Atmospheric fate and transport of dioxins: local impacts

We conducted model simulations of the atmospheric fate and transport of PCD D/F to assess the fraction of emitted PCDD/F that would deposit within 100 km from the source. We considered eight major categories of PCDD/F emission sources and six different locations, to cover a wide range of source chara cteristics, PCDD/F congener profiles and particle size distributions, meteo rological conditions and terrain configurations. These results suggest that for sources that have tall stacks and/or high plume rise (e.g., copper sme lters, cement kilns, sinter plants), only a small fraction of PCDD/F emissi ons is deposited locally (typically, less than 10%, within 100 km). Other s ource categories such as municipal solid waste incinerators, medical waste incinerators and diesel trucks lead to a greater fraction of PCDD/F being d eposited locally; nevertheless, the majority of their PCDD/F emissions tend s to be transported beyond 100 km. Although local impacts may need to be ad dressed for these latter source categories, it appears that the long-range potential impacts of PCDD/F need to be addressed for all source categories. Sensitivity studies were conducted to investigate the effect of various ke y model inputs on simulation results. These studies suggest that an advance d atmospheric dispersion model should be used for cases where PCDD/F emissi ons may present some local concerns because the results are very sensitive to the treatment of dispersion. Also, it is essential to obtain accurate ch aracterizations of the particle size distribution of particulate PCDD/F bec ause the dry deposition flux is very sensitive to the particle size distrib ution. (C) 2001 Published by Elsevier Science Ltd.