上海城区二次污染物形成过程及影响因素研究

Formation of secondary species in submicron particulate matter ( PM_1) in downtown Shanghai-episodic analysis

利用气溶胶质谱仪在上海典型城区开展了对夏季亚微米颗粒物(PM_1)浓度及化学组分的实时在线观测,旨在捕捉污染过程、研究二次污染物的形成机制及影响因素.结果发现,上海城区二次污染物,包括二次有机气溶胶(SOA)、硫酸盐与硝酸盐是PM_1的主要组成,占比为82.5%,其中,SOA(28%)、硫酸盐(27%)与硝酸盐(27%)的比重相当.观测期间捕捉到了一个清洁期与两次污染的生消过程,清洁期的二次有机与无机污染物显著受到局地日间光化学转化过程的影响,污染过程根据气象条件的不同可以分为不同的阶段,包括传输期、累积期与消散期.传输期与消散期的局地光化学过程对SOA的形成有显著的促进作用,累积期SOA受到颗粒相水含量与区域传输的共同作用.污染期硝酸盐浓度显著上升,液相反应是促进污染期硝酸盐生成的重要因素,而污染期硫酸盐主要受到区域传输的影响.

This study presents the real-time high-resolution aerosol mass spectrometry measurements of submicron non-refractory particulate matter（ NRPM1） in urban Shanghai from August to September 2016 with the aim to identify the major episodes,formation mechanisms of the secondary species and factors that potentially affect their formation. Overall,secondary species were dominant in PM1 particles,including secondary organic aerosol（ SOA）,inorganic sulfate and nitrate,with each of them contributing equally to the total PM1 mass concentration. One clean period and two episodes were identified during the campaign. Secondary species in clean period were largely formed through local photochemical processes. The episodic events can be further divided into three stages,transportation,accumulation and dissipation. SOA was likely to form locally through photochemical oxidation in transportation and dissipation stages,while SOA was more affected by aerosol liquid water content（ LWC） and regional transport in accumulation period. During episodic events,inorganic nitrate significantly formed locally especially during the periods when LWC was high; yet inorganic sulfate was mainly affected by regional transport.