Impact of Western Pacific Subtropical High on Ozone Pollution over Eastern China

Abstract:

Surface ozone is a major pollutant in Eastern China, especially during the summer season. The formation of surface ozone pollution highly depends on meteorological conditions as generally controlled regional circulation patterns. Here we show that summertime ozone pollution over Eastern China is distinctly modulated by the variability of West Pacific Subtropical High (WPSH), a major synoptic system that controls the summertime weather conditions of East Asia. Composite and regression analyses indicate that positive WPSH anomaly is associated with higher than normal surface ozone concentration over Northern China but lower ozone over Southern China. We show that this is mainly driven by changes in meteorological variables with stronger than normal WPSH leading to higher temperature, stronger solar radiation at land surface, lower relative humidity, and less precipitation in Northern China, favoring the production and accumulation of surface ozone. In contrast, all variables show reverse changes in Southern China under stronger WPSH. GEOS-Chem simulations reasonably reproduce the observed ozone changes associated with the WPSH and support the statistical analyses. Detailed contributions of difference processes are quantified through budget diagnosis, which emphasizes the decisive role of chemistry. Natural emission of precursors from biogenic and soil sources account for ~30% of the total surface ozone changes.