Evolution, Transport Characteristics, and Potential Source Regions of PM2.5 and O3 Pollution in a Coastal City of China during 2015–2020

Abstract

The evolution, transport characteristics, and potential source regions of PM2.5 and O3 were investigated from 1 January 2015 to 31 December 2020 in the coastal city of Nantong. The annual mean PM2.5 concentration declined obviously over the entire study period, and was 34.7 μg/m3 in 2020. O3 had a relatively smooth decreasing trend, but rebounded greatly during 2017 when the most frequent extreme high-temperature events occurred. Similar trends were observed for PM2.5 and O3 polluted hours. No PM2.5-O3 complex air pollution happened in 2019 and 2020, likely suggesting the preliminary results from the implementation of emission controls. Notable differences in transport pathways and frequencies were observed from the backward trajectory clusters in four seasons in Nantong. Clusters with the largest percentage of polluted PM2.5 and O3 trajectories were transported mostly over short distances rather than long distances. Analysis involving the potential source contribution function (PSCF) and concentration weighted trajectory (CWT) showed that PM2.5 polluted sources were from the adjacent western and northwestern provinces, whereas the influence of eastern marine sources was relatively small. O3 had a greatly different spatial distribution of polluted source regions from PM2.5, mostly covering the North China Plain, the Bohai Sea, and the Yellow Sea.