Abstract:

This study analyzes the acid rain observation data from 14 cities in Liaoning province from 2021 to 2022, mapping the spatial distribution as well as the monthly and seasonal variations of precipitation pH values. It assesses that the frequency of acid precipitation and its correlation with acidic gaseous pollutants in different cities of Liaoning province. The results show that the average annual precipitation pH value across coastal areas is low. Dalian has the lowest average annual precipitation pH at 5.77, while Jinzhou has the highest at 6.74. The minimum annual pH value of 5.72 is recorded in December, the highest frequency of acid precipitation is 7.94%;while, the highest annual pH value is 6.25 in April, and the frequency of acid precipitation is 1.72%. Among the 14 cities, Anshan records the lowest occurrence of acid rain at 0.24%, while Huludao exhibits the highest frequency at 11.79%. Due to the washout effect of alkaline aerosol particles and the wet removal process during precipitation, the pH values in Liaoning province are higher in spring, decrease during summer and autumn, and reach their lowest in winter. Monthly variations of SO₂ and NO₂ concentrations in Benxi, Dandong, Dalian, and Huludao show lower levels in summer and higher levels in winter, which indicating a local emissions influence on acid precipitation in winter, while summer acid precipitation is significantly impacted by wet removal processes. Furthermore, the pH value decreases and the frequency of acid precipitation increase when precipitation is less than 50 mm. Conversely, the pH value rises and concentrates between 6 and 7 when precipitation exceeds 100 mm. Wind directions influence significantly the source and sink dynamics of key atmospheric pollutants affecting the pH value of precipitation. Dust storms driven by prevailing spring winds contribute to an increase in atmospheric alkaline aerosols, which in turn elevate precipitation pH levels. In summer, southward airflow brings in substantial moisture, leading to a rise in acid precipitation events.

Key words: pH value of precipitation, Acid rain frequency, Gaseous pollutants