One-year measurement of organic and elemental carbon in size-segregated atmospheric aerosol at a coastal and suburban site in Southeast China

Abstract

To understand the influence of the urbanization process on the air quality in the urban neighbourhood area, the size distribution and seasonal variations of elemental and organic carbon in aerosols were studied at a coastal and suburban site in Xiamen City, China. A total of 87 samples were obtained during the one-year measurement campaign from June 2009 to May 2010. The results indicated that 79.3 ± 3.2% of the organic carbon (OC) and 88.3 ± 1.7% of the elemental carbon (EC) were associated with fine particles (PM_2.5), which consist of 32.0 ± 8.3% of the total carbonaceous aerosol (TCA). The concentrations of the OC and EC in PM_2.5 were 17.8 ± 11.2 and 3.8 ± 1.9 μg m⁻³, respectively, and high concentrations were usually observed when the wind direction was northeast (NE). High OC/EC ratios (average 5.1) in PM_2.5 indicated the formation of secondary organic carbon (SOC), which contributed 60.0% to the OC and 11.0% to the particulate matter. At this site, SOC had a significant negative correlation with the temperature (R² = 0.42), and a favorable meteorological condition for SOC formation was found in the wintertime. The OC/EC ratios increased with particle size, while the fractions of the carbonaceous aerosols to particulate matter decreased. OC, EC and SOC concentrations and OC/EC ratios followed the same seasonal pattern of winter > spring > autumn > summer, which mainly resulted from the various origins of the air masses in different seasons. This study indicates the requirement for mitigating the pollution of carbonaceous aerosol at this coastal and suburban area in Xiamen City.