根据亚微米颗粒物PM 1中各种组分的理化特征及其对光学特性的影响,所有化学组分大体可分为以下4大类:水溶性无机离子(total water soluble inorganic ion,TWSII);有机物(organic matter,OM);矿物气溶胶(mineral);黑碳(BC)。其中的TWSII总浓度是实际测定的十多种无机离子浓度的总和,有机物浓度是实际测定的OC浓度乘上系数1.8,BC是实际测定的浓度。颗粒物中的矿物气溶胶浓度是根据实际测定的相关元素浓度,再根据公式[矿物气溶胶浓度]=2.2[Al]+2.49[Si]+1.63[Ca]+2.42[Fe]+1.94[Ti][27]估算而来,其中Si浓度是根据实际测定的Al浓度,再根据Si和Al在地壳中的比值(Si/Al=3.43)估算而来。图38-3显示了上述四大类组分在各个季节占大气气溶胶PM 1总质量的相对比值。
图38-3 PM 1中各组分在颗粒物中的比例(彩图见下载文件包,网址见14页脚注)
由图38-3可以清楚地看到,在4个季节,亚微米颗粒物PM 1中的TWSII和OM,合计占PM 1总质量的比例高达75%~80%,说明了人为污染源是亚微米颗粒物PM 1的最主要贡献者。颗粒物中的水溶性离子和OM,大都来自人为污染源。根据上述有关章节的讨论,上海PM 1主要来源于机动车排放与工业排放,而近年来机动车排放对上海亚微米颗粒物PM 1的贡献越来越大。矿物气溶胶在颗粒物中的比例在4个季度间变化不大。在沙尘暴活动较弱的年份,外来沙尘不是矿物气溶胶的主要来源,而扬尘,包括建筑扬尘、街道扬尘、机动车带起的扬尘,将原来沉降的矿物气溶胶再次带到大气中。这部分经过沉降再扬起的矿物气溶胶,比沙尘源区的沙尘气溶胶更多地富集在细颗粒物中。这也是为什么矿物气溶胶在上海雾霾及重度雾霾过程中的浓度也上升的原因。
综上所述,上海大气亚微米颗粒物PM 1,是上海颗粒物污染的核心贡献者,也是形成上海雾霾的占压倒比例的颗粒物粒径范围。换句话说,上海的大气污染问题,主要是细颗粒物乃至亚微米颗粒物PM 1的污染问题。OM和可溶性无机离子是上海大气亚微米颗粒物PM 1的最主要组分。二次无机离子SO 2-4、NO-3、NH+4(SNA)三离子及其形成的具高度吸湿性的化合物(NH 4)2 SO4和NH 4 NO 3,是上海大气亚微米颗粒物PM 1的最重要组分,在冬季NH 4 NO3比(NH 4)2 SO4浓度上升更快。船舶排放已经是上海大气不可忽视的污染源。
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【注释】
[1]“同步手工膜采样”表示人工使用滤膜采样器采样,并和气溶胶在线监测仪同步采样。也可称为“同步人工膜采样”。
[2]当量比定律亦称当量定律:当两种物质完全作用时,它们的克当量数相等。
[3]KMO(Kaiser-Meyer-Olkin)检验统计量是用于比较变量间简单相关系数和偏相关系数的指标,主要应用于多元统计的因子分析。KMO统计量是取值在0和1之间。当所有变量间的简单相关系数平方和远远大于偏相关系数平方和时,KMO值越接近于1,意味着变量间的相关性越强,原有变量越适合作因子分析;当所有变量间的简单相关系数平方和接近0时,KMO值越接近于0,意味着变量间的相关性越弱,原有变量越不适合作因子分析。
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