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.

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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

The absolute rate constants for the reactions of NH2 radicals with ethyl, isopropyl, and t-butyl radicals have been measured at 298 K, using a flash photolysis–laser resonance absorption method. Radicals were generated by flashing ammonia in the presence of an olefin. A new measurement of the NH2 extinction coefficient and oscillator strength at 597.73 nm was performed. The decay curves were simulated by adjusting the rate constants of both the reaction of NH2 with the alkyl radical and the mutual interactions of alkyl radicals. The results are k(NH2 + alkyl) = 2.5 (±0.5), 2.0 (±0.4), and 2.5 (±0.5) × 1010M−1·s−1 for ethyl, isopropyl, and t-butyl radicals, respectively. The best simulations were obtained when taking k(alkyl + alkyl) = 1.2, 0.6, and 0.65 × 1010M−1·s−1 for ethyl, isopropyl, and t-butyl radicals, respectively, in good agreement with literature values.

Absolute rate constants for the reactions between amino and alkyl radicals at 298 K

Rate constant for the reaction of nh2 with ozone in relation to atmospheric processes

Rate constant for the reaction of the CFCl2 radical with oxygen in the pressure range 0.2–12 Torr at 298 K

Kinetics of the Association Reactions of NO with the Series of Chlorofluoromethyl Radicals CFxCl3-x

The rate constant for the combination reaction of CFCl2O2 and NO2 was measured as a function of pressure and temperature under stratospheric conditions. The results show that the reaction is fast and that significant amounts of the peroxynitrate CFCl2O2NO2 can be formed. The data were introduced into a 2D photochemical model in order to evaluate an upper limit for the amount of chlorine stored in the form of the peroxynitrate. The calculation shows that this reservoir effect cannot exceed a few percent of the total chlorine contained in the stratosphere.

Robert Lesclaux

Papers

Absolute rate constants for the reactions between amino and alkyl radicals at 298 K

Rate constant for the reaction of nh2 with ozone in relation to atmospheric processes

Rate constant for the reaction of the CFCl2 radical with oxygen in the pressure range 0.2–12 Torr at 298 K

Kinetics of the Association Reactions of NO with the Series of Chlorofluoromethyl Radicals CFxCl3-x

The rate of formation of halomethyl peroxy nitrates in the stratosphere and their possible role as temporary reservoirs for ClOx and NOx species