北京市西三环地区大气中多氯联苯的污染特征和气粒分配

Pollution characteristics and distribution in gas-particle phase of polychlorinated biphenyls (PCBs) in the West Third Ring area in Beijing,China

以北京市西三环地区北京工商大学作为采样点,在2017年3—5月共采集气相、颗粒相(PM_(2.5)、PM_(10)、TSP)样品54个,对样品中28种PCBs单体进行定性定量分析,研究大气中多氯联苯(PCBs)的污染特征、在不同粒径颗粒物(PM_(2.5)、PM_(10)、TSP)中的分布规律和气粒分配行为.结果表明,北京市西三环地区大气中PCBs总浓度为144—859 pg·m^(-3),在国内外处于中等水平.其中,气相样品中PCBs浓度为131—814 pg·m^(-3),平均浓度为495 pg·m^(-3),占大气中PCBs总浓度的94.95%;颗粒相样品中PCBs浓度为12.3—48.9 pg·m^(-3),平均浓度为26.3 pg·m^(-3),占大气中PCBs总浓度的5.05%.低氯代PCBs更多地分布在气相上,高氯代PCBs更多地分布在颗粒相上.对不同粒径颗粒物(≤2.5μm、2.5—10μm、>10μm)中PCBs的分析表明,PCBs主要分布在≤2.5μm的颗粒物中.不同粒径颗粒物中所含PCBs同系物的组成比例接近,以三氯至七氯为主,占颗粒物中PCBs总含量的88%以上.用过冷饱和蒸气压P0L(Pa)和分配系数Kp来描述PCBs的气粒分配行为,lg Kp-lg P0L的斜率为-0.3653,说明北京西三环地区大气中PCBs的气粒分配未达到平衡状态,在气粒分配过程中以吸收机制为主.

Fifty four gas phase and particle phase（ PM2.5,PM10,TSP） samples were collected in Beijing Technology and Business University in the West Third Ring area in March to May,2017. The28 PCBs homologues in the samples were analysed, to study the pollution characteristics,composition in different size particles（ PM2.5,PM10 and TSP） and the gas-particle distribution behavior of PCBs. The results showed that the total concentrations of PCBs in atmosphere in the WestThird Ring area in Beijing were 144—859 pg·m^-3. It was at the medium level both at home and abroad. The concentrations of PCBs in gas phase samples were 131—814 pg·m^-3,the average concentrations were 495 pg·m^-3,which accounting for 94.95% of the total concentrations of PCBs in atmosphere. The concentrations of PCBs in particle phase samples were 12. 3—48. 9 pg·m^-3,the average concentrations were 26.3 pg·m^-3,accounting for 5.05%. The lower chlorinated PCBs were more distributed in gas phase,the higher chlorinated PCBs were more distributed in particle phase.The results of PCBs in different size particles（ ≤2.5 μm,2.5—10 μm,10 μm） showed that PCBs were mainly distributed in particles≤2.5 μm. The PCBs compositions in different size particles were similar,the main homologues were trichlorinated biphenyls to heptachlorinated biphenyls,which accounted for more than 88% of total PCBs concentrations in particles phase. The distribution of PCBs in gas and particle was described by Kpand PL^0（ Pa）. The slope of lg Kp-lg PL^0 Lwas-0. 3653,which indicated that the gas-particle distribution of PCBs in the atmosphere in the West Third Ring area of Beijing was not in equilibrium,and the dominant gas-particle distribution mechanism was absorption.