Atmospheric degradation of volatile organic compounds

A model for the photochemistry of the global troposphere constrained by observed concentrations of H2O, O3, CO, CH4, NO, NO2, and HNO3 is presented. Data for NO and NO2 are insufficient to define the global distribution of these gases but are nonetheless useful in limiting several of the more uncertain parameters of the model. Concentrations of OH, HO2, H2O2, NO, NO2, NO3, N2O5, HNO2, HO2NO2, CH3O2, CH3OOH, CH2O, and CH3CCl3 are calculated as functions of altitude, latitude, and season. Results imply that the source for nitrogen oxides in the remote troposphere is geographically dispersed and surprisingly small, less than 107 tons N yr−1. Global sources for CO and CH4 are 1.5 × 109 tons C yr−1 and 4.5 × 108 tons C yr−1, respectively. Carbon monoxide is derived from combustion of fossil fuel (15%) and oxidation of atmospheric CH4 (25%), with the balance from burning of vegetation and oxidation of biospheric hydrocarbons. Production of CO in the northern hemisphere exceeds that in the southern hemisphere by about a factor of 2. Industrial and agricultural activities provide approximately half the global source of CO. Oxidation of CO and CH4 provides sources of tropospheric O3 similar in magnitude to loss by in situ photochemistry. Observations of CH3CCl3 could offer an important check of the tropospheric model and results shown here suggest that computed concentrations of OH should be reliable within a factor of 2. A more definitive test requires better definition of release rates for CH3CCl3 and improved measurements for its distribution in the atmosphere.

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Tropospheric chemistry: A global perspective

This overview compiles the actual knowledge of the biogenic emissions of some volatile organic compounds (VOCs), i.e., isoprene, terpenes, alkanes, alkenes, alcohols, esters, carbonyls, and acids. We discuss VOC biosynthesis, emission inventories, relations between emission and plant physiology as well as temperature and radiation, and ecophysiological functions. For isoprene and monoterpenes, an extended summary of standard emission factors, with data related to the plant genus and species, is included. The data compilation shows that we have quite a substantial knowledge of the emission of isoprene and monoterpenes, including emission rates, emission regulation, and biosynthesis. The situation is worse in the case of numerous other compounds (other VOCs or OVOCs) being emitted by the biosphere. This is reflected in the insufficient knowledge of emission rates and biological functions. Except for the terpenoids, only a limited number of studies of OVOCs are available; data are summarized for alkanes, alkenes, carbonyls, alcohols, acids, and esters. In addition to closing these gaps of knowledge, one of the major objectives for future VOC research is improving our knowledge of the fate of organic carbon in the atmosphere, ending up in oxidation products and/or as aerosol particles.

Biogenic Volatile Organic Compounds (VOC): An Overview on Emission, Physiology and Ecology

. The last decade has seen tremendous advances in atmospheric aerosol particle research that is often performed in the context of climate and global change science. Biomass burning, one of the largest sources of accumulation mode particles globally, has been closely studied for its radiative, geochemical, and dynamic impacts. These studies have taken many forms including laboratory burns, in situ experiments, remote sensing, and modeling. While the differing perspectives of these studies have ultimately improved our qualitative understanding of biomass-burning issues, the varied nature of the work make inter-comparisons and resolutions of some specific issues difficult. In short, the literature base has become a milieu of small pieces of the biomass-burning puzzle. This manuscript, the second part of four, examines the properties of biomass-burning particle emissions. Here we review and discuss the literature concerning the measurement of smoke particle size, chemistry, thermodynamic properties, and emission factors. Where appropriate, critiques of measurement techniques are presented. We show that very large differences in measured particle properties have appeared in the literature, in particular with regards to particle carbon budgets. We investigate emissions uncertainties using scale analyses, which shows that while emission factors for grass and brush are relatively well known, very large uncertainties still exist in emission factors of boreal, temperate and some tropical forests. Based on an uncertainty analysis of the community data set of biomass burning measurements, we present simplified models for particle size and emission factors. We close this review paper with a discussion of the community experimental data, point to lapses in the data set, and prioritize future research topics.

/pdf/a-review-of-biomass-burning-emissions-part-iii-intensive-4onlsstr3d.pdf

A review of biomass burning emissions part III: intensive optical properties of biomass burning particles

https://www.engr.colostate.edu/~marchese/combustion10/3.pdf

A Comprehensive Modeling Study of iso-Octane Oxidation

Flash photolysis coupled to UV absorption spectrometry was used for a relative measurement of
 the (CH3)2CHCO and (CH3)3CCO radical decomposition rate constants. The reference reaction was the association
 reaction of (CH3)2CHCO and (CH3)3CCO with O2, for which the same rate constant as that
 of the CH3CO+O2 reaction was assumed: k2=3.2×10−12 cm3
 molecule−1 s−1 (R. Atkinson, D. L. Baulch, R.A. Cox,
 R. F. Jr. Hampson, J. A. Kerr, M. J. Rossi and J. Troe, J. Phys. Chem. Ref. Data, 1999, 28, 191), independent of temperature. The rate expressions obtained at atmospheric pressure (N2+O2)
 for decomposition are k[(CH3)2CHCO]=3.8×10(12±1) exp[−(5970±600) K/T] s−1 (413 K<T<503
 K) and k[(CH3)3CCO]=1.65×10(12±1) exp[−(4870±310) K/T] s−1 (323 K<T<453 K). RRKM calculations were also
 performed in order to assess the pressure dependence of rate constants. The reactions are in the fall-off region
 at atmospheric pressure and in the temperature range investigated. Calculations were fitted to experimental data and have yielded at the high pressure limit k∞[(CH3)2CHCO)=3.3×1014 exp(−7145 K/T) s−1 and k∞[(CH3)3CCO]=1.1×1014 exp(−6090 K/T) s−1, in fairly good agreement with the expressions derived
 from transition state theory calculations. The detailed results are given in the form of the Troe expression.
 The atmospheric implications of the results are discussed. In particular, the results suggest that the class
 of RCO radicals containing only alkyl R groups cannot
 decompose
 in the troposphere
 and thus, add to O2 to form acylperoxy radicals RC(O)O2.

Robert Lesclaux

Papers

Kinetics of the (CH3)2CHCO and (CH3)3CCO radical decomposition: temperature and pressure dependences

The kinetics of the gas phase reactions of NH2 radicals with alkane and alkyl radicals

The kinetics of the reaction between NH2 and propylene studied by laser resonance absorption

Self-reaction kinetics of the (CH3)2CHC(O)O2 and (CH3)3CC(O)O2 acylperoxy radicals between 275 and 363 K

Kinetic and Mechanistic Studies of the Reactions of Cyclopentylperoxy and Cyclohexylperoxy Radicals with HO2.