Peroxypropionyl Nitrate at a Southern California Mountain Forest Site Edwln L. Williams, I 1 and Daniel Grosjean” DGA, Inc., 4526 Telephone Road, Suite 205, Ventura, California 93003
Ambient levels of peroxyacetyl nitrate (PAN) and peroxypropionyl nitrate (PPN) have been measured at one mountain forest site (Tanbark Flat, elevation 800 m in southern California’s San Gabriel Mountains), during the period August 8-October 16, 1989. Peroxy-n-butyryl nitrate (PnBN) was tentatively identified from a combination of laboratory experiments and field observations. Average concentrations during the study period were 2.9 ppb for PAN, 0.75 ppb for PPN, and 0.05 ppb for PnBN. Highest concentrations measured were >16 ppb for PAN, 5.1 ppb for PPN, and 0.6 ppb for PnBN. Diurnal and seasonal variations are discussed in terms of “horizontal” transport of polluted air to the mountains, “vertical” transport reflecting inversion strength and mixing height, and a possible contribution of biogenic hydrocarbons. PPN/PAN concentration ratios calculated from some 3000 paired measurements were linearly correlated, i.e., PPN/PAN = 0.280 f 0.001 (intercept = -0.073 f 0.002, R = 0.943). The PPN/PAN ratios are discussed in terms of formation and removal processes for PAN and PPN. Since PPN is 2-8 times more phytotoxic than PAN, P P N must be included in any realistic assessment of forest and crop damage by photochemical oxidants. Introduction Gaseous pollutants that may adversely impact vegetation include ozone, peroxyacetyl nitrate (PAN, CH3C(O)OONO,), and higher peroxyacyl nitrates, RC(0)OONO,. The adverse effects of ozone on forests and crops are well documented, and some information is available for PAN as well (1-3). However, much less information is available regarding the phytotoxicity of the higher peroxyacyl nitrates, and there are virtually no data regarding their ambient concentrations. Higher homologues of PAN, including peroxypropionyl nitrate (PPN, CH3CHzC(0)OON0,),peroxy-n-butyryl nitrate (PnBN, CH3CH,CHzC(0)OON0,), and peroxyisobutyryl nitrate (PiBN, (CH3),CHC(0)OON02)may be more phytotoxic than PAN (1). By use of electron capture gas chromatography (EC-GC), P P N has been observed in a limited number of urban settings ( 4 , 5 ) . Approximate levels have been reported, assuming that the EC-GC response to PPN is identical with that for PAN. Ambient levels of higher peroxyacyl nitrates, including PnBN and PiBN, have not been measured. In addition to the phytotoxic properties, peroxyacyl nitrates are eye irritants (6)possible agents of skin cancer (7), and mutagens (8, 9). Peroxyacyl nitrates have no known direct sources and are therefore excellent indicators of photochemical pollution (10). They serve as vehicles (“reservoirs”) for the long-range transport of reactive ni0013-936X/91/0925-0653$02.50/0
trogen over regional and continental scales (11-15). In this article, we present quantitative measurements of PPN in ambient air. These measurements were carried out at a southern California mountain forest location, the San Dimas Experimental Forest a t Tanbark Flat in the San Gabriel Mountains (elevation 800 m, 35 km northeast of Los Angeles). Air quality and vegetation damage at this location have been extensively characterized (16,17). PAN was also measured in order to obtain information regarding the relative concentrations of the first two, and most abundant, peroxyacyl nitrates. Qualitative information is also presented regarding the higher homologue peroxy-nbutyryl nitrate. Experimental Methods Gas Chromatography Measurements. PAN, PPN, and PnBN were measured on site by electron capture gas chromatography (6,18-22) using an SRI Model 8610 GC and a Valco Model 140 BN EC detector. The column used was a 70 cm X 3 mm Teflon-lined stainless steel column packed with 10% Carbowax 400 on Chromosorb P, acid washed, and treated with dimethyldichlorosilane. The column and detector temperatures were 36 and 60 “C, respectively. The carrier gas was ultrahigh-purity nitrogen. The column flow rate was 58 mL/min. Ambient air was continuously pumped through a 25-mm-diameter, 1.2-pm pore size Teflon filter, a 6.4 m X 6 mm Teflon sampling line, and a 6.7-mL stainless steel loop housed in the GC oven. The residence time in the sampling line was 21 s. Ambient air was injected every 30 min with a timer-activated 10-port sampling valve. Typical PAN and P P N retention times were 3.1 and 3.8 min, respectively. The retention time of the peak we tentatively identified as PnBN was 6.4 min. The detection limits were 0.01,0.02, and 0.02 ppb for PAN, PPN, and PnBN, respectively. Interference Studies. Chlorinated hydrocarbons are detected by EC-GC and may therefore interfere in the determination of peroxyacyl nitrates. The halogenated hydrocarbons CH2C1,, CHCl,, CCl,, CH3CC13,CZCl4,CC1,F (Freon l l ) , and CClzFz (Freon 12) have been detected by EC-GC under the conditions used for PAN analysis on capillary columns (23). Carbon tetrachloride, methyl chloroform, and tetrachloroethylene have been detected by using EC-GC under the conditions used for PAN analysis on a column packed with the same phase as the one used in this study (20, 24). A standard mixture obtained from Dr. Rei Rasmussen and calibrated in his laboratory was reanalyzed in our laboratory under conditions identical with those we employed for the field measurements. The mixture contained 18 compounds including chlorinated, brominated, and aromatic hydro-
0 1991 American Chemical Society
Environ. Sci. Technol., Vol. 25, No. 4, 1991 653
Table I. Composition of Standard Mixture
compound 1,3-butadiene benzene toluene chlorobenzene ethylbenzene o-xylene vinyl chloride methyl bromide F11 (CFCln)
nominal concn PPb 1.08 0.93 0.53 0.55 0.52 0.55 1.02 0.5 0.53
compound methylene chloride chloroform 1,2-dichloroethane methylchloroform carbon tetrachloride 1,2-dichloropropane trichloroethylene 1,2-dibromoethane tetrachloroethylene
nominal concn PPb
Environ. Sci. Technol., Vol. 25, No. 4, 1991
I
1.09
1.07 1
0.52 1
0.54 1.09 0.55 1.06
carbons, each a t concentrations of 0.5-1.1 ppb (Table I). With the exception of C2C14,which eluted with a retention time of 1.33 min, none of the compounds listed in Table I was observed in chromatograms of up to 12 min. Thus, these compounds (a) coelute early with the large oxygen peak, (b) are retained on the column and/or elute after more than 12 min, or (c) are not detected a t levels of 0.5-1.1 ppb under the conditions we used to measure PAN and P P N in ambient air. Calibrations and Structure Assignment. To calibrate our EC-GC instrument, we prepared pure PAN and P P N in n-dodecane by nitration of peracetic acid and perpropionic acid, respectively (25,26). Parts per billion levels of PAN and P P N in the gas phase were obtained by passing purified air over the PAN/dodecane or PPN/dodecane mixture contained in an impinger. We also used another method to prepare ppb levels of PAN, PPN, PnBN, and PiBN in order to confirm their identity and retention times. This method involved sunlight irradiation, in a 3.5-m3 Teflon chamber, of 0.2 ppm nitric oxide and 1 ppm of an olefin or aldehyde in purified air. PAN was prepared from acetaldehyde or from 2-methyl-2-butene (27),PPN was prepared from propanal, mixtures of PAN and PPN were prepared from trans-2-pentene, and PnBN was prepared from n-butanal. Most of the ambient air chromatograms recorded a t Tanbark Flat contained five peaks eluting in the following order: oxygen, tetrachloroethylene, PAN, PPN, and a compound that eluted at 5.9 f 0.27 min. This compound is most likely a chlorinated hydrocarbon, Freon, alkyl nitrate, or peroxyacyl nitrate since the electron capture detector is highly selective to these compounds. Of these, only peroxyacyl nitrates are thermally unstable (28) and decompose a t T > 100 "C. Indeed, when ambient air was passed through a Teflon tube heated to 157 "C and then injected into the EC-GC, the peak corresponding to the unknown compound disappeared, along with those of PAN and PPN. Thus, the unknown compound is most likely a peroxyacyl nitrate, with PnBN and PiBN being the two most likely candidates. An attempt to prepare PiBN in situ yielded inconclusive results: irradiation of a mixture of nitric oxide and isobutanal in a Teflon chamber produced 0.8 ppb of PAN as well as another compound ( t R = 1.4 min), which did not decompose a t 150 "C. The compound eluting at 1.4 min is probably an alkyl nitrate, and PAN is a possible reaction byproduct. If PiBN was produced, it was not observed under the conditions employed. In situ preparation of PnBN was successful: irradiation of 0.25 ppm nitric oxide and 1 ppm n-butanal resulted in the formation of a compound that eluted at 5.6 f 0.1 min and thermally decomposed a t 150 "C. The GC retention time ratios tR(PnBN)/tR(PAN)from the laboratory experiment, 1.923 f 0.003, agreed within 2 standard deviations with that measured in the field for the unknown compound, 2.05 f 0.24. Thus, the unknown compound 654
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2
20
-
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I
400
800
1200
1600
"
" 2000
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I
2400
2800
3200
PAN Peak Height (At13), rnm
Figure 1. EC-GC calibration for PAN.
observed in the field is most likely PnBN, although we cannot rule out its isomer PiBN, or a mixture of the two isomers. Calibrations were carried out by dilution of an initial 60-80 ppb concentration of PAN and PPN in purified air contained in a 1-m3Teflon-lined chamber. Purified dilution air was added to the chamber a t a flow rate of 1 L/min. PAN or P P N were measured every 30 min by EC-GC, and the corresponding NO, concentration was monitored continuously with a calibrated chemiluminescence NO, analyzer (Monitor Labs 8840). The NO, value from the chemiluminescence analyzer was used to quantitate the PAN and P P N peak height from the GC chromatogram, since chemiluminescence analyzers respond quantitatively to PAN and P P N (29). Peak height vs concentration plots were constructed and are shown in Figures 1 and 2. These plots were nonlinear a t concentrations above 26 and 16 ppb, respectively. Plots of peak height or NO, analyzer response vs l/dilution for PAN and P P N show that both the NO, analyzer and the EC-GC responded nonlinearly at high concentrations of PAN and PPN. Regression analysis of the experimental data (least squares, forced through zero, PAN < 26 ppb and PPN C16 ppb) yielded the following slopes, i.e., calibration factors: PAN: 0.01189 + 0.00017 ppb/mm R = 0.9876 PPN: 0.01522
+ 0.00030 ppb/mm
R = 0.9931
Thus, the EC-GC response to P P N is 28% less than its response to PAN under our experimental conditions. This may reflect a lower response of the EC detector to PPN, greater losses of P P N in our EC-GC system, or both. No attempt was made to calibrate the EC-GC for PnBN. PnBN concentrations were calculated by assuming that the EC-GC response to PnBN is the same as that to PPN. Results and Discussion PAN, P P N , and PnBN were measured every 30 rnin from August 8 to October 16, 1989,thus yielding some 3000 observations for each compound. Individual values have
5.4 - 6.0
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.~.
8/10 8/11 8/12 8/13 8ji4 8/15 8/16 8/17 8/16 8/19 8/20 8/21 8/22 8/23 8/24 8/25 ai26 8/27 8/28 8/29 8/30 8/31 911 9j2 913 914 915 916 917 918 919 9/10 9/11
PAN, ppb lowest highest 0.48 0.11 0.54
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0
6.66
0.55 0.62 0.86 0.76 0.52 ND 1.33 0.88 0 1.74 2.47 1.9 1.81 1.9 1.68 3.02 1.95 0.88 0.08 0.58 0.05
2.35 2.66 1.9 2.24 2.43 ND 1.57 5.23 4.61 5.02 5.56 4.99 7.61 4.09 6.33 3.42 5.33 >7.1 7.47 4.71 6.85
0.02
7.06
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average
PPN, ppb lowest highest
0.22 0.28 0.38 0.31 0.3
0.29 0.34 0.46 0.33 ND (a) 0.18 (a) 0.95 0.89 0.19 1.03 0.97 0.99 0.84 1.16 0.29' 1.05' 0.76 0.63 0.79 0.93 0.89 0.83 0.68
0.7 0.81 0.54 1.01 1.86 1.85 1.51
0.09 0.14 0.13 0.1 0.14 0.12 0.18 0.15 0.09 ND 0.24 0.24 0.5 0.38 0.67
0.38 0.64 0.68 0.89 0.84 0.82 0.65 0.76
0.79 ND 0.3 1.86 1.53 1.67 1.95 1.82 1.83 1.37 2.25 0.88 1.89 2.92 1.92 1.6 2.53 2.47 1.9 2.25 2.5 1.58 1.35 2.22 2.34 2.62 1.89
0.5 0.5
0.55 0.46 0
0.52 0.03 0 0.12 0 0 0.03 0.04 0.03 0.24 0.02 0.18 1.34 1.03
0.24
date 9/12 9/13 9/14 9/15 9/16 9/17 9/18 9/19 9/20 9/21 9/22 9/23 9/24 9/25 9/26 9/27 9/28 9/29 9/30 1011 1012 1013 1014 1015
1016 10/7
1018 1019 lOjl0 lO/ll
10/12 10113 10114 10115 10116
PAN. ppb average lowest highest >5.4 2.44 >1.59 3.71 2.81 0.95 0.66 1.51 3.3 1.63 2.77 3.11 1.54 1.37 2.75 2.92 1.67 2.43 1.97 2.83 1.63 1.96 2.89 2.22 2.93 2.92 3.16 2.87 >6.2ZC >a201 X.59 >6.83 7.99 8.16 4.75
3.19 0.32 0.13 0.6 0.87 0
0.12 0.34 1.52 0.14 0.14 0.29 0.05 0.05 0.05
0.52 0.1 0.48 0.29 1.05 0.67 0.19 0.57 0.48 1.43 0.29 0.38 0.38 1.33 2.66 1.14 0.67
2.09 3.14 0.05
>7.1 6.63 >7.1 9.23 11.65 4.42 2.14 3.09 6.66
4.95 10.37 11.7 5.23 5.04 13.22 6.66 9.61 6.94 6.56 7.99 2.76 4.19 5.8 6.37 8.85 6.85 14.17 10.27 >13.5 >12.4 >15.0 >14.8 14.17 16.08 11.226
average 1.75 0.65
0.39 1.1 0.73
PPN, ppb lowest highest 0.94 0.02 0 0 0.08
0.14 0.09 0.34 0.9 0.37 0.78
0 0 0.02 0.41
0.16
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0.38 0.31 0.74 0.83 0.39 0.58 0.43 0.66 0.3
0.38 0.54 0.4 0.65 0.6 0.65 0.6 1.4ff 1.69' 1.85 1.67 1.77 1.62 1.03
0 0
0
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0.02 0
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0 0 0
2.68 2.1 2.44 2.92 1.83 0.97 0.53 0.84 1.83 1.29 3.29 3.41 1.54 1.83 3.9 2.07 2.8 1.83 1.58 1.74 0.58 0.88 1.54 1.45 2.07 1.55 3.65 2.56 4.02 3.65 4.75 4.63 5.11 3.9 2.31d
'No data from 8/16,22:30 h to 8/18, 2k30 h. 'No data from 8/27, 1 2 5 h to 8/28, 1225 h. CNodata from 10/10, 1818 h to lO/ll, 6:48 h. dNo data after 11:18 h.
0.45
- 0.50
0.40. 0.45
3
0.25
pounds (36, 37). Variations in hydrocarbon precursor concentrations (e.g., propene for PAN, 1-butene for PPN, 2-pentene for both, etc.), along with the relative reactivities of these hydrocarbons toward OH, ozone, and NO8, will influence the PPN/PAN ratio in a manner directly related to fuel composition and to transport time from hydrocarbon emission sources to the receptor site, i.e., Tanbark Flat. PPN is expected to react faster with OH than PAN does, thus resulting in a more rapid removal during transport. A more detailed examination of these parameters would require the compilation of meteorological, emission, and air quality data and was beyond the scope of this study. We note, however, that the overall PPN/ PAN ratio data base could be divided into two subsets. The first subset (August 8-September 23) yielded a linear regression fit with a slope of 0.310 f 0.002, R = 0.965. The second subset (September 23-October 16) also yielded a good linear fit but with a lower PPN/PAN ratio, 0.230 i 0.002, R = 0.930. The lower ratio observed during the last part of the study may reflect changes in transport time, changes in emission patterns of PAN and PPN precursors (anthropogenic and biogenic), or both.
Y
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200
,
,
,
,
,
400
600
800
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1200
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Acknowledgments ?E
Number 01 Observations
Wn 11.
Frequency disbbutii of Um PPNIPAN mnceniratkm ratios.
the OH radical. PAN and P P N have similar thermal stabilities, with k = 4.9 X lo4 s-l at 298 K for both com658
Environ. Sci. Technol., VoI. 25. No. 4. 1991
We thank Dr. John Palmer and Dr. Robert Farber (Southern California Edison Co.) for technical advice throughout this project. Dr. Andrzej Bytnerowin and Mr. Phil Dawson (U. of California, Riverside) provided critically important field support and participated in interlaboratory comparison studies. Dr. Rei Rasmussen (Ore-
gon Graduate Center) kindly provided a standard mixture of hydrocarbons prepared and calibrated in his laboratory. Mr. Eric Grosjean assisted in field operations, Mr. Fabrice ~~~~j~~~assisted in data reduction, M ~ ~i~~ . ~ ~ assisted in computer data processing? and MS. Denise Yanez prepared the draft and final versions of this report. Literature Cited Tavlor. 0. C. J . Air Pollut. Control Assoc. 1969.19.347-351. TaGlor', 0. C.; MacLean, D. C. Nitrogen oxides and the peroxyacyl nitrates. In Recognition of Air Pollution Injury to Vegetation: A Pictorial Atlas; Jacobson, J. S., 'Hill, A. C., Air Pollution Control Association: Pittsburgh, PA, 1970; pp El-El4. Mudd, J. B. Peroxyacyl nitrates. In Responses of Plants t o Air Pollution; Mudd, J. B. Kozlowski, T. T., Eds.; Academic Press: New York, 1975; pp 97-119. Altshuller, A. P. Atmos. Enuiron. 1983, 17, 2383-2427. Roberts, J. M. Atmos. Enuiron. 1990, 24A, 243-287. Stephens, E. R. Adu. Enuiron. Sci. Technol. 1969, I, 119-146. Lovelock, J. E. Ambio 1977, 6, 131-133. Peak, M. J.; Belser, W. L. Atmos. Enuiron. 1969,3,385-397. Kleindienst, T. E.; Shepson, P. B.; Edney, E. 0.;Claxton, L. D. Mutat. Res. 1985, 157, 123-128. Nielsen, T.; Samuelsson, U.; Grennfelt, P.; Thompson, E. Nature 1981,293, 553-555. Singh, H. B.; Hanst, P. L. Geophys. Res. Lett. 1981, 8, 941-944. Singh, H. B.; Salas, L. J.; Ridley, B. A.; Shetter, J. D.; Donohue, N. M.; Fehsenfeld, F. C.; Fahey, D. W.; Parrish, D. D.; Williams, E. J.; Liu, S. C.; Huebler, G.; Murphy, P. C. Nature 1985,318, 347-349. Fahey, D. W.; Huebler, G.; Parrish, D. D.; Williams, E. J.; Norton, R. B.; Ridley, B. A,; Singh, H. B.; Liu, S. C.; Fehsenfeld, F. C. J . Geophys. Res. 1986, 91, 9781-9793. Kasting, J. F.; Singh, H. B. J . Geophys. Res. 1986, 91, 13239-13256. Singh, H. B. Enuiron. Sci. Technol. 1987, 21, 320-327. Miller, P. R.; Taylor, 0. C.; Poe, M. P. Spatial variation of summer ozone concentrations in the San Bernardino mountains. Presented at the 79th annual meeting of the Air Pollution Control Association, Minneapolis, MN, June 22-27, 1986. Bytnerowicz, A.; Miller, P. R.; Olszyk, D. M.; Dawson, P. J.; Fox, C. A. Atmos. Enuiron. 1987, 21, 1749-1849. Williams, E. L., II; Grosjean, D. Atmos. Enuiron. 1990,24A, 2369-2377. Williams, E. L., II; Grosjean, D. Impact of Los Angeles smog on air quality in the San Gabriel Mountains Forest: Ambient levels of peroxyacetyl nitrate (PAN), peroxypropionyl nitrate (PPN), formaldehyde and acetaldehyde at Tanbark Flat. Final report to the Southern California Edison Co., DGA, Inc. Ventura, CA April 1990. Hisham, M. W. M.; Grosjean, D. Air pollution in southern California museums: nitrogen dioxide, peroxyacetyl nitrate,
(21) ~ (22) (23) (24)
(25) (26) (27) (28) (29) (30) (31) (32)
(33)
(34) (35) (36)
(37)
nitric acid, and chlorinated hydrocarbons. Final report to the Getty Conservation Institute, DGA, Inc., Ventura, CA, 1989. Sin&, ~ H. B.; l Salas,l L. J. ~Atmos. Enuiron. 1989, 23, 1, 231-238. Tanner,R, L.; Miguel, A. H.; de Andrade, J. B.; Gaffney, J. S.: Streit. G. E. Enuiron. Sci. Technol. 1988, 22, 1026-1034. ' Roberts, J. M.; Fajer, R. W.; Springston, S. R. Anal. Chem. 1989 67. _"__ _,_771-772 .,. - . Hisham, M. W. M.; Grosjean, D. Southern California Air Quality Study: toxic air contaminants, Task 1. Final Report to California Air Resources Board, Agreement A832-152, DGA, Inc., Ventura, CA, 1990. Nielsen, T.; Hansen, A. M.; Thomsen, E. L. Atmos. Enuiron. 1982, 16, 2447-2450. Gaffney, J. S.;Fajer, R.; Senum, G. I. Atmos. Environ. 1984, 18, 215-218. Grosjean, D. Enuiron. Sei. Technol. 1990, 24, 1428-1432. Cox, R. A.; Roffey, M. J. Enuiron. Sci. Technol. 1977, 11, 901-906. Grosjean, D.; Harrison, J. Environ. Sei. Technol. 1985,19, 862-865. Temple, P. J.; Taylor, 0. C. Atmos. Enuiron. 1983, 17, 1583-1587. Grosjean, D. Atmos. Enuiron. 1984, 18, 7, 1489-1496. Hisham, M. W. M.; Grosjean, D. Air pollution in Southern California Museums: sulfur dioxide, total reduced sulfur, chlorinated hydrocarbons and photochemical oxidants. Final report to the Getty Conservation Institute, DGA, Inc., Ventura, CA, 1990. Ciccioli, P.; Brancaleoni, E.; DiPalo, C.; Brachetti, A.; Cecinato, A. Daily trends of photochemical oxidants and their precursors in a suburban forested area. A useful approach for evaluating the relative contributions of natural and anthropogenic hydrocarbons to the photochemical smog formation in rural areas in Italy. Proceedings of the Fourth European Symposium on Physio-Chemical Behavior of Atmospheric Pollutants, Stresa, Italy, September 23-25, 1986. Ciccioli,P.; Brancaleoni, E.; Di Palo, V.; Liberti, V.; DiPalo, C. Misura delle alterazoni della qualita dell'aria da fenomeni di smog fotochimico. Acqua Aria 1986, 7, 675-683. Lonneman, W. A.; Bufalini, J. J.;Seila, R. L. Enuiron. Sci. Technol. 1976,10, 374-380. Schurath, U.; Wipprecht, V. Reactions of peroxyacyl radicals. Proceedings of the first European symposium on physio-chemical behavior of atmospheric pollutants, Ispra, Italy, Versino, B., Ott, H., Eds. Commission of the European communities, 1979. Atkinson, R. Atmos. Enuiron. 1990, 24A, 1-41.
Received for review June 1, 1990. Revised manuscript received October 10, 1990. Accepted November 1, 1990. This work has been sponsored by the Southern California Edison Co., Rosemead, CA.
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