Spatial features of rain frequency change and pollution and associated aerosols

Abstract. A spatial-temporal analysis has been conducted using satellite observed distributions of rain frequency, NO₂ concentration and aerosol, with focus on the spring season in East Asia. As NO₂ is a key precursor of secondary aerosols, especially in urban areas, an increase of NO₂ emission is generally accompanied by an increase of fine aerosol particles. Comparison between trends in rain frequency and in precipitation amount shows that the changes in precipitation are more due to changes in precipitation occurrence than in precipitation amount. The overall feature emerged from the region-by-region analyses is that there is an inverse relationship between the rain frequency and the pollution and associated aerosols at continental scale in spring. The change in rain frequency is associated with changes in pollution-produced aerosols and long-range transport mineral dust. The inverse relationship at large temporal and spatial scales illustrates potential climatological consequence of changed pollution and aerosols on precipitation. Due to relatively short duration of observation and the potential uncertainty and bias associated with satellite measurements, more robust longer-term statistical study at various temporal and spatial scales and detailed modeling investigation are warranted to understand the physical causality of observed relationship between the rain frequency and the pollution and associated aerosols.