Variation characteristics of acid rain in Zhuzhou, Central China over the period 2011-2020

Abstract

Zhuzhou was one of the most polluted cities in China with the serious acid rain. Due to the implementation of air pollution control measures from 2016 to 2018, the acid rain pollution in this city has reduced. In order to understand the recent situation, a comprehensive study on the acid rain was carried out from January 2011 to December 2020. The pH values during the study period varied from 3.3 to 7.5, with a volume-weighted mean value of 4.7. The predominant acidic components of the precipitation were SO₄²⁻ and NO₃⁻, accounting for 89.3% of the total anions. The ratio of non-sea-salt SO₄²⁻ to NO₃⁻ showed a decreasing trend, revealing that the pollution type of acid rain changed from sulfuric acid type to sulfuric acid and nitric acid compound type. The correlation analysis (p < 0.05) showed that SO₄²⁻ was positively correlated with NH₄⁺, Ca²⁺, and Mg²⁺; hence, it predominated in precipitation as (NH₄)₂SO₄, NH₄HSO₄, CaSO₄, and MgSO₄. Significant positive correlation of Ca²⁺ with Mg²⁺ shows that they may originated mainly from crust. Significant positive correlation between SO₄²⁻ and F⁻ and Cl⁻ indicate that their source may be related to the non-ferrous metal smelting industry in Zhuzhou. Further correlation analysis shows that emissions from the non-ferrous metal smelting industry in the area have a large significant on SO₄²⁻ and F⁻ in precipitation, while Cl⁻ may still be emitted from other anthropogenic sources.