration ratios listed in Table VI are t y p i d y less than i.e., -99% of the total aldehyde mass concentration is found in the gas phase and only -1% in the aerosol phase, However, even these small aerosol-phase concentrations appear to be much higher than those predicted on the basis of a simple equilibrium between aqueous (aerosol droplet) and gas phases. From 280
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the analysis of Klippel and Warneck (%), droplet carbonyl concentrations can be estimated from the relation c1 = HC,W where C1and C, are the carbonyl concentrations in the aerosol droplet and in the gas phase, respectively, W is the mass concentration of water in the aerosol droplet, and H is Henry’s law coefficient for the carbonyl of interest. In
Table VI. Ratios of Particulate-Phase/Gas-Phase Carbonyl Concentrations during Smog Episodes, Claremont , CA, September-October 1980 103P/G ratios" date
9/25
9/26
time (PDT)
08 ZOO-12:OO 12:OO-16:OO 16:OO-20:00 2O:OO-24:OO 00:00-04:00 04:OO-08:00 08 :OO-12:00 12:OO-16:OO 16:OO-19~40 10:00-13:30 13:30-17:30 17:30-21:30
formaldehyde
Ob 6.3 7.8 0 10.8
. . .C
acetaldehyde
4.1 9.1 3.4 4.6 3.5
...
propanal
butanal
2-butanone
*..
0 0 5.8 20.7 20.0
11.0
... ...
... ... ... *.. ... ... *.. 0.1 ...
21.6 12.7
... ...
...
0 14.5 16.6 4.5 3.4 0 10/1 3.3 1.4 3.0 0 3.3 " Ratio of particulate-phase (P, pg m-3) to gas-phase (G, pg m 9 )carbonyl concentrations. 0 = no measurable particulate . . . = gas phase concentration not measured over particulate phase sampling period. phase concentrations. 5.4 4.9 1.7 2.0 1.2 0.1
the case of formaldehyde, H = 1.8 X lo-' m3pg-l at 20 OC when C,,C,, and W are expressed in pg m-3 (26). As a typical example relevant to this study, we take C, = 25 pg m-3 (-20 ppb) and W = 15% of the aerosol mass concentration, which we set at 150 p g m-, for a smoggy day in Los Angeles. Thus W = 22.5 pg m-,, from which we pg m-3 and Cl/C, as -4 X lo4, estimate C1as -0.1 x Le., -3 orders of magnitude less than the measured formaldehyde particulate-phase concentrations (Table V) and particle/gas concentration ratios (Table VI). The same conclusions apply to the other carbonyls, for which similar calculations can be carried out. Obviously, the simple gas-aqueous droplet equilibrium model does not fit our data, and this may be due to several factors, including the following: (a) aqueous droplet concentrations are beyond those that can be adequately described by simple dilute solution models; (b) the presence of an organic film modifies considerably the gas-droplet interface (e.g., mass transfer coefficients, etc.); (c) the equilibrium is displaced by aerosol-phase reaction of carbonyls to form unstable adducts (e.g., with SOz, NH,, etc.) from which the free carbonyl is in turn displaced by DNPH reagent; (d) the reported particulate-phase concentrations result from retention of gaseous aldehyde on the collection substrate (filter artifact). Experiments were conducted in the field with Teflon filters subjected to passive exposure to ambient air for up to 34 h, and no measurable amounts of carbonyls were found in these conditions. In another set of experiments, ambient particulate samples (4h X 20 L mi&) were collected in Claremont with two Teflon filters mounted in series. Analyses of the bgckup filters again revealed no measurable amounts of carbonyls in the range of carbonyl concentrations [temperature (57-96 OF), humidity (15-96%)] listed in Tables VI and VI1 or under the range of air-quality conditions encountered in Claremont during this study. These results appear to rule out the possibility of artifact formation on the Teflon filter itself, in contrast to those of Klippel and Warneck (25) for formaldehyde on glass-fiber filters. However, gaseous carbonyls could be retained by adsorption on the layer of deposited particulate matter during sampling, but one would assume that these conditions would also be conducive to removal of the adsorbed carbonyl by heterogeneous oxidation to carboxylic acids. These and other aspects of carbonyl accumulation in particulate matter will warrant further investigations. Advantages and Current Limitations of the Method. Of the several methods developed over the years
12.9 0.6 0.5 1.2 1.9 1.5
Table VII. Acetaldehyde Hydrazone Stability in Spiked Impingers Exposed to Ambient Polluted Air ambient pollutant levels, ppbb
date
6/18 6/19 6/19 6/19
start time (PDT)= NO,
13:lO 10:19 15:05 17:OO
70 120 90 80
hvdrazone
0,
recovery, pgc
125 115 170 65
1.11 1.36 1.31 1.15
Av 1.23 * 0.12 (100i: 10%) a Samples collected at CSLA for 45 min at a flow rate of 1 L min-'. Two impingers containing 10 mL of aqueous acidic (2N HCl) DNPH reagent plus 10 mL of a 9:l by volume mixture of cyclohexane and isooctane were operated in parallel. One impinger was spiked with 1.23 pg of the 2,4-dinitrophenylhydrazoneof acetaldehyde. The Averaged over second impinger was used as a control. the sampling period. Other ambient pollutants included hydrocarbons, aldehydes (see Table I), sulfur dioxide, Difference, after nitric acid, PAN, free radicals, etc. reagent blank substraction, between acetaldehyde hydrazone concentrations measured after sampling in the spiked and the control impingers.
for trace carbonyl measurements, the method developed in our laboratory and involving sampling with DNPH reagent and analyzing with HPLC appears to have distinct advantages. At its present stage of development, the method is suitable for the determination of not only formaldehyde but also a number of other carbonyls in air, does not involve significant equipment investmefit, and is suitable for cost-effective application to field studies, including urban and regional networks. The simplicity of the sampling equipment required makes this method attractive for aircraft sampling and for studies conducted at rural and remote sites as well as in urban areas. The method employed in this study has the potential to be expanded, with use of mass spectrometry for confirmation of the carbonyl molecular structure (8),to a large number of mono- and polyfunctional carbonyls, both aliphatic and aromatic. Because DNPH reacts specifica'lly with carbonyls and since each carbonyl hydrazone is separated by HPLC, the potential for interferences appears to be minimal. Lowe et al. (26)have verified that two major pollutants, ozone (up to 100 ppb) and sulfur dioxide (up to 90 ppb), did not Environ. Sci. Technol., Vol. 16, No. 5, 1982
261
interfere with formaldehyde sampling using DNPH reagent. Additional interference studies with PAN and other oxidants are in progress in our laboratory. We have previously shown (5) that the presence of other aldehydes in the matrix air had no effect on the recoveries of formaldehyde, acetaldehyde, and benzaldehyde, an expected result since DNPH reagent is employed in large excess of ambient carbonyl levels. Control experiments with impingers spiked with acetaldehyde hydrazone and exposed to ambient air at CSLA yielded recoveries of -100% (Table VII), this indicating that, once formed, the hydrazone was stable when exposed to ambient air containing up to -150 ppb of NOz and -200 ppb of ozone, as well as hydrocarbons, free radicals, SOz, and other pollutants. Current limitations are due mostly to background carbonyl impurities in the DNPH reagent and solvents employed. The effect of these impurities is to restrict detection limits to -0.1-2 ppb (depending upon the reagent batch and the carbonyl studied) instead of achieving the -10-50 ppt detection levels afforded by the analytical method (5). A more effective reagent cleanup protocol has been recently developed (6) and will be employed in future studies.
Conclusions Measurements of carbonyl compounds in Los Angeles air were performed during conditions of moderate to severe photochemical smog. Of the carbonyls identified and quantitated in this study, several are believed to be reported for the first time. From a combination of the aldehyde data set reported here with data concerning PAN, nitric acid, and other pollutants measured as part of a companion study (24),a detailed experimental data base concerning major photochemical pollutants is now available for severe smog episodes at a downwind site in the Los Angeles area and may serve as reference for computer modeling or other applications. The method used in this study is currently being applied in our laboratory to additional studies of ambient levels of carbonyls in the Los Angeles and other areas, to specific measurements in industrial atmospheres, and to atmospheric chemistry investigations conducted in laboratory and environmental chamber experiments. Acknowledgments
I express my gratitude to Joseph Bragin at California State University, Los Angeles, and to Gregory Kok and Joyce Nutall at Harvey Mudd College, Claremont, for their hospitality and logistical support. At ERT, Delores Youtz and Daniel Womack had major responsibility in the CSLA and HMC field operations, respectively, and HPLC analyses were performed by Robert Swanson. Julian Foon of the Southern California Air Quality Management District provided air-quality data for Upland and other SCAQMD stations. Helpful comments from Philip Hanst and Bruce W. Gay, Jr., of the U.S.EPA, Gregory Kok of HMC, Kochi Fung and Fred Lurmann of ERT, and the
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members of the CRC CAPA-17 Project Group (Alan Dunker, chairman) during the course of this study are much appreciated.
Literature Cited (1) Board on Toxicology and Environment Health Hazards; "Formaldehyde and Other Aldehydes"; National Academy Press: Washington, D.C., 1981. (2) Carter, W. P. L.; Winer, A. M.; Pitts, J. N., Jr. Atmos. Environ. 1982, 16, 113. (3) Grosjean, D.; Fung, K.; Atkinson, R. Paper no. 80-50.4,73rd Air Pollution Control Association Annual Meeting, Montreal, Quebec, June 22-27, 1980. (4) Fung, K.; Grosjean, D. Anal. Chem. 1981,53, 168. (5) Grosjean, D.; Fung, K., Anal. Chem., in press. (6) Fung, K.; Swanson, R.; Grosjean, D. Paper no. 81-47.1,74th Air Pollution Control Association Annual Meeting, Philadelphia, PA, June 21-26, 1981. (7) Fung, K.; Grosjean, D., submitted for publication. (8) Grosjean, D., submitted for publication. (9) Grosjean, D.; Swanson, R.; Fung, K., to be submitted for publication. (10) Renzetti, N. A.; Bryan, R. J. J. Air Pollut. Control Assoc. 1961, 11, 421. (11) Altschuller, A. P.; McPherson, S. P. J . Air Pollut. Control Assoc. 1963, 13, 109. (12) Stahl, Q. R. Air Pollution Aspects of Aldehydes, National Technical Information Service No. PB 188081, Springfield, VA, 1969. (13) California Air Resources Board Staff Report, Sacramento, CA, 1972. (14) Tuazon, E. C.; Winer, A. M.; Graham, R. A.; Pitts, J. N., Jr. Adv. Environ. Sci. Technol. 1980, 10, 259-300. (15) Tuazon, E. C.; Winer, A. M.; Pitts, J. N., Jr. Enuiron. Sci. Technol. 1981,15, 1232. (16) Hanst, P. L., personal communication. (17) Grosjean, D.; Swanson, R. D., unpublished results. (18) Cleveland, W. S.; Graedel, T. E.; Kleiner, B. Atmos. Environ. 1977, 11, 357. (19) Houston Area Oxidant Study Aldehyde Monitoring Program, Radian Corp., Austin, TX. National Technical Information Service No. PB-283229, Springfield, VA, April, 1978. (20) Hoshika, Y. J. Chromatogr. 1977, 137, 455. (21) Kuwata, K.; Uerobi, M.; Yamaasaki, Y. J. Chromatogr. Sci. 1979, 17, 264. (22) Fushimi, K.; Miyake, Y. J . Geophys. Res. 1980,85,7533. (23) Yokouchi, Y.; Fuggi, T.; Ambe, Y.; Fuwe, K. J. Chromatogr. 1979,180, 133. (24) Grosjean, D. Critical Evaluation and Comparison of Measurement Methods for Nitrogeneous Compounds in the Atmosphere, final report to the Coordinating Research Council, Atlanta, GA. Environmental Research & Technology, Inc., Report no. P-A706, Westlake Viage, CA, 1981. (25) Klippel, W.; Warneck, P. Atmos. Environ. 1980, 14, 809. (26) Lowe, D. C.; Schmidt, U.; Ehhalt, D. H. Geophys. Res. Lett. 1980, 7, 825. Received for review July 20, 1981. Revised manuscript received December 24,1981. Accepted December 24, 1981. Support of this work by the Coordinating Research Council is gratefully acknowledged.
