| Summary: | To achieve a holistic understanding of the intricate interactions among human activities, atmospheric chemistry, and acid rain in China, a rigorous analysis of rainwater chemistry was made using a dataset comprising 2656 data points from 24 sites. The main cation and anion in the chemical composition of precipitation were Ca<sup>2+</sup> and SO<sub>4</sub><sup>2−</sup> in China, with an average concentration of 169.9 μeq/L and 135.4 μeq/L, respectively. Acid rain generally occurs in southern cities such as Shenzhen, Guangzhou, Zhuhai, Xiamen, and Chongqing. There were evident regional disparities in acidity and ion concentrations in rainwater, with an increase in acidity and a decrease in ion concentrations from north to south across China. Utilizing positive matrix factorization, the study found that NH<sub>4</sub><sup>+</sup>, SO<sub>4</sub><sup>2−</sup>, and NO<sub>3</sub><sup>−</sup> mainly originated from anthropogenic sources such as fossil fuel combustion, vehicle exhaust emissions, agricultural fertilization, and industrial emissions (as reflected by F3 and F4). Ca<sup>2+</sup> mainly stems from crustal factors, including industrial dust and natural crust (as represented by F1 and F4). Na<sup>+</sup> and Cl<sup>−</sup> were traceable from marine sources (as reflected by F5), while Mg<sup>2+</sup> originated from crust origin (as presented by F1). K<sup>+</sup> was mainly derived from a mixed source of crust, marine, and biomass burning (as indicated by F2 and F3). The correlation analyses showed that SO<sub>4</sub><sup>2−</sup> and NO<sub>3</sub><sup>−</sup> showed significant correlations with GDP and population. F<sup>−</sup> was associated with wastewater, which may be linked to the production of brick and tiles from clay with high fluoride contents. The pH was negatively related to industrial wastewater. Long-term analysis of precipitation chemistry in four cities suggested a clear decrease in the proportion of SO<sub>4</sub><sup>2−</sup> but a considerable increase in the proportion of NO<sub>3</sub><sup>−</sup> in anions in metropolitans of Shanghai and Chongqing due to the environmental measures that targeted reducing sulfur dioxide (SO<sub>2</sub>) emissions and increase of vehicles. This showed that pollution control strategies had an impact on precipitation ion concentrations. These results can conclude that economic and industrial growth, which will increase energy consumption, utilization of coal combustion, and a subsequent rise in pollutant emissions, can contribute to the change in the chemical compositions of rainwater and the exacerbation of acid rain.
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