[Progress in the Studies of Precipitation Chemistry in Acid Rain Areas of Southwest China].

The precipitation data for nine sites in the acid rain area of southwest China were analyzed. The data included pH and the concentrations of major ions (Cl ^- , SO ₄ ^2- , NO ₃ ^- , Ca ²⁺ , NH ₄ ⁺ , Mg ²⁺ , K ⁺ , and Na ⁺ ). SO ₄ ^2- and NO ₃ ^- were the main anions, whereas Ca ²⁺ and NH ₄ ⁺ were the main cations in the precipitation. The concentrations of acidic ions, alkaline ions, and total ions in this area were significantly higher than those reported in southeast China, but much lower than those in northern China. About 58% of the total precipitation has a pH value ranging from 4.5 to 5.6. According to the correlation of acidic and alkaline ions as well as the results of the neutralization factor, the rainwater in this area has been neutralized. Ca ²⁺ and NH ₄ ⁺ are the dominant neutralization substances in rainwater. Comparisons of pH and the main ion components with other areas showed that rainfall neutralization in this area was stronger than that in southeast China but poorer than that in northern China. Calculation of enrichment factors for rainwater components relative to soil and seawater indicated that Ca ²⁺ and Mg ²⁺ mainly originated from terrestrial sources and SO ₄ ^2- and NO ₃ ^- were mostly attributed to the anthropogenic activities in this area. In addition, approximately 99.7% of Ca ²⁺ and 84.0% of Mg ²⁺ were attributed to terrestrial sources and were closely related to the widespread distribution of carbonate rocks in the southwest of China.