Particulate reactive oxygen species in indoor and outdoor environments : prevalence and health effects
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Reactive Oxygen Species (ROS) are an important class of air pollutants generated from photochemical and ozone-initiated reactions in indoor and outdoor environments. Despite the fact that Americans spend nearly 90% of their time inside buildings and extended exposures to ROS can occur in indoor environments, ROS has received very little attention as an indoor pollutant. This is one of the first research studies to measure the concentration of particulate ROS (on PM [subscript 2.5] and TSP) in indoor environments. A significant fraction of indoor particulate ROS was found to exist on PM [subscript 2.5] (58±10%) which is important from a health perspective since PM [subscript 2.5] can carry ROS deep into the lungs. The indoor concentrations of ROS on PM [subscript 2.5] sampled in residential and commercial buildings were not significantly different from the outdoor concentrations. This result is intriguing because it implies that generation of ROS inside buildings and/or transport of outdoor ROS and precursors of ROS into buildings are important processes and can be as significant as ROS generation in outdoor environments. Controlled studies show that when outdoor ozone concentrations are relatively low, indoor concentrations of ROS are dominated by indoor sources of ROS rather than outdoor sources of ROS. However, when outdoor ozone concentrations are relatively high, indoor and outdoor sources of ROS contribute almost equally to the indoor concentration of ROS. This study is also one of the first to assess seasonal variations in outdoor particulate ROS concentrations. Ambient sampling conducted over an 11-month period indicates that outdoor particulate ROS concentrations are influenced by the ozone concentration, solar radiation intensity and temperature. In order to understand the potential health effects of exposure to ROS, an in vitro exposure system of lung epithelial cells and differentiated lung tissue was also utilized. Results from these experiments indicate that exposure to products of limonene ozonolysis (which include ROS) can lead to a greater inflammatory response than exposure to either ozone or limonene. This highlights the need to include biologically relevant pollutants, such as ROS, in indoor air quality studies. Further work is warranted to better understand the parameters that drive indoor particulate ROS concentrations.