Investigating the impact of rain on aerosol morphology and chemical composition across size fractions in Hyderabad, India

Abstract

This study provides a detailed analysis of the effects of rain on aerosol morphology and chemical composition in Hyderabad (17.5° N, 78.6° E), a tropical urban site in southern peninsular India. It marks the first comprehensive size-segregated study in the region, analyzing aerosols of aerodynamic sizes 2.5 μm, 1.4 μm, and 0.44 μm before and after rain events, alongside rainwater ion analysis to assess scavenging effects. Multiple techniques were used, including ion chromatography, SEM-EDAX, FTIR, and UV–Vis spectroscopy. Results show a pronounced washing effect on inorganic components, while organic matter, particularly biogenic content, increased after rainfall. Despite rain, much of the organic fraction remained intact. EDAX confirmed a high carbon content and the presence of metal ions, such as Si, Al, Na, Ca, Fe, and Zn, originating from both anthropogenic and natural sources. Morphological analysis revealed diverse particle shapes;cubical, spherical, and columnar inorganic forms, along with biogenic particles resembling insect parts. UV–Vis results indicated high pre-rain transparency (∼99 %) in the visible range, which declined post-rain, highlighting aerosol removal. This study enhances understanding of aerosol-rain interactions in tropical urban atmospheres, informing air quality and climate models.