Aspects of the atmospheric chemistry of amides.

The gas-phase reactions of six amides, formamide, N-methyl formamide, N,N-dimethyl formamide, acetamide, N-methyl acetamide and N,N-dimethyl acetamide with the atmospheric oxidants OH radicals and Cl atoms, but in a number of cases also with NO(3) radicals and ozone, are presented and discussed. Kinetic and mechanistic information available from previous experimental work is combined with new kinetic and product information from this study, obtained in a photoreactor using in situ FTIR spectrometry, to elucidate the gas-phase photooxidation mechanisms of the amides and assess potential environmental implications.

Rate coefficients for the gas-phase reaction of OH radicals with dimethyl sulfide: temperature and O2 partial pressure dependence.

Rate coefficients for the gas-phase reaction of hydroxyl (OH) radicals with dimethyl sulfide (CH(3)SCH(3), DMS) have been determined using a relative rate technique. The experiments were performed under different conditions of temperature (250-299 K) and O(2) partial pressure (approximately 0 Torr O(2)-380 Torr O(2)), at a total pressure of 760 Torr bath gas (N(2) + O(2)), in a 336 l reaction chamber, using long path in situ Fourier transform (FTIR) absorption spectroscopy to monitor the disappearance rates of DMS and the reference compounds (ethene, propene and 2-methylpropene). OH was produced by the photolysis of H(2)O(2). The following Arrhenius expressions adequately describe the rate coefficients as a function of temperature (units are cm(3) molecule(-1) s(-1)): k = (1.56 +/- 0.20) x 10(-12) exp[(369 +/- 27)/T], for approximately 0 Torr O(2); (1.31 +/- 0.08) x 10(-14) exp[(1910 +/- 69)/T], for 155 Torr O(2); (5.18 +/- 0.71) x 10(-14) exp[(1587 +/- 24)/T], for 380 Torr O(2). The results are compared with previous investigations.

Effect of gasoline formulation on the formation of photosmog: a box model study.

Based on exhaust gas analyses from the combustion of five different types of gasoline in a passenger car operated on a chassis dynamometer, box model simulations of the irradiation of exhaust/NOx/air mixtures using an established chemical mechanism for a standardized photosmog scenario were performed. The fuel matrix used covered wide fractional ranges for paraffinic, olefinic, and aromatic hydrocarbons. Two fuels also contained methyl tertiary butyl ether (MTBE). The different O3 profiles calculated for each run were compared and interpreted. The O3 levels obtained were strongly influenced by the exhaust gas concentrations of aromatic and olefinic hydrocarbons. The higher exhaust content of these compounds caused higher O3 production in the smog system investigated. The conclusion of the present study is that the composition of gasoline cannot be taken directly for the estimation of the emissions' O3 creation potential from its combustion. Variation of the dilution in the different calculations showed evidence for an additional influence of transport effects. Accordingly, further detailed exhaust gas analyses followed by more complex modeling studies are necessary for a proper characterization of the relationship between fuel blend and gasoline combustion products.

Formation of methane sulfinic acid in the gas-phase OH-radical initiated oxidation of dimethyl sulfoxide.

Dimethyl sulfoxide (CH3S(O)CH3: DMSO) is an important product of dimethyl sulfide (CH3SCH3: DMS) photooxidation. The mechanism of the OH-radical initiated oxidation of DMSO is still highly uncertain and a major aim of recent studies has been to establish if methane sulfinic acid (CH3S(O)OH: MSIA) is a major reaction product In the present work the products of the OH-radical gas-phase oxidation of dimethyl sulfoxide have been investigated in the absence and presence of NOx All experiments were performed in a 1,080 L reaction chamber in 1,000 mbar synthetic air at 284 +/- 2 K using long-path FT-IR spectroscopy and ion chromatography to monitor and quantify reactants and reaction products. Formation of methane sulfinic acid in high yield (80-99%) was observed in both in the absence and presence of NOx, and the results support that it is the major primary reaction product Other products observed included dimethyl sulfone (CH3S(O)2CH3: DMSO2), sulfur dioxide (SO2), methane sulfonic acid (CH3S(O)2OH: MSA), and methane sulfonyl peroxynitrate (CH3S(O)2OONO2: MSPN). The formation behavior of these products is in line with their source being mainly secondary production via oxidation of a primary product, i.e. MSIA.