CHARACTERIZATION OF ATMOSPHERIC DRY DEPOSITED PARTICLES AT URBAN AND NON-URBAN LOCATIONS

Abstract

Microscopic techniques were used to size particles collected on a deposition surface and to generate mass size distributions of deposited particles sampled from urban and non-urban locations. The volume shape factor was defined as a conversion factor between the projected area diameter and equivalent volume diameter of a particle and was used as an indication of the irregularity of the particle shape. The average volume shape factor of deposited particles at the urban location (1.61±0.21) was higher than the average at the non-urban locations (1.16±0.10). This suggests that particles are more irregular in the urban areas. Since non-urban areas have less larger particles in ambient air, depositional mass-size distributions at the urban location had a larger average peak (58 μm) and average mass median diameter (49 μm) of coarse particle mode of the distributions than they did at non-urban locations (averaged 33 and 27 μm). Evaluation of correlation coefficients between parameters (wind speed, deposition flux, peak diamater, mass median diameter) indicates that there are more airborne coarse particles at urban locations than at non-urban locations and this distribution plays an important role in dry deposition. By directly observing the deposited particles, it was found that particles larger than 10 μm diameter contributed to more than 90% (in mass) of the atmospheric dry deposition even when ambient coarse particle concentration is low at non-urban locations.