[Chemical Characteristics and Source of Acid Precipitation in Guilin]

A total of 396 rainwater samples of Guilin from 2008 to 2011 were collected and analyzed for pH, 44 of which were analyzed for major ions. The analysis of pH values showed the obvious seasonal variation of acid rain in Guilin. The pollution level of summer was lower than those in other seasons, while the pollution levels in winter and spring were the highest. The investigation of fractional acidity(AF) and neutralization factors(NF) indicated that low acid rain pollution level in 2008 was caused by alkali neutralization, especially NH₄⁺ and Ca²⁺. Studies of the origins of major ions showed that CI^- and Na⁺ were mainly from sea, Ca²⁺ was mainly from the crustal dust while K⁺, SO₄^2- and NO₃^- were mainly originated from anthropogenic source. Finally, the effect of regional transportation on acid rain of Guilin was analyzed and 3 originatons of acid-causing substance were oriented by an air trajectory clustering methodology based on hysplit-4 and a clustering algorithm including 1Jiangxi, Anhui, Hunan and Hubei, with high population densities, these regions contributed 19% air mass in spring, 26% in summer, 19% in autumn and 36% in winter due to the northeast wind; 2Pearl River Delta, with airflow from west Pacific passing before arriving Guilin, contributing 19% in spring, 33% in autumn and 36% in winter; 3Nanning, Liuzhou. All strong acid rain vapor air mass converged in southwest Guilin in spring, and arrived in Guilin passing Naning and Liuzhou. In summer, under the direct control of southwest monsoon, the vapor from Indian Ocean directly arrived in Guilin, accounting for 75%. The southwest airflow passing these cities accounted for 14% in autumn and 63% in winter.