Scavenging efficiency of water soluble inorganic and organic aerosols by fog droplets in the Indo Gangetic Plain

Abstract The interaction of aerosols with fog droplets impacts the processing and scavenging of ambient particles. It is essential to know about such interaction for refining the regional model description of particles lifetime. Towards this, we performed simultaneous collection of aerosol and fog water samples during winter period at a rural location of Indo Gangetic Plain. These samples were analyzed for water soluble inorganics ions and organic carbon (WSOC) and heavy metals. The results showed that aerosol and its water soluble constituent's concentration get reduced during foggy nights compared to non-foggy nights, due to the scavenging of aerosols by fog droplets. Nitrate was found to be the dominant inorganic species during foggy nights whereas sulfate during non-foggy nights. The aerosol neutralization ratio for fog water and interstitial aerosol samples were found to be around unity during the foggy nights which indicated that fog condensation nuclei formed upon the neutralized state of aerosol. Combined vehicular emission and road dust, biomass burning and secondary transformation were found to be main sources for the water soluble species loading of aerosol with the latter two sources were higher during foggy nights. Based on the ratio of fog water to aerosol enrichment factor, Cu, Mn and Ba found to be highly soluble. Mass scavenging efficiency (MSE) results showed that crustal oriented components scavenged rate was higher followed by the secondary components and biomass burning species. MSE for secondary species were found to be dependent directly on liquid water content and inversely on aerosol concentration. The MSE of WSOC was found to be comparable to secondary inorganics which displayed its equally important role in nucleation scavenging. The aqueous production of sulfate in the fog droplets contributed more than scavenged sulfate which can lead to enrichment in aerosol concentration after the evaporation of fog droplets.