On the chemical nature of wet deposition over a major desiccated lake: Case study for Lake Urmia basin

One of the largest hyper-saline lakes in the world is Lake Urmia, which is in the northwest region of Iran. Lake Urmia has experienced extreme desiccation in recent years. This study was conducted to investigate possible impacts of aerosol emitted by Lake Urmia on rainwater properties. Rainwater samples were collected from September 2017 to September 2018 at 13 sites spanning different areas of the Lake Urmia basin. Samples were analysed for acidity/alkalinity (pH), electrical conductivity (EC), total suspended solids (TSS) and elemental composition (Na, Mg, K, Ca, Al, Fe, Ti, V, Cr, Mn, Co, Ni, Cu, Zn, As, Se, and Pb). The results reveal that rainwater around Lake Urmia is characterized by high concentrations of heavy metals and toxic elements (e.g., Fe, Al, Ni, Cu, Cr, Co, Ti), especially in the outer ring of the study region to the north. Chemical signatures of anthropogenic pollution were most evident at sites near populated and manufacturing centers. The average pH of rainwater was enhanced relative to other regions, with the lowest and highest values of the 13 sites being 7.7 and 8.6, respectively. Concentrations of marine elements (Na⁺, K⁺, Mg²⁺, Ca²⁺) decreased with increasing distance from Lake Urmia, suggestive of possible impacts of the lakebed's emission on rain composition via likely below-cloud scavenging. The area impacted by the marine aerosol emitted by Lake Urmia has a diameter of 30 to 40 km surrounding the shoreline. The results reveal a stronger signature of crustal species in the north owing to desiccated lakebed hotspots located in the north.