天津市典型城区大气碳质颗粒物的粒径分布特征和来源

为分析天津市典型城区大气碳质颗粒物的粒径分布及其来源,于2009年12月—2010年11月采用9级惯性撞击式分级采样器对大气颗粒物进行采样,采用热光碳分析仪分析了颗粒物中的EC(元素碳)和OC(有机碳)的质量浓度. 结果表明:天津市典型城区大气颗粒物中EC和OC主要存在于细颗粒物中,在≤2.1μm的4个细粒径段中,ρ(EC)的加和年均值为(2.6±0.9)μg/m3,占PM₉(空气动力学直径≤9.0μm)ρ(TEC)的72%；ρ(OC)为(21.5±7.7)μg/m3,占PM₉中ρ(TOC)的60%. ρ(EC)和ρ(OC)季节变化显著,在≤2.1μm粒径段中,春、夏、秋、冬季的ρ(EC)分别为(1.7±0.3)、(2.1±0.4)、(3.1±0.5)和(3.7±0.5)μg/m3；ρ(OC)分别为(17.6±0.4)、(14.4±1.1)、(21.9±1.8)和(32.1±2.5)μg/m3. ρ(EC)峰值分别出现在≤0.43、>0.65~1.1和>4.7~5.8μm 3个粒径段,其中最高值出现在≤0.43μm粒径段；ρ(OC)峰值分别出现在>0.65~1.1和>4.7~5.8μm 2个粒径段,最高值出现在>0.65~1.1μm粒径段. 天津市典型城区细颗粒物中的OC、EC主要来自燃煤、机动车和烹饪排放,粗颗粒物中的OC、EC则更多来自于路面和建筑扬尘. 

Size Distribution Characteristics and Sources of Carbonaceous Aerosols in Typical Tianjin City, China

To understand the mass size distribution characteristics and its sources of carbonaceous aerosol, the particle samples were collected by an Andersen cascade impactor in Tianjin City from 2009to 2010. Organic carbon (OC) and elemental carbon (EC) in atmospheric particles were analyzed with the DRI carbon analyzer. The results showed that both EC and OC were mainly enriched in fine particles (≤2.1μm), the annual mass concentration of EC and OC in PM2.1 were (2.6±0.9) and (21.5±7.7)μg/m3with proportions accounting for 72% and 60% of PM₉, respectively. Significant seasonal differences were found during the sampling period. The seasonal average concentration of EC in spring, summer, autumn, and winter were (1.7±0.3), (2.1±0.4), (3.1±0.5) and (3.7±0.5)μg/m3, while it were (17.6±0.4), (14.4±1.1), (21.9±1.8) and (32.1±2.5)μg/m3for OC respectively during the four seasons. Log-normal size distribution of EC showed a tri-modal with peaks appeared in sizes of ≤0.43, >0.65-1.1and >4.7-5.8μm, the highest concentration was exited in size of ≤0.43μm. OC showed a bi-modal size distribution with peaks appeared in sizes of >0.65-1.1and >4.7-5.8μm, with the highest concentration usually exited in the size of >0.65-1.1μm. Ratios of OC and EC indicated that the main origins of carbonaceous aerosols in fine particles were attributed to automobile exhaust fumes, coal combustion and cooking combustion emissions, while the road dust and the coal combustion were the main sources of coarse particles.