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The paper presents results of long-term (for seven years) monitoring and analysis of the formation of rainwater acidity in Primorsky Krai, southern Russian Far East. These results reveal the variability in the concentrations of both of total dissolved solids (TDS) and individual elements. Two groups of years were distinguished in the general dataset during which the character of the atmospheric circulation played an important role in the ionic balance of the rainwater. The study area was shown to be characterized by predominantly acidic precipitation, with the pH of the water rarely exceeding 5.3 even at low concentrations of strong acid anions. In order to identify the factors that form the acidity of rainwater, the paper proposes to rank the initial dataset according to the value of fractional acidity. In the course of this separation, data blocks with a high and low degree of neutralization of the acid potential are distinguished. Within each data block, the relationships between the pH value and the concentrations of the major ions are defined. During the analysis, it was found that the mechanism of acid rain generation is determined by the mutual influence of natural and human-made sources. It was shown that compounds of dissolved organic carbon (DOC) were involved in both acidification and neutralization of rainwater. The results obtained indicate the predominance of natural rain acidification factors. However, during periods of cyclonic activity, even a slight increase in anthropogenic load leads to an increase in the acidity of atmospheric precipitation to critical values. [ABSTRACT FROM AUTHOR]