Chemical Characteristics of Precipitation in Huairou District, Beijing in 2019

To reveal the current status of acid rain pollution and the chemical composition of precipitation in Huairou District, Beijing, the precipitation data from Huairou District in 2019 were used to analyze the pH value and chemical components of precipitation. The results show that: 1) In 2019, the average pH value of precipitation in Huairou District was 5.85, with 4 occurrences of weakly acidic precipitation, which accounted for 9.1% of the total precipitation events. The pH value was highest in spring, followed successively by winter, summer and autumn. The average annual electrical conductivity of precipitation was 39.8 μS/cm, with the value below 50 μS/cm from July to September. 2) The key chemical components in precipitation were Ca²⁺, NH₄⁺, Mg²⁺, SO₄^2－, NO₃^－, and Cl^－, among which the alkaline ions with strong acid-neutralizing capacity, namely Ca²⁺, Mg²⁺, and NH₄⁺, accounted for 30.0%, 11.9%, and 58.1% of the neutralization effect, respectively. The average equivalent concentration ratio of SO₄^2－/NO₃^－ was 5.0, indicating that the precipitation was of the sulfate type or coal combustion type. The average value of Cl^－/Na⁺ was 3.81, suggesting that in addition to being transported from the ocean, Cl^－ and Na⁺ were also affected by anthropogenic activities. Ca²⁺ and Mg²⁺ were mainly influenced by external sources such as dust storms. High winds were responsible for the high concentration of NH₄⁺ in spring. The concentration correlation coefficients between NH₄⁺ and SO₄^2－ or NO₃^－ were higher than those between Ca²⁺ and SO₄^2－or NO₃^－, indicating that the neutralization effect of the alkaline cation NH₄⁺ on the acidifying anions SO₄^2－ and NO₃^－ was greater than that of Ca²⁺.