Seasonal Physical and Chemical Features Variation of Ambient Aerosol in Lin'an

The seasonally chemical and microphysical characteristics of aerosols in Lin'an regional atmospheric pollution monitoring station is investigated. The aerosol is collected on both Teflon filters and Quartz filters at the same time which are analyzed by different methods for different purpose. The Teflon filters are prepared for analyzing the water soluble ion concentration, while the quartz filters are used for analyzing the organic carbon and element carbon. Seven sampling periods represent different seasons. The details of sampling information are listed below: from March 30, 2002 to April 8, 2002 for spring; from August 14 to 24, in 2002, from July 20 to 30, in 2003, and from August 17 to 29, in 2004 for summer; from November 7 to 23, in 2003, from November 6 to 20, in 2004 for fall, and from January 15 to February 2, 2005 for winter. The ion chromatogram analyzer is used to discuss water soluble ion concentration of aerosol. A sunset carbon analyzer is applied to measure the organic carbon and element carbon in aerosol. Not only the seasonal mass, ion and carbon concentration of ambient aerosol are studied in Lin'an, but also the size distribution characteristic of aerosol components is analyzed in detail. Generally speaking, there are obvious variations among different seasons of mass, ion and carbon concentration. For the whole size range, the mass concentration in spring is the highest with 534 μg/m³, and it is 117.21 μg/m³ in winter which is just lower than that in spring. The lowest concentration occurs in summer with 65.7 μg/m³, and 98.6 μg/m³ in fall. The ions occupy different percentage of mass in different season. In summer, the ions' concentration is 49.4% of mass concentration, and it is 11.3% in spring. At the same time, the total concentration of sulfate, ammonium and nitrate is 75%—83% of the whole ions' concentration. On the other hand, nitrate concentration varies with season greatly. The average concentration of it is only 1.7 μg/m³ in summer. The characteristic of carbon shows that the highest element carbon concentration appears in spring and the lowest appears in summer. For organic carbon, spring's concentration is the highest and winter's concentration is the lowest. Moreover, the characteristic of size distribution is also obvious. The PM₁₁ reaches 90% of the whole mass concentration. PM_2.1 also occupies 53% of the whole mass. Sulfate, ammonium and nitrate are the main ions in fine particles. The characteristic of carbon size distribution shows that the smaller the particles are, the higher the concentration reaches.