Impacts of long-range transports from Central and South Asia on winter surface PM2.5 concentrations in China

Highlights: • The long-range transport from upstream increases the PM_2.5 concentration in China. • The average increment of PM_2.5 is decreased (increased) during El Niño (La Niña). • The CBC in WRF-Chem converted from MOZART4 might overestimate dust concentration. A quantitative analysis of the impacts of particulate matter transported from Central and South Asia on winter surface PM_2.5 concentrations in China is investigated from 2013 to 2017. The chemical boundary conditions generated by the MOZART4 global model (MOZ-CBC) are used to drive WRF-Chem regional model as the long-range transport inflow to China. The long-range transport effects of PM_2.5 were estimated by the difference caused by primary aerosol (PA), secondary aerosol (SIA), and dust separately from the corresponding component changes in MOZ-CBC. On the five-year average, the long-range transports of particulate matter increase the winter surface dust concentrations by 6–30 μg/m³, PA concentrations by 0–2 μg/m³, and SIA concentrations by 0–1.2 μg/m³. Except for Xinjiang, which is closest to the western border, North China Plain is the most significant region in the mainland of China that could be affected by the long-range transport, indicated by the average increase at 1.6 μg/m³ (4.5%) in PA, 0.9 μg/m³ (1.8%) in SIA, and 16 μg/m³ (35%) in dust. The average increment in PA, SIA, and dust is decreased during El Niño and increased during La Niña. Wind anomalies in the El Niño event weaken prevailing westerly wind but favor the meridional circulation, increasing the precipitation and wet scavenging contribution in the eastern seaboard and resulting in the decrease of the PM_2.5 concentration in China caused by long-range transport, while these phenomena are opposite in La Niña events. However, the MOZART4 model might overestimate the frequency of dust storms in winter and the vertical height that dust could reach.