Source apportionment of summertime ozone in China using a source-oriented chemical transport model
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2019 Elsevier Ltd Contributions of industries, power plants, residential, transportation, open burning, and biogenic sectors to summertime ozone (O3)in China in August 2013 are quantified using an improved O3 source apportionment method implemented in a source-oriented Community Multiscale Air Quality (CMAQ)model. The new O3 source apportionment method attributes in-situ O3 formed in each time step to nitrogen oxides (NOx)and volatile organic compounds (VOCs)with a new attribution scheme that considers NOx-VOC-O3 formation sensitivity in NOx-limited, transition, and VOC-limited regimes (three regimes, 3R). This represents an improvement from the traditional O3 source apportionment models, in which O3 formation sensitivity is divided into two-regimes (2R), either NOx-limited or VOC-limited. An expanded source-oriented gas phase chemical mechanism is developed to concurrently track NOx and primary VOCs and their oxidation products from different sources. The source-resolved NO2 photolysis rates and the NO to NO2 conversion rates by peroxy radicals from the source-oriented chemical mechanism are then used to apportion O3 to NOx (O3_NOx)and VOCs (O3_VOC)from different emission sources. Industries, transportation, power plants and biogenic sources are the major emission sectors to O3. High industrial O3_NOx (815 ppb; 2025% of total O3)is mainly located in north and northeast China, the Yantze River Delta (YRD)and part of the Sichuan Basin (SCB). Transportation O3_NOx accounts for 1015% of total O3 in most urban areas. Power plants contributions to O3_NOx (1015%)are mostly located in Shanxi, Shaanxi, Ningxia and part of Shandong and Jiangsu. The contribution of soil NOx to O3_NOx is highest in regions in west, central and south China with less direct anthropogenic emission influences. VOC-limited grid cells are mostly located at urban cores and large city clusters in the YRD and Pearl River Delta (PRD)regions. Biogenic and industrial sectors are the most important emission sectors that contribute to O3_VOC, accounting for more than 85% of the O3_VOC in China. In north and east provinces, more than 50% of the O3 is non-background, with the provinces in north China having higher overall O3. The Beijing-Tianjin-Hebei (BTH)region has an area-averaged 8-hr O3 of 75 ppb in August 2013 and about half is non-background. Contributions of industries, transportation, power and biogenic sources to non-background O3 are 37%, 22%, 13% and 23%, respectively. The relative contribution of biogenic emissions to non-background O3 is lower on high 8-hr O3 days. The 2R and 3R approaches show significant differences in assessing the relative importance of O3_NOx and O3_VOC, with the 2-regime approach predicting lower O3_NOx but higher O3_VOC. The new source allocation method for O3_VOC can lead to up to 10% differences for industrial and biogenic sectors.
