Gas/particle Partitioning and Particle Size Distributions of Polycyclic Aromatic Hydrocarbons (pahs) in the Atmosphere.

This study applied three different gas/particle (G/P) separation mechanisms (diffusion, filtration and impaction) to investigate G/P partitioning and particle size distributions of polycyclic aromatic hydrocarbons (PAHs) in the atmosphere. Because some PAHs such as benzo (a) pyrene have been shown to be carcinogenic to humans and persistent in the environment, it is important to have reliable methods to measure PAH G/P partitioning and particle size distributions for the purpose of understanding their atmospheric processing and their impact to environmental and human health. The objectives of this study include: (1) Development of a diffusion separator (DS) to separate a known fraction of the gas phase from the aerosol: The calibration experiment results reveal that the G/P separation performance of the DS agrees well with diffusion theory. True gas PAH concentrations are calculated by the measured PAH concentrations in the core exit of the DS and the diffusion factor at the sampling temperature. (2) Evaluation of sampling artifacts associated with high volume samplers and their effectiveness in measuring PAH G/P partitioning in the atmosphere: The comparison between the DS, a filter/adsorbent sampler (FA) and a microorifice uniform deposit impactor (MOUDI) revealed both gaseous sorption onto filters and desorption from filters of the FA sampler for most PAHs. (3) Investigation of particle size distribution of PAHs in Chicago urban and Minnesota suburban areas: The results of MOUDI sampler showed that the PAH mass median diameters (MMDs) are smaller than atmospheric particle MMDs by 0.1-0.3 μm in both areas. The calculated PAH dry deposition fluxes and Lake Michigan sediment accumulation rates indicates that the atmospheric dry deposition contributes 15-50% of PAHs to nearby Lake Michigan sediment.