德州市采暖季环境空气含氮硫物质的污染及气-粒分配特征

Pollution of Ambient Nitrogen/Sulfur Substances and Associated Gas-Particle Distribution Characteristics during Heating Period in Dezhou City

为探究德州市采暖季环境空气中含氮/硫物质的污染特征、气-粒分配规律及影响因素,对2017年11月10日—2018年3月15日德州市市区环境空气监测站在线离子色谱分析仪监测的水溶性离子及气态前体物质量浓度的小时数据进行了分析.结果表明:①德州市环境空气监测站ρ(NO3^-)、ρ(SO4^2-)和ρ(NH4^+)平均值分别为(18.36±18.55)(12.74±10.92)(9.60±8.75)μg/m^3,在2018年1月三者均达到最高值;对比PM2.5及气态含氮/硫物质的质量浓度发现,ρ(PM2.5)和ρ(SO2)在2017年12月、2018年1月和2018年2月的月均值均较高,而ρ(SO2)与ρ(SO4^2-)、ρ(NH3)与ρ(NH4+)均在日间(08:00—17:00)出现波峰.②对颗粒态和气态含氮/硫物质质量浓度日均值进行双变量相关分析发现,ρ(SO4^2-)、ρ(NO3^-)、ρ(NH4^+)两两之间的相关系数均高于0.75,表明二次离子的形成机制相似;而ρ(NH3)、ρ(NO2)、ρ(NO)、ρ(SO2)两两之间均不存在显著相关,说明这些气态前体物来自不同的局部排放源.③过剩NH3指数(FN)平均值为0.49±0.16,说明采样时段大气处于富氨环境,过剩的NH3会与气态HNO3生成NH4NO3,因此NO3-气溶胶的形成主要受HNO3的影响或限制.④相对湿度是影响ρ(PM2.5)最重要的气象因素,高湿环境会促进二次离子的转化.研究显示,冬季采暖排放会增加环境空气中含氮/硫物质的质量浓度,气象因素(尤其是相对湿度)对含氮/硫物质的气-粒分配也有一定影响.

In order to explore the pollution and influence factors of nitrogen/sulfur substances in the ambient air during the heating period in Dezhou City,hourly data of the mass concentration of water-soluble ions and precursor gases were measured using on-line ion chromatography analyzer (IGAC,Insitu Gas and Aerosol Compositions Monitor) at an environmental air monitoring station from November 10th,2017 to March 15th,2018. The change trend of nitrogen/sulfur mass concentration in Dezhou City during the heating period was analyzed,the results were as follows: (1) The mean values of ρ (NO3^-),ρ (SO4^2-),and ρ (NH4^+) were (18. 36±18. 55), (12. 74±10. 92), (9. 60±8. 75) μg/m^3,respectively,reaching their highest values in January 2018. By comparing the mass concentration of PM2.5 and gaseous nitrogen/sulfur substances,it was found that both ρ (PM2.5) and ρ (SO2) were higher from December 2017 to February 2018,while ρ (SO2),ρ (SO4^2-),ρ (NH3) and ρ (NH4^+) peaked during the daytime (08: 00-17: 00). (2) Bi-variable correlation analysis of the daily mean values of particulate and gaseous nitrogen/sulfur substances showed that the correlation coefficients of ρ (SO4^2-),ρ (NO3^-),and ρ (NH4^+) were above 0. 75,which indicated that secondary ions undergo similar formation mechanisms. There was no significant correlation among ρ (NH3),ρ (NO2),ρ (NO) and ρ (SO2),suggesting that these precursor gases originated from different local emission sources. (3) The average value of excess NH3 index (FN) value was calculated to be 0. 49±0. 16,indicating that the atmosphere was ammonia-rich during the sampling period and the excess ammonia may form NH4NO3 when reacting with HNO3.Therefore,the formation of nitrate aerosol was mainly affected or restricted by HNO3. (4) Relative humidity was the most important meteorological factor for ρ (PM2.5),as higher humidity environmental conditions can promote the transformation of secondary ions. The research results showed that the mass concentration of nitrogen/sulfur substances in the ambient air increased with combustion emission during the winter heating period and meteorological factors,especially relative humidity,also had a measurable impact on their distribution.