华南沿海城市PM2.5污染特征及来源解析

基于2017年12月25日至2018年1月16日1 h时间分辨率的在线监测数据,对华南沿海城市——阳江市的大气PM_2.5质量浓度、化学组分和来源进行了分析.结果表明,采样时段阳江市PM_2.5中主要化学组分为OM、NO^-₃、SO^2-₄、NH⁺₄和EC,质量浓度占比分别为32.75%、25.59%、16.41%、12.37%和4.82%.相比清洁过程,两次污染过程期间NO^-₃质量浓度均为清洁过程时段的6倍以上,增量明显高于其他组分,占比则均为清洁过程时段的2倍以上,分别占29.38%和30.81%.PMF解析结果表明,二次转化源是最主要的源,其分担率高达51.41%,其中NO_x二次转化源分担27.18%,是阳江市PM_2.5分担率最大的二次转化源.首要的一次排放源是机动车源(15.11%).污染过程期间NO_x二次转化源的分担率显著提升,从11.85%分别增至33.15%和36.96%,是阳江市大气PM_2.5污染形成的主要原因.本研究表明阳江市冬季PM_2.5污染特征已类似于大型和特大城市,即面临严峻的二次污染,应着重加强对硝酸盐的防治,同时注重机动车管控.

Characteristics and source apportionment of PM2.5 in a South China coastal city

Based on the online measurements from December 25,2017 to January 16,2018,we investigated the chemical composition and sources of PM_2.5 in Yangjiang,a South China coastal city.PM_2.5 in Yangjiang mainly consisted of OM,NO^-₃,SO^2-₄,NH⁺₄ and EC,with proportions of 32.75%,25.59%,16.41%,12.37% and 4.82% in mass fraction,respectively.In two pollution events,the mass concentration of NO^-₃ increased to over 6 times of that during clean period,much higher than the increments of other components.The mass fractions of NO^-₃ in two polluted events increased to 29.38% and 30.81%,over twice of that in clean period.Source apportionment of PM_2.5 were performed by Positive Matrix Factorization,which pointed out that secondary formation was the main source/process (51.41%) for PM_2.5 in winter in Yangjiang.The secondary formation from NO_x,contributing 27.18% to the total PM_2.5 mass concentration,was the dominating secondary source.Vehicle exhausts were the biggest primary source (15.11%).In the pollution events,the contribution of the secondary formation from NO_x sharply increased from 11.85% to 33.15% and 36.96%,which should be considered as the dominating source of PM_2.5 pollution in winter of Yangjiang.This study revealed that,as a coastal city,Yangjiang exhibited similar characteristics to those big cities and mega-cities in terms of the PM_2.5 sources,i.e.,dominated by the secondary formation.It suggested that more effort for pollution control should be put into the reduction of nitrates as well as their precursor NO_x,meanwhile a persistent control of vehicles in Yangjiang city is recommended.