Size distributions of elemental carbon and its contribution to light extinction in urban and rural locations in the pearl river delta region, China

Elemental carbon (EC) in size-segregated aerosol samples were determined at five urban, one suburban, and one rural locations in the Pearl River Delta region in South China during 2006-2008 period. The size modal characteristics of EC were different at the urban and suburban/rural locations. The urban EC had a dominant condensation mode with a mass median aerodynamic diameter (MMAD) in the 0.36-0.43 μm range and a slightly less abundant mode in the droplet mode size (MMAD: 0.8-1.1 μm), while the suburban/rural EC had a prominent mode in the droplet mode size (MMAD: 0.7-1.1 μm) and a minor condensation mode (MMAD: 0.22-0.33 μm). Calculations using Mie theory and the measured size distributions of EC, organic carbon, and major inorganic ions indicate that EC-containing particles contributed 76±20% of the observed light extinction at the urban sites. Among the EC-containing particles, EC mass alone contributed 21±11% of the observed light extinction while non-EC materials on the EC particles (i.e., organic matter, ammonium sulfate, and water) contributed 55±15%. At the suburban/rural locations, EC-containing particles contributed 37g-48% of the measured light extinction, with EC mass contributing 4-10% and non-EC coating materials contributing the remaining light extinction. Our results suggest that EC-containing particles were important to the overall light extinction in the urban atmospheres due to their more abundant presence from vehicular emissions. The EC-containing particles in the suburban/rural locations had a reduced but still significant contribution to light extinction budget.