Trace metal composition of rainwater and aerosol from Kolkata, a megacity in eastern India

India is one of the world's wettest countries receiving over 1000 mm of rainfall annually and also one of the countries experiencing regular floods and droughts. This study quantifies elemental composition of rainwater and aerosol collected simultaneously during 2019 monsoon season from Kolkata, a megacity in Eastern India marred by air pollution to understand sources and estimate wet deposition flux. Elemental composition (Na, Ca, Mg, Al, Fe, Mn, V, Cr, Ni, Cu, Zn, Cd, Pb) of rainwater was measured in ICP MS along with pH, conductivity, chloride (Cl−), nitrate (NO3−) and sulphate (SO42−) ions. Trace metal composition of PM10 collected in between rain events were also analysed to understand anthropogenic sources and atmospheric leaching of metals. Crustal enrichment factors (EFs) identified anthropogenic sources for Ni, Cu, Zn, Pb and Cd in PM10. Principal component analysis (PCA) identified three anthropogenic sources, industrial emission, traffic emission and waste incineration in addition to the natural background from the crustal dust for the aerosol metals. Majority of rainwater samples had almost neutral pH (average 6.81 ± 0.74, 1SD), with a range of 5.4 to 8.0. In rainwater, Na and Cl− had marine origin and majority of SO42− had non-marine sources. Cu, Zn, Cd, V, Cr and Pb concentrations of rainwater follow the trend in PM10 most likely because part of the metals are derived from aerosol leaching. The EFs indicated that all the metals except Fe had anthropogenic origin in rainwater. The wet deposition fluxes were in the order of Ca > Na > Mg > Al > Zn > Fe > Mn > Cu > Ni > Pb > Cr > V > Cd. Overall, the results show significant influence of anthropogenic sources on rainwater chemistry in addition to natural soil dust and marine aerosols. In spite of anthropogenic influence, the trace metal and anion concentrations in rainwater are well within the limits prescribed by World Health Organization (WHO), European Union (EU), USA and Indian Drinking Water Standards.