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大气气溶胶与雾霾的有机碳来源分析

时间:2023-09-24 理论教育 版权反馈
【摘要】:从相关性来看,OC、EC的来源有明显的地区差异。在DS1期间和DS2来临前夕,OC的浓度以及OC/Al比值的变化和EC类似。但在DS2到来时及随后的几天,OC浓度的变化则和EC不同,没有出现持续下降的趋势,而且OC和Al的浓度变化也不呈线性关系,表明在DS2期间,外来传输的地壳沙尘不是OC的主要来源。OC和EC在此因子中的高载荷,进一步说明了工业和机动车尾气排放,是OC和EC的主要来源。

大气气溶胶与雾霾的有机碳来源分析

气溶胶粒子各种组分之间的相关关系,在一定程度上可反映它们的共同来源。根据不同污染源的排放特征,选取了K+、F-、Cl-、SO 2-4、As、Zn、Pb、Al,对OC、EC作了相关性分析。从相关性来看,OC、EC的来源有明显的地区差异。北京城区(北师大)的OC、EC来源较多,几乎除了地壳源不是其主要来源之外,其他污染源如燃煤、机动车尾气排放、工业、生物质燃烧,都对OC、EC有很大的贡献。密云也是如此,但密云采样点设在密云水库旁一座小山上,周围没有任何厂矿企业,机动车也很少。其OC、EC的多种来源,要归于周边地区包括北京城区的污染物传输。

选用Al作为地壳源沙尘的代表。当比值(X/Al)气溶胶/(X/Al)地壳高的时候,气溶胶主要源于污染;当该比值低,接近于地壳中的比值时,则这些污染主要来自地壳源。在DS1高峰期间,Al和EC浓度都增加,其比值(1.65)和常日相近;而沙尘暴刚过,大风将污染物清除,EC和Al浓度都降低,EC/Al也降至0.48,接近北京土壤中的EC/Al值0.33,说明DS1期间的EC,主要来源于本地污染。DS2来临前夕,EC/Al为2.3,还是处在常日范围内;到了沙尘来临,Al增加,而EC浓度开始降低,EC/Al比值降为0.51。在沙尘后的几个样品中,EC和Al的浓度都下降,但EC/Al比值比较稳定,均在0.4左右,远低于常日比值,而且EC和Al的浓度变化基本呈线性关系。在DS2期间,Al在颗粒物中的百分含量由常日的4.3%增加到7.0%,非常接近Al在地壳(6.78)和在西北沙漠沙尘中的百分含量(7.0)[26]。这些结果表明,在DS2期间,EC主要出于长距离传输而来的地壳沙尘。EC和Zn、Pb的关系与EC和Al的关系(沙尘期间的浓度变化呈线性关系,而非沙尘暴期间则呈明显的非线性关系)不同的是,无论在沙尘暴期间还是非沙尘期间,EC和Zn、Pb都呈很好的线性关系,相关系数都在0.9左右。这表明,无论沙尘还是非沙尘期间,生物质燃烧、工业排放和机动车排放,都是EC最主要的来源。OC浓度在沙尘暴期间的变化和EC有所差别。在DS1期间和DS2来临前夕,OC的浓度以及OC/Al比值的变化和EC类似。但在DS2到来时及随后的几天,OC浓度的变化则和EC不同,没有出现持续下降的趋势,而且OC和Al的浓度变化也不呈线性关系,表明在DS2期间,外来传输的地壳沙尘不是OC的主要来源。如前讨论,沙尘暴过后带来的大量沙尘,促进了二次有机气体的二次转化,使得OC浓度在沙尘过后有小幅增加。把OC、EC和所有测定的气溶胶中的元素及离子组分一起进行因子分析,结果显示,OC、EC和Zn、Pb、Ni、Cu一起,属于有高负载的同一个因子,解释了总变量的23.63%,代表了工业和汽车尾气的复合源。OC和EC在此因子中的高载荷,进一步说明了工业和机动车尾气排放,是OC和EC的主要来源。

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