Precipitation Chemistry as an Indicator of Urban Air Quality in Mersin, North-Eastern Mediterranean Region

Abstract

The chemical composition of precipitation in the city of Mersin on the Mediterranean coast of Turkey has been studied. Spatial and temporal variability of rainwater constituents have been determined from samples collected at two central and two suburban stations for the December 2003–May 2005 period. A total of 246 samples covering all precipitation events were analyzed to determine pH, conductivity, as well as major anion (Cl−, $${\text{NO}}_3^ - $$ , $${\text{SO}}_4^{2 - } $$ ); major cation (H+, Na+, K+, Ca2+, Mg2+, $${\text{NH}}_4^ + $$ ) and formaldehyde (HCHO) concentrations. The pH varied within a range of 4.8–8.5, with only 8 out of 246 samples being acidic (pH < 5.6), and the remaining highly alkaline samples being neutralized by either $${\text{NH}}_4^ + $$ in rainwater, or by CaCO3 resulting from wet deposition of atmospheric dust. The volume weighted mean ΣAnion/ΣCation ratio was 0.49. The equivalent concentration of major ionic species followed the order: $${\text{Ca}}^{2 + } > {\text{HCO}}_3^ - > {\text{SO}}_4^{2 - } > {\text{Cl}}^ - > {\text{NH}}_4^ + > {\text{Na}}^ + > {\text{Mg}}^{2 + } > {\text{NO}}_3^ - > {\text{K}}^ + > {\text{H}}^ + $$ . Formaldehyde concentrations varied in the range of 0.01–17.9 μM, and was found to be dependent on precipitation volume. Relatively higher $${\text{NH}}_4^ + $$ , $${\text{SO}}_4^{2 - } $$ , $${\text{NO}}_3^ - $$ and HCHO concentrations, mainly of anthropogenic origin, measured near the city center suggest increased pollution from local anthropogenic sources, e.g., residential heating, industrial and/or traffic emissions. In general, the results of this study suggest local precipitation chemistry is more strongly influenced by natural (mineral dust and marine) sources compared to anthropogenic ones.