Background: The chemical composition of precipitation was assessed in 27 European countries from 2000 to 2017, offering a general point of view on the rainwater chemistry in Europe, contributing to a larger understanding of air pollution and atmospheric chemistry. Results: The volume-weighted mean concentrations (VWM) were calculated, showing the relative dominance of SO 4 2− and Cl − , explaining the acidic and slightly acidic pH values that ranged from 4.19 to 5.82 over Europe. The VWM concentrations of ionic species measured in rainwater usually followed the SO 4 2

The air quality decrease, especially in urban areas, is related to local-scale conditions and to dispersion of air pollutants (regional and long-range) as well. The main objective of this study was to decipher the seasonal variation of PM10, NO, NO2, NOx, SO2, O3, and CO over a 1-year period (2017) and the possible relationships between air pollution and meteorological variables. Furthermore, trajectory cluster analysis and concentration-weighted trajectory (CWT) methods were used to assess the trajectories and the source-receptor relationship of PM10 in the Ciuc basin Transylvania, known as the “Cold Pole” of Romania. The pollutants show lower concentrations during warmer periods, especially during summer, and significantly higher concentrations were observed on heating season in winter due to seasonal variations in energy use (biomass burning) and atmospheric stability. Subsequently, in February, the highest concentration of PM10 was 132 μg/m3, which is 4 times higher than the highest recorded monthly mean. Our results indicate a negative correlation between CO/temperature (− 0.89), NOx/temperature (− 0.84) and positive between NOx/PM10 (0.95), CO/PM10 (0.9), and NOx/CO (0.98), respectively. Dominant transport pathways were identified and the results revealed that slow-moving southerly (~ 45%) and northwesterly (~ 32%) air masses represent almost 80% and mainly regional flows were discerned. During 2017, increased PM10 levels were measured at the study site when air masses arrived mostly from northwest and southeast. The CWT and polarplot models show a strong seasonal variation and significant differences were observed between weekdays and weekends, namely highest PM10 concentrations during weekends at low wind speed (2–4 m/s).

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The aim of this study is the assessment of rainwater composition, regarding the various sources of major ions and heavy metals, taking into account the characteristic atmospheric circulations and the main air mass transport routes. Rainwater samples were analyzed for pH, electrical conductivity, major ions, and heavy metals. At all sampling sites, the most abundant anions were SO 4 2ā nd Clˉ, while the dominant cations were Ca 2+ and Mg 2+. Regarding heavy metals, the dominance of Pb and Cd was found. The contribution of soil dust from the mining activities and the dissolution of CaCO 3 , MgCO 3 , and CaSO 4 •2H 2 O in the rainwater explains the high concentrations of Ca 2+ , Mg 2+ , and SO 4 2−. The overall precipitation contamination with heavy metals at the three sampling sites was assessed by the degree of contamination, showing that Pb and Cd presents the highest risks of all heavy metals. The values of toxicity potential suggested an elevated risk for human health in case of rainwater ingestion, especially in rural areas. Spearman correlation and PCA indicated that the chemical characteristic of the rainwater is primarily controlled by sources such as agricultural activities, mixed and crustal sources, traffic, and other anthropogenic, industrial influences, mining activities, smelting operations, coal combustion, and metal production.

A study of precipitation chemistry was conducted for 11 years (01 January 2006-31 December 2016) in the Ciuc basin, Eastern Carpathians, Romania. The studied area is an enclosed basin, also called "the Carpathians cold pole." All collected samples were analyzed for major cations and anions. HCO concentrations were calculated based on the empirical relationship between pH and HCO. The multiannual arithmetic mean of pH values was found to be 6.57. The lowest and highest pH values were measured in 2009 and 2013, being 6.57% lower, respectively, 7.57% higher than the multiannual mean. Only 3.31% of the studied rainwater samples indicate acidic character. In descending order, the majority of the samples are as follows: NH >Ca >SO >Cl >HCO >NO >Na >K >Mg >NO >H. Principal component analysis (PCA) showed the NH, Ca, and Mg contribution to the neutralization process and their sources. The anthropogenic origin of SO was supported by the high non-sea-salt fraction (NSSF) (~ 91%). The results of this study suggest that rainwater chemistry is strongly influenced by local natural and anthropogenic sources (agricultural activities) rather than marine sources. The pollutants in rainwater samples were mainly derived from calcareous and dolomitic soil dust and specific local climatic conditions, long-range transport, local industry, and traffic sources.