中部城市秋冬季PM_(2.5)水溶性离子的化学特征及来源

Chemical characteristics and sources of PM_(2.5) and water-soluble ions in autumn and winter in central China

PM_(2.5)是影响空气质量、引发灰霾污染发生的关键污染物.本研究以南昌为主要采样对象,分析了南昌市2017—1018年秋、冬季PM_(2.5)和水溶性无机离子(WSIIs)的化学组成及其来源,并同时期采样和对比分析了中部城市(武汉和长沙)秋冬季(10月和1月)PM_(2.5)及WSIIs化学特征及其来源.结果表明,南昌市采样期间WSIIs平均占PM_(2.5)质量浓度的60%以上,PM_(2.5)和WSIIs组成在秋、冬季差别明显,在秋季,PM_(2.5)为(22.5±9.1)μg·m^(-3),空气质量较清洁,以SO_(4)^(2-)为WSIIs中最高含量的组成离子;NO_(3)^(-)的氧同位素(δ;0)值为+72.2‰±5.5‰,贝叶斯同位素混合模型表明NO_(3)^(-)以OH氧化为主要生成路径(占比54%,N_(2)O_(5)水解路径占比46%);以SO_(4)^(2-)和过量的NH_(4)^(+)作比较表明秋季一般亏损NH_(4)^(+).而在冬季,PM_(2.5)和WSIIs浓度水平比秋季有较大提高,分别为(57.6±20.9)μg·m^(-3)和(47.2±16.2)μg·m^(-3),冬季以NO_(3)^(-)为WSIIs的最高含量组成离子,δ^(18)O-NO_(3)^(-)值明显提高为+86.1%±5.1‰,NO_(3)^(-)以N_(2)O_(5)水解为主要生成路径(占比为75%);SO_(4)^(2-)和过量的NH_(4)^(+)作比较表明富NH_(4)^(+),冬季NO_(3)^(-)的快速增长和NH_(4)^(+)富余是PM_(2.5)浓度增加的重要驱动因素.基于PMF和后向轨迹分析,气团在中部城市的环流是三大城市PM_(2.5)和SNA共同污染的重要因素,说明中部城市的大气污染区域效应明显,尤其是在冬季.南昌秋季PM_(2.5)主要由二次源和扬尘贡献(共占78%),冬季主要由二次源和工业贡献(共占69%).武汉和长沙PM_(2.5)秋冬季都以二次源和工业贡献为主.

PM_(2.5)is the main pollutant of air quality,and haze weather often occurs in autumn and winter.Water-soluble ions are the main components accounting for more than 60%of PM_(2.5).In this study,the chemical characteristics and sources of PM_(2.5)and water-soluble ions(WSIIs)in autumn and winter during 2017—2018 were compared and analyzed using a variety of chemical and statistical methods during Nanchang,Wuhan and Changsha cities.The results showed that the composition of PM_(2.5)and WSIIs in Nanchang was significantly different in autumn and winter.The air was cleaner in autumn,with SO_(4)^(2-) as the primary ion of WSIIs,and the mean value ofδ^(18)O-NO_(3)^(-) was+72.2‰±5.5‰.Based on bayesian isotope mixing model,the main formation path of NO_(3)^(-)was OH oxidation accounting for 54%,and compared SO_(4)^(2-) and excess NH_(4)^(+),NH_(4)^(+)was poor in autumn.In winter,PM_(2.5)and WSIIs were(57.6±20.9)μg·m^(-3) and(47.2±16.2)μg·m·;respectively.NO_(3)^(-) was the primary ion of WSIIs,and the mean value of δ^(18)O-NO_(3)^(-) was+86.1‰±5.1‰.NO_(3)^(-) was mainly generated by the hydrolysis of N_(2)O_(5),which accounted for 75%,and NH_(4)^(+) was excess.The rapid increase of NO_(3)^(-) and excess NH_(4)^(+) are the driving factors for the increase of PM_(2.5) concentration in winter.The concentrations of SO_(4)^(2-) in autumn and winter are mainly controlled by SO_(4)^(2-) and SOR,while the concentrations of NO_(3)^(-) are not only controlled by NO_(3)^(-),NOR and formation pathway,but also influenced by temperature.Based on PMF and backward trajectory analysis,the circulation of air mass in the central cities is an important factor for the co-pollution of PM_(2.5) and SNA in the three cities,which also indicates that the regional effect of air pollution in the central cities is obvious,especially in winter.In autumn,the PM_(2.5) in Nanchang was mainly contributed by biomass combustion and dust(78%),and in winter,it was mainly contributed by industrial and vehicle exhaust(69%).In Wuhan and Changsha,the main contribution of PM_(2.5) in autumn and winter was from industrial and vehicle exhaust.