Impacts of regional transport and boundary layer structure on the PM2.5 pollution in Wuhan, Central China

Wuhan, one of the most developed cities in Central China, has been experiencing frequent heavy haze pollution. To understand the impacts of large-scale synoptic patterns and the local-scale planetary boundary layer (PBL) structures on the PM2.5 pollution in Wuhan, this study applied an objective approach to the classifying of the daily synoptic patterns in 2017. It then combined observational analyses and meteorology-chemistry coupled simulations to investigate a typical pollution episode at the end of November 2017. The synoptic type associated with the heaviest PM2.5 pollution in Wuhan was characterized by high pressure to the northwest and low pressure to the northeast at the 850-hPa level, which can support northwesterly prevailing winds towards Wuhan. As a result, the aerosols from the highly polluted northern regions can be transported to Wuhan, leading to a high PM2.5 concentration. Also, when there was high pressure located to the east/southeast of Wuhan at the 850-hPa level, southerly warm advections could be induced. The warming of upper air can significantly suppress the development of PBL by enhancing thermal stability, favoring the accumulation of aerosols. This study elucidated the multi-scale physical mechanisms underlying the aerosol pollution in Wuhan, and has important implications for the forecasting and the mitigating of pollution.