The partitioning of polycyclic aromatic hydrocarbons (PAHs) between the particulate and gaseous phases resulting from the combustion of polystyrene was studied. A vertical tubular flow furnace was used to incinerate polystyrene spheres (100-300 µm) at different combustion temperatures (800-1200 °C) to determine the effect of temperature and polystyrene feed size on the particulate and gaseous emissions and their chemical composition. The furnace reactor exhaust was sampled using real-time instruments (differential mobility particle sizer and/or optical particle counter) to determine the particle size distribution. For chemical composition analyses, the particles were either collected on Teflon filters or split into eight size fractions using a cascade impactor with filter media substrates, while the gaseous products were collected on XAD-2 adsorbent. Gas chromatography/mass spectroscopy (GC/MS) was used to identify and quantify the specific PAH species, their partitioning between the gas and particulate phases, and their distribution as a function of emission particle size. The total mass and number of PAH species in both the particulate and gas phases were found to decrease with increasing incineration temperature and decreasing polystyrene feed size, while the mean diameter of the particles increases with increasing incineration temperature and decreasing feed size. In addition, the PAH species in the particulate phase were found to be concentrated in the smaller aerosol sizes. The experimental results have been analyzed to elucidate the formation mechanisms of PAHs and particles during polystyrene combustion. The implications of these results are also discussed with respect to the control of PAH emissions from municipal wasteto-energy incineration systems.

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Abstract. During the Indian Ocean Experiment (INDOEX), cloud droplets were collected and evaporated using a counterflow virtual impactor (CVI). The nonvolatile residual particles were then analyzed by various instruments. Physical and chemical properties of the cloud droplets and their residual nuclei were compared with properties of the below-cloud aerosol to evaluate which aerosol particles act as cloud nuclei in different environments, and their effects on cloud microphysics. Four cases, ranging from clean Southern Hemispheric clouds to heavily polluted clouds near India, were analyzed. For the cleaner clouds, droplet concentrations were a much higher fraction of the available particle concentrations than for polluted clouds, but entrainment apparently acted to reduce droplet number concentrations in both regimes. For clean clouds the median critical supersaturation and size of the ambient particles and droplet residual particles were similar. In polluted clouds there were stronger differences between ambient and droplet residual distributions, and particles with lower critical supersaturations were favored as nuclei. Simple model calculations were used to show that polluted clouds are expected to achieve lower water supersaturations than clean clouds; thus only particles with relatively low critical supersaturations are likely to affect clouds in polluted regions. Soluble fractions for the ambient aerosol inferred from the size and cloud condensation nuclei measurements were in general agreement with another study in the region. Droplet residual particles did not necessarily have higher soluble fractions than the ambient aerosol, but did tend to have higher total amounts of soluble material per particle, particularly in the polluted cases.