太原市大气PM_(2.5)中碳质组成及变化特征

Composition and Variation Characteristics of Atmospheric Carbonaceous Species in PM_(2.5) in Taiyuan,China

采用DRI Model 2001A热/光碳分析仪测定了2009年冬季和2010年春季太原市区大气细粒子(PM2.5)中有机碳(OC)和元素碳(EC)的昼夜变化特征,分析了含碳物质的变化特征,并探讨了其来源.结果表明,PM2.5、OC、EC平均浓度水平和OC/EC平均值均呈现出冬季[(289.2±104.8)μg·m-3、(65.2±22.1)μg·m-3、(23.5±8.2)μg·m-3和2.8±0.3]高于春季[(248.6±68.6)μg·m-3、(29.7±6.2)μg·m-3、(20.2±5.4)μg·m-3和1.5±0.3],冬季夜晚[(309.3±150.0)μg·m-3、(74.6±19.5)μg·m-3、(24.3±6.6)μg·m-3和3.1±0.3]高于白天[(234.9±122.1)μg·m-3、(54.9±28.2)μg·m-3、(22.6±10.8)μg·m-3和2.5±0.5],春季白天[(292.5±120.8)μg·m-3、(32.7±10.5)μg·m-3、(22.7±10.1)μg·m-3和1.6±0.5]高于夜晚[(212.3±36.7)μg·m-3、(29.6±6.6)μg·m-3、(20.7±6.4)μg·m-3和1.5±0.2]的污染特征.这是因为冬季处于采暖期,特别是夜晚,煤和生物质燃烧量增加导致碳质颗粒物排放量增加以及大气温度低且稳定不利于污染物扩散;高的OC/EC是OC排放量增加所致而非二次有机碳(SOC)的贡献,因为气温低且太阳辐射弱不利于SOC的生成.春季白天PM2.5、OC和EC浓度水平高于夜晚可能是白天风速比夜晚大且相对湿度比夜晚低而更有利于城市扬尘形成所致,OC/EC高可能是白天温度较高且太阳辐射较强有利于SOC的生成.与国内其他城市相比,太原PM2.5、OC和EC均处于较高的浓度水平,表明太原碳质气溶胶污染严重,可能对城市灰霾形成有重要贡献.

Day-night variation characteristics of organic carbon( OC) and elemental carbon( EC) in atmospheric fine particles( PM2. 5) collected during winter of 2009 and spring of 2010 in Taiyuan city were analyzed using DRI Model 2001 A Thermal/Optical Carbon Analyzer,and the sources of carbonaceous materials in PM2. 5were analyzed. The results showed that the average concentrations of PM2. 5,OC,EC and average OC/EC ratios were all higher during winter [( 289. 2 ± 104. 8) μg·m- 3,( 65. 2 ± 22. 1) μg·m- 3,( 23. 5 ± 8. 2) μg·m- 3and 2. 8 ± 0. 3]than during spring [( 248. 6 ± 68. 6) μg·m- 3,( 29. 7 ± 6. 2) μg·m- 3,( 20. 2 ± 5. 4)μg·m- 3and 1. 5 ± 0. 3],higher in nighttime [( 309. 3 ± 150. 0) μg·m- 3,( 74. 6 ± 19. 5) μg·m- 3,( 24. 3 ± 6. 6) μg·m- 3and 3. 1± 0. 3]than in daytime [( 234. 9 ± 122. 1) μg·m- 3,( 54. 9 ± 28. 2) μg·m- 3,( 22. 6 ± 10. 8) μg·m- 3and 2. 5 ± 0. 5]during winter while higher in daytime [( 292. 5 ± 120. 8) μg·m- 3,( 32. 7 ± 10. 5) μg·m- 3,( 22. 7 ± 10. 1) μg·m- 3and 1. 6 ± 0. 5]than in nighttime [( 212. 3 ± 36. 7) μg·m- 3,( 29. 6 ± 6. 6) μg·m- 3,( 20. 7 ± 6. 4) μg·m- 3and 1. 5 ± 0. 2]during spring. This result was explained by the fact that winter is a 'heating season',especially in nighttime,emission of carbonaceous particles was increased because of the increase of coal and biomass combustion and diffusion of pollutants was difficult because of low atmospheric temperature and stable atmospheric conditions; and high OC / EC was caused by increase of OC emission but not contribution of secondary organic carbon( SOC) since low temperature and weak solar radiation were not favorable for the formation of SOC. The higher concentrations of PM2. 5,OC and EC in daytime than in nighttime during spring might be due to more dust in daytime because of higher wind speed and lower relative humidity in daytime than in nighttime,and the higher OC / EC in daytime than in nighttime might be caused by higher temperature and stronger solar radiation in daytime,which were favorable for the formation of SOC. Comparing with other cities in China,Taiyuan showed high concentrations of PM2. 5,OC and EC,indicating serious carbonaceous aerosol pollution which may significantly contribute to the formation of dust-haze.