Daniel Grosjean

Photooxidation of dimethyl sulfide and dimethyl disulfide. I: Mechanism development

Detailed theoretical (Part I, this article) and experimental (Part II) investigations are presented for the mechanism of the atmospheric photooxidation of dimethyl sulfide (CH3SCH3) and dimethyl disulfide (CH3SSCH3). In this paper, comprehensive mechanisms for the atmospheric chemistry of CH3SCH3 and CH3SSCH3 are developed based on fundamental considerations of all available kinetic and mechanistic information.

Formaldehyde and other carbonyls in Los Angeles ambient air

From selective sampling and liquid chromatography analysis, ambient levels of carbonyl compounds as 2,4-dinitrophenylhydrazones have 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 (less than or equal to 35 ppb), propanal (less than or equal to 14 ppb), butanal (less than or equal to 7 ppb), 2-butanone (less than or equal to 14 ppb), and benzaldehyde (less than or equal to 1 ppb). 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.

Parameterization of the formation potential of secondary organic aerosols

Urban particulate matter (PM10) concentrations often include a large contribution from secondary aerosols, i.e. sulfate, nitrate and organic aerosols, which are formed in situ by chemical reactions of their gas phase precursors, SOx, NOx and reactive organic gases (ROG), respectively. For secondary organic aerosols, the results of smog chamber experiments are used to estimate the fraction of ROG that is converted into aerosols, called the fractional aerosol coefficient. An ‘emission parameter’ for secondary organic aerosol can thus be calculated for each ROG. This emission parameter is simply taken as the product of the ROG emission factor and the fractional aerosol coefficient. The secondary organic aerosol emission parameters thus estimated can then be modeled as if secondary organic aerosols formed photochemically in urban air were primary emissions.

Photooxidation of dimethyl sulfide and dimethyl disulfide. II: Mechanism evaluation

The mechanisms for atmospheric photooxidation of CH3SCH3 and CH3SSCH3 developed in Part I are evaluated by a series of outdoor smog chamber experiments. Measured product yields, including SO2, H2SO4, CH3SO3H and HCHO, are reported. The predictions of the mechanisms developed in Part I are found to be in substantial agreement with the measured concentrations from the smog chamber. By comparison of mechanism predictions and observations, critical uncertainties in the mechanism are identified.

Water content of atmospheric aerosols

Abstract The water content of atmospheric aerosol particles is calculated, both above and below the classic deliquescent point. The existence of water in the paniculate phase is predicted to be strongly dependent on the aerosol composition. Liquid water may constitute a significant mass fraction of the aerosol concentration at r.h.

Environmental persistence of organic compounds estimated from structure-reactivity and linear free-energy relationships. Unsaturated aliphatics

Structure-reactivity relationships (SRR) and linear free-energy relationships (LFER) are presented for environmentally important chemical reactions of unsaturated aliphatic contaminants in air and water. SRR of the form log k(k=rate constant for reaction with O3, OH, NO3 NO2 and Cl) vs ionization potential, torsional frequency and absorption maximum, as well as LFER of the form log k (A) vs log k (B), where A and B = O3, OH, NO3, NO2 or Cl are presented and can be used to estimate reaction rate constants and environmental persistence (in air and water) for many unsaturated compounds for which no data exist. As examples of application, rat constants for reactioons with OH (gas phase), OH (water) and NO3 (gas phase) are estimated for some 150 unsaturated compounds including alkenes (from monosubstituted to tetrasubstituted), cycloalkenes, dienes, terpenes, aromatic olefins, unsaturated carbonyls, heterocyclic and other unsaturated organics.

Liquid Chromatography Analysis of Carbonyl (2,4-Dinitrophenyl)hydrazones with Detection by Diode Array Ultraviolet Spectroscopy and by Atmospheric Pressure Negative Chemical Ionization Mass Spectrometry

The (2,4-dinitrophenyl)hydrazones of carbonyls are separated by liquid chromatography and detected by ultraviolet spectroscopy (diode array detector) and by atmospheric pressure negative chemical ionization mass spectrometry. Results are presented for 78 carbonyls including 18 1-alkanals (from formaldehyde to octadecanal), 16 other saturated aliphatic carbonyls (5 C(4)-C(7) aldehydes and 11 C(3)-C(9) ketones), 16 unsaturated aliphatic carbonyls (9 C(3)-C(11) aldehydes and 7 C(4)-C(9) ketones), 13 aromatic carbonyls (including hydroxy- and/or methoxy-substituted compounds), 10 C(2)-C(10) aliphatic dicarbonyls, 3 aliphatic carbonyl esters, and 2 other carbonyls. Isomers were observed for α,β-unsaturated ketones and saturated carbonyls that bear other oxygen-containing substituents, e.g. methoxyacetone, 2-furaldehyde, and the 3 carbonyl esters. For all but two of the carbonyls studied, the base peak in the negative APCI mass spectrum was the M - 1 ion (NO(2))(2)C(6)H(3)NN [Formula: see text] CR(1)R(2) (R(1) = H for aldehydes), where M is the molecular mass of the carbonyl (2,4-dinitrophenyl)hydrazone derivative. The dicarbonyls 2,4-pentanedione and succinic dialdehyde reacted with DNPH to yield predominantly other products. Concentrations measured by ultraviolet spectroscopy (peak area) and by mass spectrometry (abundance of M - 1 ion) were in good agreement. Applications described include the measurement of 34 C(1)-C(18) carbonyls at levels of 0.015-14 parts per billion (ppb) in urban air and the identification of carbonyls at ppb concentrations as reaction products in laboratory studies of the atmospheric oxidation of unsaturated organic compounds.

Gas-particle distribution factors for organic and other pollutants in the Los Angeles atmosphere

The distribution of organic pollutants between the gas and particu-late phases was measured for 6 days Including one with the highest ozone level observed in Pasadena In 1973 (7/25). Gas phase pollutants were monitored continuously while particulates were sampled over a one hour interval by filtration. The filters were extracted using a polar and a non-polar solvent; particulate organic carbon was determined using a carbon analyzer, and chemical analysis carried out by fractionation, gas chromatography, infrared, and CHON analysis. The organic carbon fraction (OCF) was always large, up to 43% of the total particulates (TP). Most of the organics were oxygenated compounds of photochemical origin. There was a linear relation between O3, OCF, and the infrared carbonyl band intensities of the extracts. Hourly variations of OCF and TP are discussed with respect to the gas phase pollutants and conversion processes. Although secondary pollutant concentrations were found in the order: organics > nitrates > sulfate...

Ambient levels of gas phase pollutants in Porto Alegre, Brazil

Abstract Air samples have been collected using electropolished canisters in downtown Porto Alegre, Brazil, where ethanol is used as a vehicle fuel and methyl-tert-butyl ether (MTBE) is used as a vehicle fuel additive. The 150 volatile organic compounds (VOC) identified by GC-FID and GC-MS included 46 alkanes, 30 alkenes, 22 aromatics, 17 carbonyls, 3 alcohols, 8 bicyclic aromatics, 11 halogenated hydrocarbons and 13 other compounds. The most abundant VOC on a mass concentration basis (after CO2, CH4 and CO) included acetylene, MTBE, ethanol, the alkanes propane, n-butane, n-pentane, isopentane, n-hexane, 2-methylpentane and indane, the alkenes ethylene and propene, and the aromatics benzene, toluene, ethylbenzene and (m+p) xylene. During the ca. one-year period studied, 20 March, 1996–16 April, 1997, ambient concentrations of VOC correlated well with those of carbon monoxide, for which vehicle exhaust emissions account for ca. 99% of total emissions in Porto Alegre. Two VOC photochemical reactivity rankings are presented: one involves reaction with OH (product of VOC concentration and VOC–OH reaction rate constant) and the other involves production of ozone (product of VOC concentration and VOC maximum incremental reactivity coefficient). Reaction with OH is dominated by CO followed by 2-methyl-2-butene and by several other alkenes. Ozone production is dominated by ethylene and CO (about equal contribution) followed by several alkenes, alkylbenzenes and aldehydes. The two fuel oxygenates, ethanol and MTBE, play only a minor role as photochemical precursors (reaction with OH and production of ozone) in the atmosphere of Porto Alegre.

Carbonyls in urban fog, ice fog, cloudwater and rainwater

Formaldehyde, acetaldehyde, propanal, acetone + acrolein, n-butanal, 2-butanone, n-pentanal, n-hexanal and benzaldehyde have been identified in fog, ice fog, mist, cloudwater and rainwater samples collected at urban locations in California (Los Angeles) and Alaska (Fairbanks). Formaldehyde concentrations, up to ~ 2 mg l−1, were highest in urban fog and ice fog samples. Concentrations of other carbonyls occasionally approached or exceeded that of formaldehyde. The results are briefly discussed in terms of scavenging of gas-phase atmospheric carbonyls.