CHEMICAL CHARACTERISTICS OF PRECIPITATION IN REGIONAL AIR POLLUTION BACKGROUND STATIONS OF CHINA

Investigation was conducted on the chemical characteristics of precipitation in three WMO regional atmospheric background stations, the representatives of three different background features; Longfengshan (Wuchang County, Heilongjiang Province), Shangdianzi (Gubeikou village, Miyun county, Beijing) and Lin'an (Lin'an County, Zhejiang Province) background stations. The pH value and the contents of ions, SO₄^2-, NO₃^-, Cl^-, F^-, NO₃^-, Cl^-, F^-, NH₄⁺, K⁺, Na⁺, Ca²⁺ and Mg²⁺ in the precipitation were analyzed. The results show that the pH values and concentrations of SO₄^2-, NO^3-, NH₄⁺ and Ca²⁺ have obvious annual and inter-annual variation features. The variation trends are different for the three stations and between various elements. However, the concentrations of ions Cl^-, F^-, K⁺, Na⁺, and Mg²⁺ are quite low, and their variations are negligible. As for the multi-year average, the pH value for Lin'an is the lowest at the three stations, but the SO₄^2- concentration is the highest; while all values at Shangdianzi are the highest, except SO₄^2- concentration is in the middle; and all ion concentrations for Longfengshan are the lowest, except Ca²⁺ and Mg²⁺ concentrations are slightly higher than those for Lin'an, and the pH value is in the middle. The precipitation chemical features of these background stations show that the precipitation is acid at all the three stations. The worst is at Lin'an, better at Longfengshan and the slightest at Shangdianzi. It indicates that the air quality for all these three air pollution background stations is becoming worse.