Abstract
Abstract. A regional fully coupled meteorology–chemistry model, Weather Research and Forecasting model with Chemistry (WRF-Chem), was employed to study the seasonality of ozone (O3) pollution and its sources in both China and India. Observations and model results suggest that O3 in the North China Plain (NCP), Yangtze River Delta (YRD), Pearl River Delta (PRD), and India exhibit distinctive seasonal features, which are linked to the influence of summer monsoons. Through a factor separation approach, we examined the sensitivity of O3 to individual anthropogenic, biogenic, and biomass burning emissions. We found that summer O3 formation in China is more sensitive to industrial and biogenic sources than to other source sectors, while the transportation and biogenic sources are more important in all seasons for India. Tagged simulations suggest that local sources play an important role in the formation of the summer O3 peak in the NCP, but sources from Northwest China should not be neglected to control summer O3 in the NCP. For the YRD region, prevailing winds and cleaner air from the ocean in summer lead to reduced transport from polluted regions, and the major source region in addition to local sources is Southeast China. For the PRD region, the upwind region is replaced by contributions from polluted PRD as autumn approaches, leading to an autumn peak. The major upwind regions in autumn for the PRD are YRD (11 %) and Southeast China (10 %). For India, sources in North India are more important than sources in the south. These analyses emphasize the relative importance of source sectors and regions as they change with seasons, providing important implications for O3 control strategies.
Highlights
Tropospheric ozone (O3) is the third most potent greenhouse gas in the atmosphere (IPCC, 2007), an important surface air pollutant, and the major source of the hydroxyl radical
The present study adopted the ozone tagging method implemented in WRF-Chem by Gao et al (2017a), which is similar to the ozone source apportionment technology (OSAT; Yarwood et al, 1996) approach implemented in the Comprehensive Air Quality Model with Extensions (CAMx)
To further address the issue of nighttime titration effects, we calculated the sensitivity of daytime O3 formation in July to the different sectors, and we found that daytime O3 in the North China Plain (NCP) and Yangtze River Delta (YRD) are most sensitive to industrial and biogenic emissions (Table 4)
Summary
Tropospheric ozone (O3) is the third most potent greenhouse gas in the atmosphere (IPCC, 2007), an important surface air pollutant, and the major source of the hydroxyl radical (a key oxidant playing an essential role in atmospheric chemistry). With respect to the enhanced concentrations of O3 over the past years, Sun et al (2019) attributed them to elevated emissions of anthropogenic volatile organic compounds (VOCs), while Li et al (2019) argued that an inhibited aerosol sink for hydroperoxyl radicals induced by decreased PM2.5 over 2013–2017 played a more important role in the North China Plain (NCP). Despite this progress, the seasonal behaviors of O3 in different regions greatly differ, yet they have not been intercompared and the underlying causes have not been comprehensively explored.
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