Evaluation of air quality changes in a Chinese megacity over a 15-year period (2006-2021) using PM receptor modelling.

Air quality impairment has a massive impact on human health, with atmospheric particulate matter (PM) playing a major role. The People's Republic of China experienced a trend of increasing PM concentrations from 2000 to 2013. However, after the application of the Air Pollution Prevention and Control Action Plan and other related control measures, sharp decreases in air pollutant concentrations were particularly evident in the city of Wuhan (central China). This study analysed major changes in PM concentrations, composition and source apportionment (using receptor modelling) based on Wuhan's PM chemical speciation datasets from 2006 to 2007, 2019-2021 and contemporaneous gaseous pollutant values. Average SO concentrations decreased by 88%, from the first to the second period, mostly due to measures that reduced coal combustion. However, NO only declined by 25%, with policy measures likely being undermined by an increased number of vehicles. PM concentrations decreased by 65%, with the PM constituents each being affected differently. Coal combustion-related element concentrations, OC, SO, NH, EC, Cl, Al, Ca, Cu, Fe, Co and NO decreased by 22-90%. Secondary inorganic aerosol (SIA) was initially dominated by (NH)SO (73%) in 2006, but later dominated by NHNO (52%) in 2021. Receptor modelling identified major sources contributing to PM: Mineral, road and desert dust (MRDD), Secondary sulphate (SECS), Secondary nitrate (SECN), Tungsten industry (W), Toxic Elements of Coal (TEC), Iron and Steel (IRONS), Coal Combustion (CC), Residential Heating (RH), Refinery (REF) and Traffic (TRF). In relative proportions, TEC (-83%), SECS (-64%) and SECN (-48%) reduced their contributions to PM whilst MRDD increased (+62.5%). Thus, the results indicate not only a drastic abatement of PM pollution in Wuhan but also a change in the sources of pollution, which requires further actions to reduce PM concentrations to health protective values. Secondary PM and fugitive emissions are key components to abate.