Changes of Wet Precipitation Flux and Pollutants associated with at Chongqing Urban Station from 2008 to 2020 and Influencing Factors

Abstract

Based on the observations of the East Asian Acid Deposition Monitoring Network (EANET), combined with meteorological and socioeconomic data, the changes and influencing factors of the electrical conductivity (EC), pH, water-soluble ions (WSIs) and wet precipitation fluxes in Chongqing from 2008 to 2020 were analyzed. The results showed that the average values of pH, EC, WSIs, fluxes of sulfur, nitrate-nitrogen, and ammonium-nitrogen in Chongqing wet precipitation during observational periods were 5.33, 8.64 mS/m, 37.03 mg/L, 2 731 kg/(km²·a), 273 kg/(km²·a) and 1 748 kg/(km²·a), respectively. The concentration of WSIs in wet precipitation ranks in the order of SO₄^2–>NO₃^–>Ca²⁺>NH₄⁺>Cl^–>K⁺>Mg²⁺>Na⁺>F^–, among which ions of SO₄^2–, NO₃^–, Ca²⁺ and NH₄⁺ accounted for 45.2%, 23.9%, 13.0% and 11.7% of the total ions′ concentration, respectively. There were significant inter-annual and monthly variations in pollutants in wet precipitation. Inter-annual variations were mainly affected by pollutant source emissions, while monthly variations were primarily impacted by meteorological conditions. The probability of strong acid rain (52.37%) was relatively high from 2008 to 2014, accompanying stronger pollution. In comparison, strong acid rain occurred significantly less frequently (3.74%) during 2015-2020, and pollution in wet precipitation improved considerably. The wet precipitation in Chongqing from 2008 to 2010 was sulfuric acid type, and from 2011 to 2020, a mixture of sulfuric acid and nitric acid type. In summer, due to the increased amount of wet precipitation and better atmospheric diffusion conditions, the pollutant concentration in wet precipitation was lower with the lowest conductivity and highest pH levels. Conversely, in winter, the conductivity of wet precipitation is the highest, with the lowest pH levels. The monthly variations in the proportions of different WSI concentrations were slight. The impact of pollutant concentrations on the inter-annual variation of pollutant deposition fluxes was more significant than that of wet precipitation amounts. In contrast, the influence of wet precipitation amounts on the monthly variation of pollutant deposition fluxes was more significant than that of pollutant concentrations.