Synergistic Effects of Ozone Reaction Products and Fine Particulate Matter on Respiratory Pathophysiology in Children with Asthma

After being transported from outdoor to indoor environments, a large portion of ozone (O3) reacts with indoor chemicals to generate O3 reaction products. A fraction of these products can partition to fine particulate matter (PM2.5). Hence, we hypothesize that PM2.5 serves as a carrier to deliver O3 reaction products to the deep lung, leading to synergistic adverse pulmonary effects. In a panel study involving 43 children with asthma, each was assessed 4 times (2-week interval) for biomarkers of respiratory pathophysiology and personal exposures to PM2.5 and O3. We also assessed O3 loss exposures, calculated by taking the difference between the outdoor and indoor O3 concentrations, which was proportional to the net exposure to O3 reaction products. We found the adverse effects of O3 loss exposure on biomarkers of pulmonary inflammation, airway (especially lower airway) mechanics, and spirometry lung function were greater at higher PM2.5 exposure levels. We also found that the adverse effects of PM2.5 exposure were greater at higher O3 loss exposure levels. This suggests an additional mechanism for the synergistic pulmonary effects: PM2.5 predisposes the lung to be more susceptible to O3 reaction products and vice versa. However, our data is limited in differentiating the two potential mechanisms.