Sensitivity analysis of atmospheric oxidation capacity in Beijing based on the GRAPES-CUACE adjoint model

Abstract

In this study, based on the evaluation index of atmospheric oxidation capacity (AOIe), the GRAPES-CUACE atmospheric chemistry model was used to simulate and analyze the variation characteristics of atmospheric oxidation capacity (AOC) in Beijing during typical pollution processes in each season in 2017. The sensitivity analysis of the AOIe in Beijing was further conducted using the GRAPES-CUACE adjoint model, and the contribution of precursor emissions in Beijing and surrounding areas to the AOIe in Beijing was quantitatively evaluated. The findings revealed that, on average, Beijing's AOC was strongest in summer, followed by spring and autumn, and weakest in winter. The contribution of oxidation capacity of gaseous-phase oxidation products (AOIe_G) to AOIe was dominant in all seasons, and the oxidation capacity of particle-phase oxidation products (AOIe_P) contributed a relatively larger proportion during PM2.5 pollution periods in winter. Adjoint sensitivity analysis showed that the Beijing peak AOIe value was controlled by both NOx and VOCs in summer, VOCs in winter, and somewhere in between in spring and autumn. Overall, Beijing and Hebei emissions contributed the most to the Beijing peak AOIe value, with a combined contribution of 63–83.6%, while Tianjin, Shanxi, and Shandong emissions also made a non-negligible contribution. In terms of emission source types, VOCs emissions contributed the most to the Beijing peak AOIe value (42.9–79.4%); NOx emissions contributed the most in summer (43.1%) and the least in winter (16.5%); CO emissions contributed a proportion of 4–17.4%. These results further demonstrate that the AOIe index is an appropriate indicator to quantify AOC, laying the foundation for subsequent research based on AOIe. Besides, this study provides more refined results on the sensitivity of AOIe in Beijing to precursor emissions and detects the critical emission sources and their contributions to AOIe in Beijing, which is conducive to a more comprehensive understanding of AOC and improving air quality in Beijing.