Multi-scale analysis of the impacts of meteorology and emissions on PM2.5 and O3 trends at various regions in China from 2013 to 2020 1: Synoptic circulation patterns and pollution.

A multiscale analysis of meteorological trends was carried out to investigate the impacts of the large-scale circulation types as well as the local-scale key weather elements on the complex air pollutants, i.e. PM2.5 and O3 in China. As the first paper in the series, the relationship between synoptic circulation patterns and pollution was investigated. Six types of circulation patterns are defined and clustered to correlate with the observed pollutant levels, resulting in the identification of the impact similarity and difference of circulations on PM2.5 and O3 for three regions in China, i.e., the BTH (Beijing, Tianjin and Hebei), YRD (Yangtze River Delta) and PRD (Peral River Delta), from 2013 to 2020. It is found that the six clustered circulation patterns were able to classify the circulation patterns that influence the pollutants and yield significant correlations with O3 and PM2.5 in three regions. The major circulation patterns governing the heavy PM2.5 and O3 were identified separately for each region and found to show inter-annual variabilities. Composite analysis indicated that there were some circulation patterns that caused the dual-highs of PM2.5 and O3 with about 13%, 8% and 3% occurrences during the period of 2013 to 2020 in Beijing, Shanghai and Guangzhou, respectively. The key weather elements for each type of circulation pattern were also identified. A detailed study of the impacts of key weather elements and emissions on the PM2.5 and O3 trends will accompany this paper (Gong et al., 2022).