On the chemical nature of precipitation in a populated Middle Eastern Region (Ahvaz, Iran) with diverse sources

This study reports on the chemical composition of rainwater collected at three ground sites with varying degrees of pollution in Ahvaz, Iran, between January 2014 and February 2015. A total of 24 rainwater samples were analyzed for pH and concentrations of trace elements (Fe, Al, Pb, and Cd) and major ions (Na⁺, NH₄ ⁺, Ca²⁺, Mg²⁺, HCO₃ ⁻, NO₃ ^–, Cl^– and SO₄ ²⁻). Principle Component Analysis (PCA) was used to identify sources of the measured species. The equivalent concentration of the components followed the order of Ca²⁺ > SO₄ ²⁻ > HCO₃ ⁻ > NH₄ ⁺ > Cl^– > Na⁺ > NO₃ ⁻ > Mg²⁺. The average pH of the rainwater samples was 6, and only three events exhibited acidic conditions below a pH of 5.6. The lowest and the highest average pH values were observed in the high traffic area (5.96) and industrial area (6.54), respectively. The highest and lowest Ca²⁺ levels were observed in the industrial and high traffic areas, respectively. Na⁺, Mg²⁺, and SO₄ ²⁻ exhibited their highest and lowest concentrations in the industrial and high traffic areas, respectively. 70.36% of the total variance was due to anthropogenic species (Ca²⁺, SO₄ ²⁻, Mg²⁺, NO₃ ⁻, Cl⁻), soil particles (Cl⁻, Na⁺, and HCO₃ ⁻), and biomass burning (NH₄ ⁺, pH). The results of this study show that local anthropogenic sources and Middle Eastern Dust (MED) storms affect the rainwater chemistry strongly, which the latter stems from the Arabian Peninsula, Kuwait, Iraq, and some parts of Iran.