Sulfuric acid-layered ultrafine particles potentiate ozone-induced airway injury

Urban air pollution in the United States is composed of a complex mixture of particles and gases. Among the most prominent products of the atmospheric pollutants are sulfur oxides and ozone. In this report, we use two exposure protocols to examine the interaction between exposure to these two pollutants. In the first exposure regimen, guinea pigs were exposed to sulfuric acid (pure sulfuric acid mist or sulfuric acid layered on ZnO) for 1 h. Each exposure is followed 2 h later by another exposure to 0.15 ppm ozone for 1 h. Pulmonary function parameters were measured immediately after the ozone exposure. In guinea pigs that were exposed to 300 micrograms/m3 pure sulfuric acid mist, subsequent exposure to 0.15 ppm ozone did not produce additional change in pulmonary functions. In guinea pigs that were exposed to 84 micrograms/m3 sulfuric acid layered on ZnO, subsequent exposure to 0.15 ppm ozone produced more than additive alterations in vital capacity and diffusing capacity. In the second exposure regimen, guinea pigs were exposed to 24 micrograms/m3 sulfuric acid layered on ZnO for 3 h/d for 5 d. On d 8 and 9, animals received two additional daily 3-h exposures to 24 micrograms/m3 sulfuric acid layered on ZnO, and pulmonary functions were measured at the end of the daily exposure. Greater reductions in lung volumes and diffusing capacity were observed in animals on d 9 than would be observed in animals that received no additional exposure. In the third exposure regimen, guinea pigs were exposed to 24 micrograms/m3 sulfuric acid layered on ZnO for 3 h/d for 5 d. On d 9, animals were exposed to 0.15 ppm ozone for 1 h and pulmonary functions were measured at the end of the ozone exposure. Ozone exposure on d 9 induced reductions in lung volumes and diffusing capacity that were not observed in animals receiving exposures to either ozone or sulfuric acid layered ZnO alone. We conclude that single or multiple exposure to sulfuric acid-layered ZnO sensitizes guinea pigs to subsequent sulfuric acid or ozone exposure.