2014年APEC期间北京及周边重点城市PM_(2.5)中水溶性离子变化特征

Variations of PM_(2.5) and its water soluble ions in Beijing and surrounding cities during the APEC in 2014

2014年11月北京APEC会议前后,采集了北京、天津、石家庄、保定、济南的PM2.5样品,并测定了其中Cl-、NO-3、SO2-4、Na+、NH+4、K+、Ca2+、Mg2+等8种水溶性离子的质量浓度.结果表明:(1)北京市在特殊减排期内水溶性离子浓度均有显著降低,2013年是该时段的1.2—5.2倍,会后为该时段的1.5—6.1倍.其中变化较大的是Ca2+,由2.58μg·m-3降至0.494μg·m-3,其次为SO2-4、NOx,说明土壤尘、硫化物及氮氧化物的控制尤为显著.(2)APEC期间整个北京及周边城市群地区,水溶性离子特征呈现了一定的区域性特征,二次离子占水溶性离子的80%以上,模拟方程计算可知,大气气溶胶中SO2-4、NO-3和NH+4是以(NH4)2SO4和NH4NO3形式共存.水溶性离子占PM2.5质量浓度的比重均较以往及会后降低,其中北京最低为37.8%.针对区域的阴阳离子平衡计算,阴阳离子较高的相关性(R=0.974)说明了区域呈现一定的整体性特征.会后NO-3/SO2-4比值下降,说明硫化物在减排期间浓度显著降低.污染减排措施在APEC期间对大气颗粒物中的水溶性离子污染的减轻起到了积极作用.

PM2. 5 samples from Beijing,Tianjin,Shijiazhuang,Baoding and Jinan were collected during the APEC in November,2014 and the mass concentrations of 8 water soluble ions were measured. Results show that the concentrations of 8 water soluble ions in the main cities of BeijingTianjin-Hebei region decreased significantly compared with those in 2013. The concentrations of water soluble ions decreased by 1. 2—5. 2 times from those in 2013. The most decreased ion is Ca2 ＋,which decreased from 2. 58 to 0. 494 μg·m- 3. This is ascribed to the control of soil dust. In addition,the concentration of SO2-4also decreased obviously,which is ascribed to the emission-reduction of SO2 and NOx. Secondly,the concentrations of 8 water soluble ions show obvious regional characteristics.Secondary inorganic species were major components of water soluble ions,and the percentage is ashigh as 80%. The calculation shows that SO2-4,NO-3and NH＋4coexist in the form of（ NH4）2SO4and NH4NO3 in atmospheric gas gel. The content of water soluble ions in PM2. 5in Beijing is 37. 78%,which is lower than those of Tianjin,Shijiazhuang,Baoding and Jinan. The ion balance between total cations and total anions in Beijing-Tianjin-Hebei region showed a correlation coefficient 0. 974,which indicates that the atmospheric environment in Beijing-Tianjin-Hebei region has regional characteristics. The NO-3/ SO2-4ratio decreased after the conference,which indicates the concentration of sulfides decreased obviously during this period. The emmsion reduction in the period of APEC played a positive role on the water soluble ion pollution in atmospheric particles.