降水污染的簇分析

运用簇分析区分不同时间段降水的化学变化,将单个降水事件作为变量来分析,每次降水测量的9项主要离子指定为簇分析的观察值,簇分析完成后,保留6类簇作为描述对象.根据簇中各离子浓度的高低,将各簇概括为:氢离子簇(簇1);无特征离子簇(簇2);氯离子、钠离子簇(簇3);硫酸根、铵根离子簇(簇4);钙、镁离子簇(簇5);硝酸根、钾离子簇(簇6).显然,簇1属酸性降水簇,簇3是海洋型降水簇,簇2、5为中间过渡型,簇4、6为高离子浓度簇,强酸性降水与高离子浓度降水并不属于同一类,降水的酸性与降水中的碱性组分密切相关,降水的酸度仅当NH4+、Ca2+离子浓度尤其是NH4+离子浓度较低时才表现为强酸性.由东北季风气流和锋面系统控制的降水(簇1、2、3)是污染物经较长距离迁移造成的强酸性降水,簇4、簇5、簇6的降水受局地污染源影响,所含的离子浓度较高.

Cluster analysis of precipitation contamination

Analysis was performed to identify the event-to-event variations in precipitation. Individual rain events were applied for analysis and selected as variables. Nine major ions measured in rain event were subjected as observations of cluster analysis. After performing cluster analysis, six clusters were retained as the optimal describing form. According to the concentration of ions in each cluster, above six clusters were classified as follows: hydrogen ion cluster (cluster 1), ion cluster without characteristic (cluster 2), chloridion and sodium cluster (cluster 3), sulfate and ammonium cluster (cluster 4), calcium and magnesium cluster (cluster 5) and nitrate cluster (cluster 6). Obviously, cluster 1 pertained to acid precipitation and cluster 3 was associated with marine precipitation while cluster 1 and 5 were of the transition types. Moreover, cluster 4 and 6 were clusters with high ion concentration. However, strong acid precipitation and high ion concentration precipitation couldn't come under the same type. Precipitation acidity was highly correlated with alkalescent components in rainwater. Rainfall was strongly acidic only when the concentration of ammonium and calcium ions, especially the former, was relatively low. The precipitation (cluster 1, cluster 2 and cluster 3)controlled by north flows including northeast monsoon flow and frontal system flow was strongly acidic and was caused by pollutants during long distance transportation. cluster 4, cluster 5 and cluster 6 that had a relatively high ion concentration were mainly polluted by source of close quarters.