Associations between respiratory health and ozone and fine particulate matter during a wildfire event

During the active fire periods, PM2.5 was significantly associated with exacerbations of asthma and chronic obstructive pulmonary disease (COPD) and these effects remained after controlling for O-3. Effect estimates of O-3 during the fire period were non-significant for respiratory hospitalizations but were significant for ED visits for asthma (RR = 1.05 and 95% CI = (1.022, 1.078) for a 10 ppb increase in O-3). In mutually-adjusted models, the significant findings for PM2.5 remained whereas the associations with O-3 were confounded.

Adjusted for O-3, the RR for asthma ED visits associated with a 10 mu g/m(3) increase in PM2.5 was 1.112 and 95% CI = (1.087, 1.138). The significant findings for PM2.5 but not for O-3 in mutually-adjusted models is likely due to the fact that PM2.5 levels during these fires exceeded the 24-hour National Ambient Air Quality Standard (NAAQS) of 35 mu g/m(3) for 4976 ZIP-code days and reached levels up to 6.073 times the NAAQS, whereas our estimated O-3 levels during the fire period only occasionally exceeded the NAAQS of 70 ppb with low exceedance levels.

Future studies should continue to investigate the combined role of O-3 and PM2.5 during wildfires to get a more comprehensive assessment of the cumulative burden on health from wildfire smoke.