Abstract
Abstract. Aromatic hydrocarbons, including benzene, toluene, and xylenes, play an important role in atmospheric chemistry, but the associated chemical mechanisms are complex and uncertain. Sparing representation of this chemistry in models is needed for computational tractability. Here, we develop a new compact mechanism for aromatic chemistry (GC13) that captures current knowledge from laboratory and computational studies with only 17 unique species and 44 reactions. We compare GC13 to six other currently used mechanisms of varying complexity in box model simulations of environmental chamber data and diurnal boundary layer chemistry, and show that GC13 provides results consistent with or better than more complex mechanisms for oxygenated products (alcohols, carbonyls, dicarbonyls), ozone, and hydrogen oxide (HOx≡OH+HO2) radicals. Specifically, GC13 features increased radical recycling and increased ozone destruction from phenoxy–phenylperoxy radical cycling relative to other mechanisms. We implement GC13 into the GEOS-Chem global chemical transport model and find higher glyoxal yields and net ozone loss from aromatic chemistry compared with other mechanisms. Aromatic oxidation in the model contributes 23 %, 5 %, and 8 % of global glyoxal, methylglyoxal, and formic acid production, respectively, and has mixed effects on formaldehyde. It drives small decreases in global tropospheric OH (−2.2 %), NOx (≡NO+NO2; −3.7 %), and ozone (−0.8 %), but a large increase in NO3 (+22 %) from phenoxy–phenylperoxy radical cycling. Regional effects in polluted environments can be substantially larger, especially from the photolysis of carbonyls produced by aromatic oxidation, which drives large wintertime increases in OH and ozone concentrations.
Highlights
Aromatic hydrocarbons are a major class of volatile organic compounds (VOCs) emitted to the atmosphere, with important effects on oxidant chemistry and secondary organic aerosol (SOA) formation
We evaluate GEOS-Chem version 13 (GC13) in box model simulations of laboratory chamber experiments and the continental boundary layer and compare it to six other mechanisms used in atmospheric models: the Common Representative Intermediates (CRI) mechanism, the Master Chemical Mechanism (MCM), the Module Efficiently Calculating the Chemistry of the Atmosphere (MECCA), the Model for Ozone and Related chemical Tracers (MOZART), the Regional Atmospheric Chemistry Mechanism (RACM2), and the Statewide Air Pollution Research Center (SAPRC) mechanism
We developed a new compact mechanism (GC13) for fast and accurate simulation of benzene, toluene, and xylene (BTX) oxidation chemistry in atmospheric models
Summary
Aromatic hydrocarbons are a major class of volatile organic compounds (VOCs) emitted to the atmosphere, with important effects on oxidant chemistry and secondary organic aerosol (SOA) formation. They are emitted from anthropogenic sources, including incomplete combustion, industrial processes, solvent evaporation, and fuel leakage (Na et al, 2004; Reimann and Lewis, 2007), and have additional sources from biomass burning and vegetation (Misztal et al, 2015; Cabrera-Perez et al, 2016). The importance of aromatics for ozone formation spurred the initial development of BTX oxidation mechanisms for air quality models (Carter, 1990; Stockwell et al, 1997). We implement GC13 into GEOS-Chem, a global chemical transport model (CTM), to diagnose the effects of aromatic chemistry in the troposphere on oxygenated organics and oxidant chemistry
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