Influence of natural and urban emissions on rainwater chemistry at a southwestern Iran coastal site

The influence of pollutant sources on rainwater chemistry is investigated at an industrial coastal site in Iran (Mahshahr) where frequent dust storms occur throughout the year. For this purpose, rainwater samples from two main pluvial systems were collected and analyzed for major ions and selected heavy metals (Al, Cu, Ni, Pb and Zn). The differences in calculated and measured pH values of rainwater pointed to the important effect of neutralizing agents, specifically Ca ²⁺ , Na ⁺ and Mg ²⁺ , in offsetting the high acidity generated by NO ₃ ⁻ and SO ₄ ²⁻ to yield alkaline rainwater. A comparison of species concentration ratios relative to those for pure seawater and Earth's crust revealed that nearly all NO ₃ ⁻ and most Ca ²⁺ , SO ₄ ²⁻ and Mg ²⁺ originated from non-marine and local sources. Compared with other areas around the world, some heavy metals (particularly Zn) displayed higher concentrations in Mahshahr rainwater. Enrichment factor (EF) analysis revealed that Cu and Ni were moderately enriched, while Pb and Zn in particular (EF > 100) were highly enriched indicating that these species in rainwater stemmed from anthropogenic activities. Positive matrix factorization (PMF) modeling indicated that the four main pollutant sources impacting the regional rainwater were soil, combustion processes, marine emissions, and the local industrial sources.