Abstract. A high O 3 episode with the large increases in surface ozone by 21-42 ppbv and the nocturnal surface O 3 levels exceeding 70 ppbv was observed in the region between Xiamen and Quanzhou over the southeastern coast of China during 12-14 June 2014, before the Typhoon Hagibis landing. Variations in the surface O 3 , NO 2 , CO and meteorology during the Typhoon Hagibis event clearly suggest a substantial impact of the peripheral downdrafts in the large-scale typhoon circulation on such an O 3 episode excluding the contributions of photochemical production and the horizontal transport. The influence of vertical O 3 transport from the upper troposphere and lower stratosphere (UTLS) region on high surface O 3 levels is further confirmed by a negative correlation between surface O 3 and CO concentrations as well as dry surface air observed during the O 3 episode. This study provides observational evidence of typhoon-driven intrusion of O 3 from the UTLS region to surface air, revealing a significant effect of such a process of stratosphere-troposphere exchange (STE) of O 3 on tropospheric O 3 and ambient air quality.

Abstract. Rapid increases in pollutant emissions in conjunction with stagnant meteorological conditions result in haze pollution in China. Recent frequent haze in China has attracted worldwide attention. Here we show a relationship between the haze events and Tibetan Plateau (TP)'s environment and climate changes. Based on observational data taken over recent decades, we identify central-eastern China (CEC) as a climatological large-scale "susceptible region" of frequent haze, which is harbored by the TP with its impact on midlatitude westerly winds. The observational and modeling studies demonstrate that the interannual variations in the thermal forcing of TP are positively correlated with the incidences of wintertime haze over CEC. Further analysis indicates that the climate warming of the TP induced changes in atmospheric circulation, driving frequent haze events in CEC. The frequent haze occurrences in CEC are consistent with decreasing winter monsoon winds, intensifying downward air flows and increasing atmospheric stability in the lower troposphere over the CEC in association with upstream plateau's thermal anomalies. Therefore, variations of haze in China are related to mechanical and thermal forcing by the TP. Our results also suggest that implications of the large TP topography for environment and climate changes should be taken into account for air pollution mitigation policies in China.

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