Particle size distribution of aerosol carbons in ambient air

Abstract

The concentrations and size distributions of organic carbon (OC), elemental carbon (EC), and polycyclic aromatic hydrocarbons (PAHs) were measured with a PS-1 sampler, NRI (Noll Rotary Impactor), and MOUDIs (Micro-orifice Uniform Deposit Impactor) in the ambient air of the traffic intersection and rural site in the Ping Tung area of Southern Taiwan, from September 1994 to December 1995. An elemental analyzer was used to analyze the carbon composition of the aerosol samples. Twenty-one individual PAHs were analyzed primarily by a gas chromatography/mass spectrometer (GC/MS). In the ambient air of the traffic intersection (1.5 m height), the concentrations of EC were between 31.3 and 42.8 μg m −3, averaging 39.8 μg m −3; the concentration ratios for OC/EC ranged between 1.1 and 1.6 and averaged 1.4. Both TC/EC and OC/EC decreased as the height increased. The particle size distribution of OC, EC, and total-PAHs are all bimodal. The particle size distribution in the fine particle mode for OC, EC, and PAHs ranged from 0.18 to 0.32 μm. However, the particle size distribution in the coarse mode for EC and total-PAHs ranged from 5.6 to 10 μm. The major peaks of OC, EC, and total-PAHs particles size distribution located at the fine particle indicate not only the gas-to-particle condensation in the fine particle mode after those are emitted to the atmosphere, but also reveal some important information related to health hazards in the ambient air of the traffic intersection. The cumulative fraction of OC, EC, and total-PAHs in the particle size less than 1 μm was 70.3%, 75.1%, and 64.1%, respectively, while the values in the particle size less than 2.5 μm were 81.9%, 84.9%, and 73.9%, respectively. More than 93% of TC, OC, EC, and PAHs existed in the particle size less than 10 μm.