Measurements of Atmospheric Radicals

Atmospheric particulate matter (PM) is a global health concern. PM2.5 is formed primarily through combustion processes such as automobile use and industrial activity. Natural sources of PM2.5 result from events like volcanos and wildfires. Upon inhalation, PM2.5 is small enough to travel deep into the lungs where it can form reactive oxygen species (ROS), such as hydroxyl radical (OH), causing oxidative damage to pulmonary tissues. PM2.5 has been linked to cardiopulmonary diseases such as asthma, chronic obstructive pulmonary disease (COPD), and high blood pressure. PM2.5 is small enough to remain aloft and travel many hundreds of miles from its source of origin. During this time, the PM2.5 undergoes atmospheric aging as it is exposed to reactive gasses in the air, as well as photoreactions upon exposure to sunlight, potentially making the PM components more toxic. Two significant fractions of PM2.5 are polycyclic aromatic hydrocarbons (PAH) and environmentally persistent free radicals (EPFR). Many PAH are photoactive and oxidize in the atmosphere into derivatives that can cause more oxidative damage than the parent compounds (oxPAH). Both PAH and EPFR are formed during the combustion process, and both have been suggested as the source the oxidative toxicity of PM2.5. The studies reported here explore the aging of PAH, oxPAH, and EPFR as well as their ability to generate reactive oxygen species in simulated cloud waters. The first study investigates the stability of EPFR on hexane-derived soot, used as a surrogate for PM2.5, in ambient conditions. Additionally, a new lower limit on EPFR from environmental PM2.5 samples was determined resulting in a significant improvement in time-resolution measurements of ambient EPFR. In the second study, concentrations of OH were measured of select PAH and oxidized-PAH in conditions designed to mimic individual cloud droplets exposed to sunlight. Significant concentrations of OH were observed, as well as the formation of many new products. And finally, the last study investigates the intersection of the two, quantifying OH formation from both fresh and photo-aged hexane-derived soot and measuring changes to the soot’s EPFR character. Photo-aged soot was found to produce almost 60% less OH than fresh soot