Characterization of atmospheric dry deposited particles at urban and non-urban locations

Microscopic techniques were used to size particles collected on a depositio n surface and to generate mass size distributions of deposited particles sa mpled from urban and non-urban locations. The volume shape factor was defin ed as a conversion factor between the projected area diameter and equivalen t volume diameter of a particle and was used as an indication of the irregu larity 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 a re more irregular in the urban areas. Since non-urban areas have less large r particles in ambient air, depositional mass-size distributions at the urb an location had a larger average peak (58 mu m) and average mass median dia meter (49 mu m) of coarse particle mode of the distributions than they did at non-urban locations (averaged 33 and 27 mu m). Evaluation of correlation coefficients between parameters (wind speed, deposition flux, peak diamate r, mass median diameter) indicates that there are more airborne coarse part icles at urban locations than at non-urban locations and this distribution plays an important role in dry deposition. By directly observing the deposi ted particles, it was found that particles larger than 10 mu m diameter con tributed to more than 90% (in mass) of the atmospheric dry deposition even when ambient coarse particle concentration is low at non-urban locations. ( C) 1999 Elsevier Science Ltd. All rights reserved.