珠海2019年秋季一次大气污染过程的特征、成因及来源分析

Analysis of the characteristics, formation mechanisms and sources of an atmospheric pollution in Zhuhai during the autumn of 2019

2019年秋季在珠三角典型沿海城市珠海观测到一次中重度污染过程,本文对此次过程的污染特征、形成机制和来源进行了研究.通过采集PM_(2.5)样品,分析了9种水溶性无机离子(WSIIs)、有机碳(OC)、元素碳(EC)和水溶性有机碳(WSOC)等化学组分的浓度水平和污染特征;进一步结合污染过程中的不利天气形势、72 h后向气流轨迹及PM_(2.5)的潜在源贡献因子(WPSCF)和浓度权重轨迹(WCWT)等方法分析了污染的形成机制和来源.结果表明,有机物(OM)是污染时期PM_(2.5)中增长最快的组分,其次是占WSIIs约82.46%的SO_(4)^(2-)、NO_(3)^(-)和NH_(4)+(SNA).NO_(3)^(-)/SO_(4)^(2-)均值为0.20,表明珠海以固定源污染为主;硫氧化率(SOR)均值为0.65,氮氧化率(NOR)均值为0.08,高温高湿的气象条件可能是造成珠海比中国其他城市SOR偏高而NOR偏低的原因.在污染时段,二次有机碳(SOC)明显增加,WSOC/SOC随污染物的升高而降低并趋近于1,因此,污染时期的WSOC可能主要是二次生成的.副高控制型、台风外围型和高压出海型等天气形势控制着整个珠三角地区时,不利于污染物的传输和扩散,使污染加剧.后向气流轨迹分析表明,污染时期的气团轨迹主要来自于高污染的内陆地区,这可能是造成此次污染形成的重要原因和来源.WPSCF和WCWT的高值区主要集中在江西、广东等内陆地区,因此,珠海在控制本地排放的同时,也应该关注上风向临近省市的污染排放.

The characteristics,formation mechanisms and sources of secondary pollutants were investigated in a medium-to-heavy pollution process in Zhuhai,a typical coastal city in the Pearl River Delta region(PRD)during the autumn of 2019.In this paper,the concentration levels and pollution characteristics of nine water-soluble inorganic ions(WSIIs),organic carbon(OC),elemental carbon(EC)and water-soluble organic carbon(WSOC)were analyzed.We used weather situations,72 h backward trajectories,weighted potential source contribution factor(WPSCF)and weighted concentration weight trajectory(WCWT)to identify the formation mechanisms and sources.Organic matter(OM)increased most rapidly during the polluted period,followed by SO_(4)^(2-),NO_(3)^(-)and NH_(4)^(+)(SNA),which accounted for about 82.46%of WSIIs.The average value of NO_(3)^(-)/SO_(4)^(2-)was 0.2,demonstrating that the main source of water-soluble ions was from stationary emissions.The mean values of sulfur oxidation ratio(SOR)and nitrogen oxidation ratio(NOR)were 0.65 and 0.08,respectively.Meteorological conditions of high temperature and high humidity may lead to high SOR and low NOR by comparing with other cities.With increasing secondary organic carbon(SOC),WSOC/SOC decreased to 1,which suggests the WSOC may be mainly from secondary formation in the polluted period.Adverse weather conditions such as typhoon periphery,high pressure moving to sea and subtropical high controlled the whole Pearl River Delta.Therefore,the stable weather situation was unfavorable for the transport and diffusion of air pollutants.The air mass trajectories from the highly polluted inland area during the polluted period may be the main causes and sources of the pollution.Besides,the large values of WPSCF and WCWT were mainly located in the inland areas such as Jiangxi and Guangdong Provinces.Therefore,in Zhuhai,the focuses should be not only on local emission control but also on the pollution emissions from upwind neighboring cities and provinces.