An exposure system to study the effects of water-soluble gases on PM-induced toxicity

An aerosol generation and exposure system to evaluate the role of water-soluble gases in particulate matter (PM)-induced injury was designed, built, and validated by generating test atmospheres to study the role of hydrogen peroxide in PM-induced toxicity. In this system, particle number concentration, size distribution, hydrogen peroxide concentration, and water concentration can all be varied. An ammonium sulfate aerosol with mass median diameter 0.46 +/- 0.01 microm was used as a model atmospheric aerosol because ammonium sulfate is a major component of the fine aerosol, and the water uptake of ammonium sulfate aerosol is well characterized. The following four test atmospheres were generated: (1) ammonium sulfate aerosol, (2) an aerosol containing hydrogen peroxide and ammonium sulfate, (3) vapor-phase hydrogen peroxide, and (4) particle-free air. All test atmospheres were maintained at a relative humidity of 85%. Particle size distribution, number concentration, total hydrogen peroxide concentration, temperature, and relative humidity were measured continuously in the exposure chamber. The gas-particle partitioning of hydrogen peroxide was calculated using total hydrogen peroxide concentration, the Henry's law constant for hydrogen peroxide in water, and aerosol water content. We found that the aerosol generation system produced stable concentrations throughout the 2-hour exposures.