Abstract
During July 2002, forest fires in Quebec, Canada, blanketed the US East Coast with a plume of wood smoke. This "natural experiment" exposed large populations in northeastern US cities to significantly elevated concentrations of fine particulate matter (PM(2.5)), providing a unique opportunity to test the association between daily mortality and ambient PM(2.5) levels that are uncorrelated with societal activity rhythms. We obtained PM(2.5) measurement data and mortality data for a 4-week period in July 2002 for the Greater Boston metropolitan area (which has a population of over 1.7 million people) and New York City (which has a population of over 8 million people). Daily average PM(2.5) concentrations were markedly increased for 3 days over this period, reaching as high as 63 μg/m(3) for Greater Boston and 86 μg/m(3) for New York City from background ambient levels of 4-48 μg/m(3) in the non-smoke days. We examined temporal patterns of natural-cause deaths and 24-h ambient PM(2.5) concentrations in July 2002 and did not observe any discernible increase in daily mortality subsequent to the dramatic elevation in ambient PM(2.5) levels. Comparison to mortality rates over the same time periods in 2001 and 2003 showed no evidence of impact. Results from Poisson regression analyses suggest that 24-h ambient PM(2.5) concentrations were not associated with daily mortality. In conclusion, substantial short-term elevation in PM(2.5) concentrations from forest fire smoke were not followed by increased daily mortality in Greater Boston or New York City.