Abstract
Hourly organic carbon (OC) and elemental carbon (EC) concentrations in PM2.5 were measured from June 2013 to May 2014 in Wanzhou, the second largest city in the Chongqing Municipality, in the southwest of China. Results show that the annual average concentrations of OC and EC were 13.16 ± 7.98 and 3.12 ± 1.51 μgC·m−3, respectively. Clear seasonal variations of OC and EC concentrations were observed, with their concentrations at minima in summer and maxima in winter. The diel concentration profile of OC and EC presented a bimodal pattern, which was attributed to the cooperative effects of local meteorological conditions and source emissions. The daily average OC/EC ratio ranged from 2.05 to 8.17 with an average of 4.15 for the whole study period. Strong correlations between OC and EC were found in winter and spring, indicating their common sources, while their correlations were poorer in summer and autumn, indicating that the influence of biogenic emissions and secondary organic carbon (SOC) were significant during those seasons. The estimated SOC concentrations were 2.19 ± 1.55, 7.66 ± 5.89, 5.79 ± 3.51, and 3.43 ± 2.26 μgC·m−3, accounting for 29.2%, 52.7%, 27.4%, and 30.5% of total organic carbon in summer, autumn, winter, and spring, respectively. The analysis of back trajectories suggested that high PM2.5, OC, and EC concentrations were associated with air masses originating from or passing over several industrial centers and urban areas in western and northwestern China. Air trajectories from the southeast with short pathways were the dominant trajectories arriving at Wanzhou, indicating that local sources had a big influence on PM2.5, OC, and EC concentrations.
Highlights
Carbonaceous aerosol—which contributes 20–60% to PM2.5 mass in urban settings [1,2,3,4]—has been found to have a large impact on environmental conditions, such as visibility and climate change [5,6,7,8]
Carbonaceous aerosol is usually separated into elemental carbon (EC) and organic carbon (OC)
The ambient air was first sampled into a PM2.5 cyclone inlet with a flow rate of 8 L·min−1, and passed through a carbon parallel-plate diffusion cyclone inlet with a flow rate of 8 L·min−1, and passed through a carbon parallel-plate diffusion denuder to remove volatile organic compounds that may cause a positive bias in denuder to remove volatile organic compounds that may cause a positive bias in the OC concentrations measured [39]
Summary
Carbonaceous aerosol—which contributes 20–60% to PM2.5 mass in urban settings [1,2,3,4]—has been found to have a large impact on environmental conditions, such as visibility and climate change [5,6,7,8]. As the basic components of carbonaceous aerosol, temporal and spatial variations of OC and EC concentrations in PM2.5 have been presented in several studies [14,15,16,17]. China has drawn significant attention worldwide due to its rapid industrialization and increased consumption of fossil fuels and biofuels, which result in increased primary sources of carbonaceous aerosol [27,28]. Along with other small cities in China in recent years, Wanzhou has experienced especially rapid urbanization and industrialization, with the annual growth rates of GDP and amount of automobiles (0.21 million vehicles by the end of 2014) increasing by more than 10% in the last five years (http://www.cqtj.gov.cn/tjnj/2014/indexch.htm). (3) to identify the sources and factors affecting carbonaceous aerosols in Wanzhou
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