中国西南酸雨区降水化学特征研究进展

西南酸雨区为我国主要酸雨沉降区,且是全球三大喀斯特集中分布区之一.本文将该区9个地点的降雨资料进行了总结、整理和分析,数据包括pH值和主离子成分(Cl~-、SO_4~(2-)、NO_3~-、Ca~(2+)、NH_4~+、Mg~(2+)、K~+、Na~+).该地区降雨中的主要阴离子为SO_4~(2-)和NO_3~-,主要阳离子为Ca~(2+)和NH_4~+.与我国其它地区相比,其酸性离子、碱性离子和总离子浓度均普遍高于东南地区、而低于我国北方地区.西南酸雨区主要以pH值为4.5~5.6的弱酸性降雨为主,占总降雨频次的58%左右.根据酸、碱性离子的相关性、中和因子等分析结果,该区雨水中的酸性物质可能受到了碱性离子的中和作用,其中起主要中和作用的离子为Ca~(2+)和NH_4~+.将该区雨水pH值和酸、碱性离子浓度与我国其它地区进行对比研究发现,西南酸雨区降雨受到的中和作用要强于东南地区,但弱于北方地区的降雨.通过对西南酸雨区降雨中主要离子来源的分析和估算,降雨中的酸性离子SO_4~(2-)和NO_3~-主要来自于人为污染;99.7%的Ca~(2+)和84.0%的Mg~(2+)为陆源贡献,这可能与西南地区碳酸盐岩广泛分布有关.

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^-, SO₄^2-, NO₃^-, Ca²⁺, NH₄⁺, Mg²⁺, K⁺, and Na⁺). SO₄^2- and NO₃^- were the main anions, whereas Ca²⁺ and NH₄⁺ 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. Ca²⁺ and NH₄⁺ 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 Ca²⁺ and Mg²⁺ mainly originated from terrestrial sources and SO₄^2- and NO₃^- were mostly attributed to the anthropogenic activities in this area. In addition, approximately 99.7% of Ca²⁺ and 84.0% of Mg²⁺ were attributed to terrestrial sources and were closely related to the widespread distribution of carbonate rocks in the southwest of China.