Modification of the Versatile Aerosol Concentration Enrichment System (VACES) for conducting inhalation exposures to semi-volatile vapor phase pollutants

A novel sampling system was developed to provide concentrated vapor phase only semi-volatile organic species for in-vivo exposure studies. The system consists of two units: particles (including their semi-volatile component) are first concentrated by means of the Versatile Aerosol Concentration Enrichment System (VACES), and subsequently drawn through a heating section, in which semi-volatile particle-bound components partition to the gas phase, while non-volatile particles are removed by a quartz filter placed after the heater. The vapors are then cooled to ambient temperatures, without producing nano-particles by nucleation, and can be readily used for exposure studies. Laboratory tests were carried out at various heater temperatures using ammonium sulfate, adipic acid and glutaric acid to investigate the occurrence of nucleation in the cooling section. Subsequently the system was tested in the field with concentrated particle and vapor samples taken upstream of the heater, immediately downstream of the filter, and after the cooling section. Chemical analysis of particle and vapor phases upstream and downstream of the system was conducted for selected polycyclic aromatic hydrocarbons (PAHs), and showed very good PAH recovery. These tests indicate that the modified VACES-heater-filter (VHF) system can provide concentrated PM (including their semi-volatile compounds) and PM-bound semi-volatile species purely in the vapor phase for inhalation exposure studies separately, a feature that makes this system an attractive approach for toxicity studies, particularly in light of the increasing interest in health effects of exposures to multi-pollutant atmospheres.