Direct Measurement of the Impact of Atmospheric Processing on the Size and Properties of Sub- and Super-micron Aerosol Particles

Secondary aerosol is created when gases in the atmosphere are oxidized, usually through reactions with ozone or hydroxyl radical, creating low vapor pressure products that condense on existing particles or form new ones. This study was partly motivated by differences between the rate at which observed particle size and properties change due to condensation of secondary aerosol products in ambient air and under controlled laboratory conditions. It also functioned as the first field deployment of a pair of portable chambers designed to study particle growth rates in different areas. Field work took place at WG Jones State Forest located downwind of the Houston metropolitan area. This site is impacted by both anthropogenic and biogenic emissions, with the prominence of the two emission types strongly dependent upon wind direction. Due to high emission of monoterpenes from the surrounding forest, the majority of secondary aerosol formed was likely organic. With the use of the mobile Captive Aerosol Growth and Evolution (mCAGE) environmental chambers, the impact of atmospheric reactions on captive aerosol populations were examined by mimicking environmental conditions. Through cooperation with Sandia National Laboratories, this experiment was designed to study the creation of secondary aerosol, and to measure its impact on the viability and fluorescence characteristics of primary biological particles such as bacterial spores. Preliminary results indicate that the bioaerosols were rapidly altered. Attributing the observed changes to UV radiation and secondary aerosol condensation is the focus of continuing work.