Background: The potential of diesel soot aerosol particles to break up into smaller units under mechanical stress was investigated by a direct impaction technique which measures the degree of fragmentation of individual agglomerates vs. impact energy. Diesel aerosol was generated by an idling diesel engine used for passenger vehicles. Both the aerosol emitted directly and aerosol that had undergone additional growth by Brownian coagulation ("aging") was investigated. Optionally a thermo-desoption technique at 280°C was used to remove all high-volatility and the majority of low-volatility HC adsorbates from the aerosol before aging.

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Aerosols of submicron polystyrene particles were oxidized by either vacuum-ultraviolet (VUV) irradiation in the presence of molecular oxygen (O(2)) and/or by ozone (O(3)). Different degrees of oxidation and oxidative degradation were reached by VUV-photolysis depending on radiant energy, O(2) and H(2)O concentrations in the bulk gas mixture as well as on particle diameter. The same functionalization was obtained by exposing the aerosol to O(3), however, oxidation, in particular oxidative degradation, was less efficient. The evolution of hydroxyl and carbonyl functions introduced was quantified by ATR-FTIR spectroscopy of filtered particles, and oxidative degradation of the polymer particles was confirmed by determining size and number of aerosol particles before and after oxidation. Efficiency analyses are based on the results of an O(3) actinometry and on an evaluation of the rate of absorbed photons by the aerosol particles in function of their size.

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The up-scaling of an earlier described VUV-photochemical oxidative functionalization of polystyrene aerosols depends primarily on the possibility to increase substantially the particle concentration in the gas phase, the aerosol flux and the rate of oxidation. The VUV-photolysis of tetrachloro-methane (CCl 4 ) in the presence of air was chosen for the initiation of the oxidation of the polystyrene surface (photo-oxychlorination) taking advantage of the excellent solvent characteristics and the high absorption cross section. FTIR spectroscopic analyses confirm the high efficiency of the process, and chlorination, crosslinking and oxidative particle fragmentation remained at low yields. Secondary products of the VUV-photolysis of CCl 4 were trapped and did not interact with the functionalized particles.