Assessing the variations in the chemical composition of rainwater and air masses using the zonal and meridional index

Abstract The chemical composition of rainwater was studied from January 2009 to December 2017 in the northern group of Eastern Carpathians, Romania, taking under consideration air mass trajectories, the zonal index and zonal circulations, to show the imprints of long-range transported pollutants on the precipitation chemistry. Rainwater samples were analyzed for pH, major anions and cations. The relative dominance of ions among sampling sites was quite similar, Ca2+ and SO42− being the most abundant. Neutralization was primarily brought by Ca2+, followed by NH4+, proven by the ionic ratios, neutralization factors, neutralizing and acidic potential, and the significant correlation coefficients between the sum of alkaline species (Ca2+ + Mg2+ + NH4+) and the sum of acidic species (NO3− + SO42−). Source apportionment showed the relative contributions of marine, crustal and anthropogenic sources to the total chemical composition of rainwater, indicating the significant influence of anthropogenic activities (mining, coal combustion) but the imprints of soil derived ions and sea salts can also be observed. The cluster analysis of air mass back trajectories showed that the studied region's climate and the atmospheric chemistry may have been influenced by long-range transported pollutants originated from NW and SW part of the continent. Zonal circulations and the daily zonal index using ERA Interim were constructed, demonstrating the greater influence of air masses coming from NW and SW, highlighting the polluting sources outside the European Union.