Implications of the extremely hot summer of 2022 on urban ozone control in China

Abstract

Frequent occurrences of extreme heat are causing severe ozone pollution over China. This study examined the driving factors of urban ozone pollution in China during the extremely hot summer of 2022 and the impact of emission control strategies using surface measurements and the GEOS-Chem model. The results show that ozone pollution was extremely severe in summer 2022, with a significant rebound by 12–15 ppbv in the North China Plain (NCP), Yangtze River Delta (YRD), and Sichuan basin (SCB), compared to 2021. Especially over the NCP, the MDA8 (maximum daily 8-hourly average) ozone exceeded 160 ppbv, and the number of ozone exceedances was over 42 days. Based on an IPR (integrated process rate) analysis, the authors found that the net chemical production was the dominant factor contributing to the strong ozone increase in summer 2022. For example, in June over the NCP, the net chemical production resulted in an increase by 3.08 Gg d⁻¹ (∼270%) in ozone mass change. Sensitivity simulations showed that both NO_x (nitrogen oxides) and VOC (volatile organic compound) reductions were important over the NCP, and NO_x reductions were more important than VOCs over southern China. To keep the ozone of 2022 at the same level as 2021, a joint reduction of NO_x and VOCs by at least 50%–60% would have been required. This study highlights the urgency to develop effective ozone management since extreme heat will become more frequent.

摘要

本文利用地面观测和数值模式研究了2022年夏季极端高温下我国城市臭氧污染的控制策略. 研究表明, 2022年夏季臭氧污染极为严重, 相较于2021年有显著的反弹, 其中华北, 长三角和四川盆地的月均臭氧上升12–15 ppbv. 模式过程分析结果表明净化学生产是高温时造成臭氧浓度升高的主导因素. 模式多组敏感性试验表明, 华北地区需要NO_x和VOC协同控制, 南方城市需要侧重对NO_x排放管控, 并且需要对NO_x和VOC协同减排至少50%–60% 才会使2022年夏季臭氧污染水平与2021年一致. 在极端高温愈发频繁的形势下, 本研究强调未来亟需研究更为有效的臭氧调控策略.