The Goddard Earth Observing System with chemistry (GEOS-Chem) model has been updated with the State-wide Air Pollution Research Center version 11 (SAPRC-11) aromatics chemical mechanism, with the purpose of evaluating global and regional effects of the most abundant aromatics (benzene, toluene, xylenes) on the chemical species important for tropospheric oxidation capacity. The model evaluation based on surface and aircraft observations indicates good agreement for aromatics and ozone. A comparison between scenarios in GEOS-Chem with simplified aromatic chemistry (as in the standard setup, with no ozone formation from related peroxy radicals or recycling of NO x ) and with the SAPRC-11 scheme reveals relatively slight changes in ozone, the hydroxyl radical, and nitrogen oxides on a global mean basis (1%-4%), although remarkable regional differences (5%-20%) exist near the source regions. NO x decreases over the source regions and increases in the remote troposphere, due mainly to more efficient transport of peroxyacetyl nitrate (PAN), which is increased with the SAPRC aromatic chemistry. Model ozone mixing ratios with the updated aromatic chemistry increase by up to 5ppb (more than 10%), especially in industrially polluted regions. The ozone change is partly due to the direct influence of aromatic oxidation products on ozone production rates, and in part to the altered spatial distribution of NO x that enhances the tropospheric ozone production efficiency. Improved representation of aromatics is important to simulate the tropospheric oxidation.
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Acknowledgements. This research is supported by the National Natural Science Foundation of China (41775115), the 973 program (2014CB441303), and the Key Program of Ministry of Science and Technology of the People’s Republic of China (2016YFA0602002; 2017YFC0212602). The research was also funded by the Start-up Foundation for Advanced Talents (162301182756). We acknowledge the free use of ozone data from networks of WDCGG (http://ds.data.jma.go.jp/gmd/wdcgg/ cgi-bin/wdcgg/catalogue.cgi; last access: 28 December 2018) and EMEP (http://www.nilu.no/projects/ccc/emepdata.html; last access: 28 December 2018) and aromatic compound observations from EEA (http://www.eea.europa.eu/data-and-maps/data/ airbase-the-european-air-quality-database-8; last access: 28 December 2018) and EMEP. We also want to thank Angela Baker for providing the CARIBIC data. Dylan B. Millet acknowledges support from NASA (grant no. NNX14AP89G).