The Utah Valley provided a unique opportunity to evaluate the health effects of particulate matter (PM) in humans. The area has had intermittently high particle levels with the principal point source being a steel mill. Due to a labor dispute, the mill was shut down. The closure and reopening of the steel mill allowed for an examination of potential correlates between epidemiological observations and measures of the biological effect of PM with experimental cell and human exposure. Epidemiologic investigation demonstrated an association of both the closure of the steel mill and the reduction in exposure to air pollution particles with changes in morbidity and mortality. Changes in these parameters were not fully accounted for by variation in the mass of PM. Metal content, in vitro oxidative stress, and release of pro-inflammatory mediators by cultured respiratory epithelial cells were all elevated in those aqueous extracts collected from the Utah Valley while the steel mill was open. Similarly, inflammatory injury in the lower respiratory tract of humans after instillation of aqueous extracts of filter PM was increased in those volunteers exposed to particles collected while the mill was open. These results indicate that equal masses of PM can induce disparate lung injuries suggesting that particle components may be relevant in assessing health effects after their exposure. Specifically, metals can participate in the biological effects of PM collected from the Utah Valley. In addition, correlates between findings of epidemiological studies and the biological effects of PM in cell and human investigation were demonstrated.