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.

/pdf/tropospheric-chemistry-a-global-perspective-29u7u1il4s.pdf

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

Global atmospheric models play a key role in international assessments of the human impact on global climate and air pollution. To increase the accuracy and facilitate comparison of results from such models, it is essential they contain up-to-date chemical mechanisms. To this end, we present an evaluation of the atmospheric chemistry of the four most abundant organic peroxy radicals: CH3O2, C2H5O2, CH3C(O)O2, and CH3C(O)CH2O2. The literature data for the atmospheric reactions of these radicals are evaluated. In addition, the ultraviolet absorption cross sections for the above radicals and for HO2 have been evaluated. The absorption spectra were fitted to an analytical formula, which enabled published spectra to be screened objectively. Published kinetic and product data were reinterpreted, or in some case reanalyzed, using the new cross sections, leading to a self-consistent set of kinetic, mechanistic, and spectroscopic data. Product studies were also evaluated. A set of peroxy radical reaction rate coefficients and products are recommended for use in atmospheric modeling. A three-dimensional global chemical transport model (the Intermediate Model for the Global Evolution of Species, IMAGES) was run using both previously recommended rate coefficients and the current set to highlight the sensitivity of key atmospheric trace species to the peroxy radical chemistry used in the model.

https://agupubs.onlinelibrary.wiley.com/doi/epdf/10.1029/2000JD900746

Atmospheric chemistry of small organic peroxy radicals

The laser flash photolysis/UV absorption spectrometry technique has been used to investigate the kinetics of the peroxy radical permutation reactions (i.e. self and cross reactions) arising from the OH-initiated oxidation of isoprene (2-methyl-1,3-butadiene), and of the simpler, but related conjugated dienes, 1,3-butadiene and 2,3-dimethyl-1,3-butadiene. The results of the two simpler systems are analysed to provide values of the rate coefficients for the 6 peroxy radical permutation reactions of the three types of isomeric peroxy radical produced in each system (T = 298 K, P = 760 Torr). The rate coefficients are all significantly larger than values estimated previously by extrapolation of structure-reactivity relationships based on the kinetics of a limited dataset of simpler radicals containing similar structural features. The results are discussed in terms of trends in self and cross reaction reactivity of primary, secondary and tertiary peroxy radicals containing combinations of allyl, β-hydroxy and δ-hydroxy functionalities. Since the peroxy radicals formed in these systems are structurally very similar to those formed in the isoprene system, the kinetic parameters derived from the results of the simpler systems are used to assist the assignment of kinetic parameters to the 21 permutation reactions of the six types of isomeric peroxy radical generated in the isoprene system. Kinetic models describing the OH-initiated degradation of all three conjugated dienes to first generation products in the absence of NOx are recommended, which are also consistent with available end product studies. The model for isoprene is considered to be a further improvement on that suggested previously for its OH-initiated oxidation in the absence of NOx. The mechanism is further extended to include chemistry applicable to ‘NOx-present’ conditions, and calculated product yields are compared with those reported in the literature.

Peroxy Radical Kinetics Resulting from the OH-Initiated Oxidation of 1,3-Butadiene, 2,3-Dimethyl-1,3-Butadiene and Isoprene

Transient species in the photooxidation of formaldehyde in air have been investigated by using the technique of flash photolysis kinetic spectroscopy. The absorption spectrum attributed to the HOCH{sub 2}O{sub 2} radical was observed with a maximum near 230 nm. This radical is formed by the reaction HO{sub 2} + HCHO {Longleftrightarrow} HOCH{sub 2}O{sub 2} (1, -1). The rate constants were measured for the two reactions: k{sub 1} = 7.7 {times} 10{sup {minus}15} exp((625 {plus minus} 550)/T) cm{sup 3} molecule{sup {minus}1} s{sup {minus}1} and k{sub {minus}1} = 2.0 {times} 10{sup 12} exp(({minus}7000 {plus minus} 2000)/T) s{sup {minus}1}. The equilibrium constant is K{sub 1}* = 3.85 {times} 10{sup {minus}27} exp(7625/T) cm{sup 3} molecule{sup {minus}1}, which corresponds to a reaction enthalpy {Delta}H{sub 1}{degree} = {minus}16.25 {plus minus} 0.30 kcal mol{sup {minus}1}, which is based on the K{sub p} value and quantum calculations of {Delta}S{sub 0}{degree} and therefore determined accurately. Kinetic measurements performed under various experimental conditions allowed determinations of the rate constants for the reactions HO{sub 2} + HOCH{sub 2}O{sub 2} {yields} products (3) and 2HOCH{sub 2}O{sub 2} {yields} O{sub 2} + CH{sub 2}(OH){sub 2} + HCOOH (4b); k{sub 3} = 5.6 {times} 10{sup {minus}15} exp((2300 {plus minus} 1100)/T); k{sub 4b} = 5.65more » {times} 10{sup {minus}14} exp((750 {plus minus} 400)/T) cm{sup 3} molecule{sup {minus}1} s{sup {minus}1}. The branching ratios for k{sub 3} and k{sub 4} were determined in separate experiments described in part 2 of this work.« less

Kinetics and mechanism of the photo-oxidation of formaldehyde. 1. Flash photolysis study

The kinetics of the thermal decomposition and formation reactions of acetyl peroxynitrate (PAN) CH{sub 3}C(O)O{sub 2} + NO{sub 2} + M {leftrightarrow} CH{sub 3}C(O)O{sub 2}NO{sub 2} + M (1, {minus}1) was studied as a function of temperature and pressure by two groups. In one set of experiments, the decomposition of the peroxynitrate formed in the photolysis of CH{sub 3}CHO/Cl{sub 2}/O{sub 2}/N{sub 2}/NO{sub 2} mixtures was followed by in situ FTIR spectrometry. In the second set of experiments, the decay of the acetylperoxy radical formed in the flash photolysis of Cl{sub 2}/CH{sub 3}CHO/NO{sub 2}/air mixtures was monitored by UV absorption. From the two independent kinetic determinations of k{sub 1} and k{sup {minus}1}, the equilibrium constant K{sub 1}(T) was calculated to be 0.9 {times} 10{sup {minus}28} exp((14,000 {plus minus} 200)/T) cm{sup 3} molecule{sup {minus}1}. Quantum chemical and RRKM calculations were performed to obtain accurate and predictive representations of the data. In Troe's notation, the RRKM curves corresponding to the experimental results are represented by the following expressions for the limiting low- and high-pressure rate constants, with F{sub c} = 0.30: k{sub 0}({minus}1) = 4.9 {times} 10{sup {minus}3} exp({minus}(12,100 {plus minus} 500)/T) cm{sup 3} molecule{sup {minus}1} s{sup {minus}1}; k{sub {infinity}}({minus}1) = 4.0 {times}more » 10{sup 16} exp({minus}(13,600 {plus minus} 350)/T) s{sup {minus}1}; k{sub 0}(1) = 2.7 {times} 10{sup {minus}28}(T/298){sup {minus}7.1{plus minus}1.7} cm{sup 6} molecule{sup {minus}2} s{sup {minus}1}; k{sub {infinity}}(1) = (12.1 {plus minus} 0.5) {times} 10{sup {minus}12}(T/298){sup {minus}0.9{plus minus}0.15} cm{sup 3} molecule{sup {minus}1} s{sup {minus}1}. The thermochemistry of reactions 1 and {minus}1 and the atmospheric implications of the thermal stability of PAN are briefly discussed.« less

Kinetic and theoretical studies of the reactions acetylperoxy + nitrogen dioxide + M .dblarw. acetyl peroxynitrate + M between 248 and 393 K and between 30 and 760 torr

Robert Lesclaux

Papers

Atmospheric chemistry of small organic peroxy radicals

Peroxy Radical Kinetics Resulting from the OH-Initiated Oxidation of 1,3-Butadiene, 2,3-Dimethyl-1,3-Butadiene and Isoprene

Kinetics and mechanism of the photo-oxidation of formaldehyde. 1. Flash photolysis study

Kinetic and theoretical studies of the reactions acetylperoxy + nitrogen dioxide + M .dblarw. acetyl peroxynitrate + M between 248 and 393 K and between 30 and 760 torr

Kinetics of the reaction of HO2 with CH3C(O)O2 in the temperature range 253–368 K