The case study of impacts of Tehran ambient air pollution on the cloud and precipitation characteristics

Concentration and type of atmospheric aerosols are among of the most important factors affecting the macro and micro structure of clouds and their precipitation.
In this article, the case study has been carried out to investigate the relationship between atmospheric air pollution, microphysics of cloud and their precipitation over Tehran city. The case study in this paper (2012/12/06) was performed before the the rainfall that increased AQI index for particulate matter which made Tehran to be closed for two days. This event was compared with two similar rainfalls shortly before or after it and it was found out that in the two similar rainfalls the AQI index had been healthy during the days before precipitation. Ion concentrations in the rainwater were measured by ion-chromatography and microphysics of clouds were studied by MODIS on board Aqua and Terra satellite.
Findings: The results showed that ions concentration, especially anthropogenic ions (nitrate, nitrite, chloride and fluoride), in rainwater samples in polluted air was higher than in clear air. Also particulate pollution reduced the effective radius droplet of the mixed-phase clouds before the rain, and increased the cloud optical thickness, cloud water path and cloud top pressure and temperature during the precipitation.
Discussion and The ions in rain water and the cloud microphysics characteristics related to the concentration of aerosols in the atmosphere. Also, local particle pollutions changed regional microphysics of cloud