Abstract
Daily PM2.5 samples were collected in the four consecutive seasons in 2013 in Wanzhou, the second largest city in Chongqing Municipality of China and in the hinterland of the Three Gorges Reservior on Yangtze River and analyzed for the mass concentrations and carbonaceous species of PM2.5 to investigate the abundance and seasonal characteristics of PM2.5, and organic carbon (OC) and elemental carbon (EC). The annual average PM2.5 concentrations were 125.3 μg·m−3, while OC and EC were 23.6 μg·m−3 and 8.7 μg·m−3, respectively. The total carbonaceous aerosol (TCA) accounted for 32.6% of the PM2.5 mass. On seasonal average, the OC and EC concentrations ranked in the order of winter > fall > spring > summer, which could be attributed to the combined effects of changes in local emissions and seasonal meteorological conditions. Strong OC-EC correlations were found in the winter and fall, suggesting the contributions of similar sources. The lowest OC-EC correlation occurred in the summer, probably due to the increases in biogenic emission and formation of secondary organic aerosol (SOA) through photochemical activity. Average secondary organic carbon (SOC) concentration was 9.0 μg·m−3, accounting for 32.3% of the total OC. The average ratios of SOA/PM2.5 of 3.8%~15.7% indicated that SOA was a minor fraction in fine particles of Wanzhou.
Highlights
IntroductionFine particulate matter (with aerodynamic diameter less than 2.5 μm, PM2.5) has drawn extensive attention in China because most Chinese regions are affected by the large-scale haze days [1]
In recent years, fine particulate matter has drawn extensive attention in China because most Chinese regions are affected by the large-scale haze days [1]
The seasonal characteristics of PM2.5 concentrations in Wanzhou can be explained as the combined impact of climatic conditions and local emissions
Summary
Fine particulate matter (with aerodynamic diameter less than 2.5 μm, PM2.5) has drawn extensive attention in China because most Chinese regions are affected by the large-scale haze days [1]. In 2012, China’s state environmental protection department revised the original ambient air quality standards, the revised standard added limits to PM2.5 (annual average limit 35 μg·m−3, daily average limit 75 μg·m−3). Carbonaceous fractions, as air pollutants, climate agents and represent the complexity of aerosols, are major components in fine particles, contributing 10%~70% of PM2.5 mass in urban atmosphere [2,3]. Bond et al [4] estimated that China contributes roughly one-fifth of the global carbonaceous emissions. It is necessary to conduct research in carbonaceous aerosol, especially in China. Carbonaceous species are usually classified into elemental carbon (EC) and organic carbon (OC)
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