Identification of Gas-Phase Dimethyl Sulfate and Monomethyl Hydrogen Sulfate in the Los Angeles Atmospheret Delbert J. Eatough," Vernon F. Whlte, and Lee D. Hansen Thermochemical Institute and Department of Chemistry, Brigham Young University, Provo, Utah 84602
Norman L. Eatough Department of Chemistry, California Polytechnic State University, San Luis Obispo, California 93407
James L. Cheney Environmental Sciences Research Laboratory, Research Triangle Park, North Carolina 277 11
Gas-phase dimethyl sulfate and monomethyl hydrogen sulfate have been identified in the atmosphere in Los Angeles. Gas-phase concentrations of these two alkyl sulfates were determined by using analytical methods based on the collection of the compounds before collection of particles using diffusion denuders and after collection of particles using resin beds or sorption filters, and specific analysis of the collected alkyl sulfates by ion chromatography. The data show that dimethyl sulfate is present in both particles and the gas phase. The concentration of total gas-phase methyl sulfates was found to vary from 34 to 178 nmol/m3 during the smog episode studied. These species constituted a significant fraction of the total sulfur budget in the Los Angeles basin during the sampling period.
Introduction We have previously reported the presence of dimethyl and monomethyl sulfate in coal and oil fly ash and airborne particulate matter (1-4). Durham et al. (5) have collected a gas-phase species with a diffusion coefficient equal to that expected for methylated sulfates by a nylon denuder sampling the atmosphere in Riverside, CA. The species appeared as sulfate in ion chromatographic analysis of samples weeks to months after sample collection. They have also shown that gas-phase monomethyl hydrogen sulfate is collected by nylon denuders and, over time, is converted to sulfate. On the basis of these data they have postulated the presence of gas-phase monomethyl hydrogen sulfate and/or dimethyl sulfate in the Los Angeles basin. If the postulate is correct, their data indicate that the concentrations of gas-phase methylated sulfates are comparable to the concentration of aerosol sulfate in the atmosphere studied. This paper is a report of the results obtained from a 3-day sampling period by using five different simultaneous sampling trains in the Los Angeles basin atmosphere. Details of the validation of the procedures used for the t Contribution
No. 337 from the Thermochemical Institute.
0013-936X/86/0920-0867$0l.50/0
Table I. Configuration of the Sampling System for the Collection of Gas-Phase Alkyl Sulfates sample flow rate, L/min
sampler (1)high vol
DMS, MSA
1000
sampler with quartz filters (2) nylon denuder + quartz filter nylon filter (3) paper denuder + quartz filter + nylon filter (4) quartz filter XAD-I1 bed nylon filter (5) quartz filter + nylon filter + XAD-I1 bed
2.0
DMS, MSA
2.0
DMS, MSA MSA
DMS, MSA
+ + +
material collectedn gas phase particles
DMS, MSA DMS, MSA DMS, MSA
20
DMS MSA DMS, MSA
20
DMS & MSA any DMS passing nylon filter
"DMS is dimethyl sulfate and MSA is monomethyl hydrogen sulfate.
simultaneous collection of both dimethyl sulfate and monomethyl hydrogen sulfate in the gas phase using a variety of diffusion denuders, and filter or resin bed collection systems are reported in another paper (6).
Experimental Section Sampling Techniques. The configurations of the five samplers used for collection of alkyl sulfate compounds are given in Table I. The various procedures have all been tested in the laboratory using samples of gas-phase dimethyl sulfate and monomethyl hydrogen sulfate. Details of the sampling techniques and the verification of the collection of the gas-phase species with the specificity indicated in Table I are given elsewhere (6). Sampler 1 is a high volume cascade impactor with a 15-pm cyclone preseparator. The inlet to the other four samplers contains two impaction plates (PIXE International) with an adhesive surface to remove particles greater in size than 3
0 1986 American Chemical Society
Environ. Sci. Technol., Vol. 20, No. 9, 1986
867
Table 11. Comparison of Results Obtained with Various Techniques for t h e Determination of Gas-Phase Alkyl Sulfate Compounds in the Los Angeles Atmosphere
species (CHs0)zSOz CH30S03H
+
CH30S03H (CH3O)ZSOz
mol of alkyl sulfate/mol of total sulfur for sampling period
sampling system in Table I (3) nylon filter (4) XAD-I1 bed (3) denuderb (3) denuder" (4) nylon filter (2) denuderd (2) Denudere (3) Den + Nylf (3) Den + Nylg (4) XAD-I1 + Nyl (5) Nyl + XAD-I1
1
2
3
4
5
6
7
8
ND" 0.040 0.096 0.096 0.112 0.131 0.112 ND ND 0.152 0.022
ND 0.100 0.229 0.106 0.002 0.137 0.063 ND ND 0.102 0.089
0.056 0.064 0.214 0.190 0.122 0.328 0.129 0.261 0.194 0.186 0.232
0.492 0.397 ND ND 0.035 0.523 0.266 ND ND 0.432 0.270
0.236 0.281 0.394 0.200 0.093 0.603 0.311 0.630 0.436 0.374 0.172
0.350 0.289 ND 0.110 0.093 0.342 0.330 0.460 0.456 0.382 0.440
0.123 0.093 0.295 0.087 0.034 0.218 0.141 0.418 0.210 0.127 0.056
0.124 0.082 ND ND 0.030 0.200 0.135 ND ND 0.112 ND
OND = not determined. bTotal sulfur on paper denuder corrected for SO,; see text. "Monomethyl sulfate only on paper denuder. dTotal sulfur on nylon denuder corrected for SO,; see text. eMonomethyl sulfate only on paper denuder. /Total sulfur on paper denuder corrected for SOz (see text) plus dimethyl sulfate collected on Nylon filter. BMonomethyl sulfate only on paper denuder plus dimethyl sulfate collected on nylon filter. Table 111. Concentration of Various S u l f u r Species Found in t h e Los Angeles Atmosphere
set
date Aug 1 Aug 1 Aug 2 Aug 2 Aug 3 Aug 3 Aug 3 Aug 3
time"
period, h
(CH,0)2S0,b
11:oo
8 10 8 4 4 3 3 4
11 31 33 f 3 164 f 25 80 f 10 89 f 12 62 f 12 50 f 14
20:oo
1o:oo 22:oo 02:oo 07:OO 11:oo
14:OO
concentrations, nmol/m3 gas phase particulate matter CH30SO3HC SOz(g) (CH30)zS0z sulfate 29 f 3 3f6 95 i 37 14 f 20 34 f 29 21 f 11 15 & 11 21 f 21
159 115 252 126 120 80 317 248
0.2
