2003年夏季临安地区大气气溶胶离子成分的尺度分布特征

THE CHARACTERISTICS OF AEROSOL IONIC SIZE DISTRIBUTIONS AT LIN'AN IN SUMMER OF 2003

文中利用2003年夏季在浙江临安大气本底污染监测站观测的资料,分析了临安的气溶胶质量浓度、离子成分的尺度分布特点及主要离子间的相互关系。初步结果显示,该期间临安气溶胶主要以粒径小于2.1μm的细粒子为主,约占总质量浓度的66%,其中粒径小于0.65μm的粒子可达总质量浓度的50%,远高于其他各级尺度段上的粒子浓度。与质量浓度分布相似,可溶性无机离子成分主要集中在粒径小于2.1μm(记为PM2.1)的细粒子中,PM2.1粒子中可溶性无机离子约占所有尺度段(包括所有5级)离子质量浓度总和的88%。其中粒径小于0.65μm的亚微米粒子中的离子质量浓度是细粒子的主要部分,占所有尺度段上离子质量浓度总和的77%。SO42-,NH4+和K+是PM2.1中决定性的离子成分。相关分析和离子平衡表明,PM2.1中SO42-与NH4+和K+有很高的相关,在粒径小于0.65μm的亚微米粒子中,非海盐硫酸盐(Nss-SO42-)主要为(NH4)2SO4,由气-粒转化产生;而在粒径为0.65~2.1μm尺度段,Nss-SO42-除(NH4)2SO4外,可能还有K2SO4,Na2SO4等存在。

During July 2003, a comprehensive field measurements on aerosol chemical, physical and radiative properties at Lin＇ an regional background monitoring station in Yangtze delta region of China were conducted by the project ＂An observational study on the continental baseline air over China＂. Only size resolved ionic characteristics of aerosols were discussed. Particles were sampled using Andersen multi-stage impactor sampler. After the sampling finished, samples were immediately shipped to the laboratory in Chinese Academy of Meteorological Science（CAMS） in Beijing for mass and chemical analysis. The mass was measured with gravimetric method using Sartorius mierobalance of 0.01 nag readability, which was installed in a temperature and humidity controlled clean room. The anions were analyzed using Dionex DX- 500, and the cations were analyzed using Hitachi 180 - 70 Atom Absoption Speetrometry（AAS）. 9 inorganic ions were anallyzed, which were： F^-,Cl^-,NO3^- ,SO4^2＋ ,NH4^＋ ,K^＋ ,Na^＋ ,Ca^2＋ ,Mg^2＋. In average, the mean mass concentration of particles summing over all size ranges （TSP） during the experiment was 69.6 μg/m^3, with the minimum of 45.2 μg/m^3 and maximum 90.8 μg/m^3, which was much lower than those obtained in the period from August to October, 1991 ,and also lower than that measured in October 1994 at the same site. The calculated PMll （〈 11 μm） mean mass concentration （standard deviation） was 64.0 （14. 9）μg/m^3 ,and PM2.1 （〈2.1 μm） was 46.2（13.2） μg/m^3, which was about half of mass of PMIO and PM2.5 measured in November 1999. The investigation of weather and the emission of aerosol and its precursors indicated that the lower concentration of aerosols during this measurement were not caused by emission change,the summer dry and hot weather in that region could be the main reason. Dry and hot weather reduced the conversion process of S02 to SO4^2- in liquid phase. Base on the size distribution of particle mass and ionic composition, which showed the high percentage of concentrations in the size range with less than 0.65 ttm, and ionic balance analysis, it could be inferred that the gas to particle process might play an important role in the aerosol formation during the experiment period. The statistics of aerosol data indicated that： The mass of aerosol with size less than 2.1 μm accounting for 66 % of total mass, in which about 50 % of the mass was the particles with size less than 0.65 μtm. Similar to the size distribution of aerosol mass, the water-soluble ions mainly concentrated on the size range of 〈 0.65 ttm, accounting for about 77 % of the sum of the analyzed ions, and the ions within the range of 〈 2.1 ttm reached 88 %. The sulfate, ammonium and potassium were the dominant ionic components in fine particles （particle size 〈 2.1 μm）. Ion balances implied that the sulfates in fine particles were mostly consisted of （NH4）2SO4, Na2SO4 and K2SO4, but in submicron particles the non-seal salt sulfate （NSS- S^4- ） was produced through gas-particle conversion process, and in the form of （NH4）2SO4.