重庆三大城区夏季PM_(2.5)中有机碳和元素碳的污染特征

以重庆市渝北区、南岸区和渝中区3个主要城区为研究对象,采集夏季PM2.5样品,应用DRI Model 2001A热/光分析仪,采用IMPROVE-TOR方法测定了PM2.5中有机碳(OC)和元素碳(EC)含量,并对3地的OC、EC污染特征进行了评价,探讨了PM2.5中含碳物质的来源。结果表明,南岸区OC、EC质量浓度分别为(5.8±1.5)、(2.5±0.8)μg·m-3,低于渝北区((8.9±3.2)、(4.2±1.6)μg·m-3))和渝中区((8.8±2.2)、(4.6±1.3)μg·m-3),与PM2.5质量浓度的分布一致,表明渝北区和渝中区的含碳污染物的排放可能较为严重。渝北区、南岸区和渝中区的OC与EC均显著正相关,表明三大城区OC和EC可能分别具有相似的一次污染源。排除降雨天和O3浓度较高的晴天,利用m(OC)/m(EC)比值法对渝北区、南岸区、渝中区二次有机碳(SOC)进行估算,SOC质量浓度分别为(2.0±1.8)、(1.0±0.7)、(2.3±2.0)μg·m-3,占OC比例均低于30%。渝中区SOC对OC的贡献率最高,这可能是因为该地区易于形成城市热岛效应,且热量和辐射效应更加明显,有助于SOC的生成。通过计算PM2.5中8个碳组分丰度,初步判断机动车尾气排放可能是三大城区碳质组分的主要来源。

Characterization of organic carbon and elemental carbon in PM2.5 during summer in Chongqing,China

PM_2.5 samples were collected at three sites located in Yubei, Nan'an and Yuzhong in Chongqing during the summer of 2014. The concentrations of organic carbon (OC) and elemental carbon (EC) were analyzed with a DRI model 2001A thermal optical carbon analyzer using the IMPROVE-TOR protocol. The pollution characteristics of OC and EC at these sites were evaluated, and the sources of carbonaceous materials in PM_2.5 were investigated. The average concentrations of OC and EC were (5.8±1.5) and (2.5±0.8) μg·m^-3 in Nan'an, lower than those in Yubei ((8.9±3.2) and (4.2±1.6) μg·m^-3) and Yuzhong ((8.8±2.2) and (4.6±1.3) μg·m^-3). This is consistent with the concentration distribution of PM_2.5, suggesting that the emissions of carbon may be more serious in Yubei and Yuzhong. Concentrations of OC and EC in PM_2.5 were found to be significantly correlated in Yubei, Nan'an and Yuzhong, suggesting that they may have similar primary sources. For Yubei, Nan'an and Yuzhong, the concentrations of second organic carbon were estimated as (2.0±1.8), (1.0±0.7) and (2.3±2.0) μg·m^-3 by OC/EC ratio method during days without rain and high concentration of O₃. The ratios of second organic carbon (SOC) in organic carbon (OC) were lower than 30%. The contribution of SOC to total OC was the highest in Yuzhong. This was possibly due to the formation of the urban heat island effect and the obviousness of the heat and radiation effect, which are beneficial to SOC generation through photochemical reaction. By calculating and analyzing the abundances of eight carbon components in PM_2.5, it is indicated that motor vehicle emissions are the major sources of carbon components at the three sites.