Ambient air aerosols, total polycyclic aromatic hydrocarbons (PAHs) for day and night time in the traffic areas of Central Taiwan

Abstract

Day and night time ambient air samples from a traffic intersection were collected using Noll Rotary Impactor (NRI) and micro‐orifice uniform deposited impactor (MOUDI) samplers from June 1997 to August 1997 in central Taiwan to characterize the atmospheric particle mass, total Polycyclic aromatic hydrocarbons (PAHs) size distribution and total PAHs content for the day and night period in a traffic area. Twenty‐one individual PAHs were qualified and quantified by gas chromatography/mass spectrometry (GC/MS). The particle size distribution shifted to the coarse particle mode as the wind speed increased and shifted to the fine particle mode as the wind speed decreased in day and night time. Both coarse and fine particle concentrations in the day time were larger than that for night time. In addition, the ratios of the coarse to the fine particle concentrations ranged from 0.53 to 0.94 in the night time. This displayed the influence of traffic flow rate on the particle concentration differences in the day and night period. The correlation coefficients (R2) of particle concentration vs. wind speed were 0.64 and 0.34 for coarse and fine particles, respectively in the day time. It indicated that the higher the wind speed the higher the coarse particle concentration. The total PAHs size distribution for both day and night time were bimodal and the major bi‐peaks were located in the particle size range 0.31 ‐0.52 μm and 1.8–3.2 μm, respectively. In general, fine particles (<2.5 μm) have higher PAH content. This is due to the fact that soot from combustion sources consists primarily of fine particles and has a high PAH content. For particle size from 0.31 to 3.2 μm the mean total PAHs content were 5262 and 1738 μg/g for day and night time, respectively.