Impact of Weather Patterns and Meteorological Factors on PM2.5 and O3 during the Covid-19 Lockdown in China
Abstract. The abnormal haze event in NCP (North China Plain) and the decline in ozone levels in SC (Southern China) from 21st January to 9th February 2020 have attracted public curiosity and scholarly attention during the COVID-19 lockdown. Most previous studies focused on the impact of atmospheric chemistry processes associated with anomalous weather elements in these cases, but fewer studies quantified the impact of various weather elements within the context of a specific weather pattern. To identify the weather patterns responsible for inducing this unexpected situation and to further quantify the importance of different meteorological factors during the haze event, two scenarios are employed. These scenarios compared observations to climatology averaged over the years 2015–2019 and the ‘Business As Usual’ (hereafter referred to as BAU) emission strength, using a novel structural SOM (Self-Organising Map) and ML (Machine Learning) models. The results reveal that the unexpected PM2.5 pollution and O3 decline from the climatology in NCP, North East China (NEC), and SC could be effectively explained by the presence of a double-centre high-pressure system. Moreover, the ML results provided a quantitative assessment of the importance of each meteorological factor in driving the predictions of PM2.5 and O3 under the specific weather system. These results indicate that temperature played the most crucial role in the haze event in NCP and NEC, as well as in the O3 decline in SC. This valuable information will ultimately contribute to our ability to predict air pollution under future emission scenarios and changing weather patterns that may be influenced by climate change.
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