Long-term Variations in Winter PM10 Concentrations over East Asia Influenced by Large-scale Atmospheric Circulations

Concentrations of wintertime particulate matters of diameters smaller than 10 μm (PM₁₀) in South Korea and China have decreased since the 2000s owing to the air pollution reduction policies of the two countries; however, this decreasing tendency has been significantly weakened, or even been reversed, in recent years. This study examined the influence of large-scale atmospheric circulations on this PM₁₀ changes over East Asia for the winters (December–February) of the 2004/05–2015/16 period using an empirical orthogonal function (EOF) analysis. The first EOF mode, which accounts for 32.7% of the total variance, shows decreases in PM₁₀ concentrations until 2012 and thereafter increases in them particularly at most stations in eastern and northeastern China. Regression patterns of meteorological variables with respect to the first EOF time series indicate that the wintertime PM₁₀ variations over East Asia are greatly influenced by the Ural blocking; the weakening of the Ural blocking after 2014 led to the weakening of cold air flows from the north to provide atmospheric conditions favorable for bad air quality events over East Asia. The second EOF mode, which accounts for 20.1% of the total variance, shows a similar spatial distribution to the linear trend of the PM₁₀ concentrations in the analysis period, implying the relationship with the changes in pollutant emissions. Our findings emphasize that the long-term variations in air quality over East Asia are affected primarily by the variations in the large-scale atmospheric circulations with secondary contributions from the local emission changes.