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In order to investigate the variation characteristics of atmospheric aerosols under precipitation, total suspended particulates (TSP) and fine aerosols (PM 2.5 ) under a series of rain events were collected at Ya'an, a famous rain city in western China. The mass, ionic composition and acidity of aerosols on the non-rainy days (before the rain) and on the rainy days were analyzed. Results showed that the mass concentrations of TSP and PM 2.5 were both higher on the rainy days than on non-rainy days, the increasing rates were 43% and 11% respectively, illustrating an effective uptake of particle mass from upper air to low level by rainfall as well as the mild scavenging of aerosol components during the light rain. Total concentrations of water soluble ions in two kinds of aerosols (TSP and PM 2.5 ) were also obviously increased on rainy days, the increasing rates were 63% and 50% respectively. Moreover, NO 3 -, NH 4 + and C 2 O 4 2-presented a great increasing trend among all water soluble ionic species undergoing the rain, implying an important gaseous transforming process into particle phase under precipitation. Acidity measurement demonstrated that the aerosol acidity under rainy days was also higher than those under non-rainy days, possibly due to obvious scavenging of alkaline components in the ambient aerosols during precipitation.