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.

PM_2.5  /  organic carbon  /  elemental carbon  /  thermal optical reflection  /  summer