The impact of synoptic circulation and long-term circulation change on air quality and pollution-related human health in the Yangtze River Delta region

We extend previous synoptic-scale work to climatological scale to examine the potential effects of long-term circulation changes on surface air quality and pollution-related public health in the Yangtze River Delta (YRD) region. This climatological-scale study detects the long-term circulation trends based on the Lamb weather type technique, quantifies the circulation change-driven PM_2.5 and O₃ changes using a synoptic downscaling statistical approach, and assesses the circulation change-induced air quality impact on acute mortality using the health impact assessment (HIA) model. The results indicate that synoptic circulation influencing the YRD region experienced a significant decline in negative vorticity during the period from 1979 to 2017. Consequently, the frequency of the anticyclonic pattern decreased by 17.6% from 32.9% in the historical period (1979-83) to 27.1% in the current period (2013-17), and the total occurrence of easterly patterns increased by 33.6%. The long-term circulation changes potentially caused a decrease in the annual PM_2.5 concentration of 1.0-3.0µg/m³ (a regional mean decrease of 2.0µg/m³) over the YRD region; but a relatively modest O₃ change (a regional mean increase of 0.4µg/m³). These circulation-driven air quality changes (especially PM_2.5 change) can be largely explained by the changing transport effects due to weakened East Asian winter monsoon (i.e., increased clean marine sources and decreased polluted continental sources). The increased O₃ caused 217 (95% CI: 172, 262) annual acute deaths, but this “climate penalty” was offset by the larger avoided mortality due to the circulation-driven PM_2.5 reduction. Overall, long-term circulation changes were responsible for averting 448 (95% CI: 395, 561) annual acute deaths in the YRD region, which suggests a public health “climate benefit.” These findings are anticipated to provide important information for regional climate and air quality forecast, as well as public health management.