Effects of the Eastern Carpathians on atmospheric circulations and precipitation chemistry from 2006 to 2016 at four monitoring stations (Eastern Carpathians, Romania)

A comprehensive study on the chemical composition of rainwater was carried out from 2006 to 2016 in four sampling locations from the Eastern Carpathians, Romania, in order to study the differences between the precipitation chemistry and atmospheric circulations of intra-mountain and extra-mountain areas. All samples were analyzed for pH, electrical conductivity and major ions. Daily precipitation data recorded during 1981-2016 was used to disseminate weather types that lead to the occurrence of high precipitation days. ERA reanalysis (Interim version) was used to build a database for the atmospheric circulation types, using multiple methods to compare if similar synoptic patterns are specific for the days with >10 mm of rain. Correlation between precipitation and elevation showed the orographic convection and the barrier effect. The average pH was 6.6 at Ciuc basin (CB), 6.8 at Giurgeu basin (GB), 6.9 at Deda-Toplița Pass (DTP) and 6.6 at Odorheiu sub mountain basin (OSB). Lowest pH values were measured at OSB. Here, 12% of the samples were observed to be acidic, compared to 3.31% at CB, 0.80% at GB and 1.70% at DTP. NH4+ was the most abundant ionic species at CB, GB and DTP; at OSB the dominance of both Ca2+ and NH4+ was observed. SO42− was the most predominant anion at all sampling sites, having the highest volume weighted mean (159 μeql−1) concentration at OSB. Neutralization factors, ionic ratios and the ammonium neutralization index showed the neutralization potential of NH4+ and Ca2+ over acidic components. Spearman correlation and Principal Component Analysis showed the sources of major ions. Significant correlation between Na+ and Mg2+ (R = 0.63) at OSB suggests the same source (marine) origin, from the long range transported sea sprays, and the lack of correlation between these cations at CB, GB and DTP confirms the blocking effect of the Carpathians Mountain chain.