In the 112 cities during the study period 1999–2005, there were 5,609,349 total deaths, 1,787,078 for CVD, 397,894 for MI, 330,613 for stroke, and 547,660 for respiratory disease. The biggest cities are Los Angeles, California; New York City, New York; and Chicago, Illinois.
The cities with higher levels of PM2.5 were in California, with maximum concentrations of PM2.5 > 100 μg/m3, whereas the cities with the lower maximum levels were in Oklahoma. The median PM2.5 ranged from 5.6 μg/m3 in Albuquerque, New Mexico, followed by Eugene and Bend, Oregon, with 6 μg/m3, whereas the highest median concentrations were 21.5 μg/m3 in Rubidoux, California, and 17.4 μg/m3 in Los Angeles.
in Supplemental Material (available online at http://www.ehponline.org/members/2009/0800108/suppl.pdf
) presents the following for each of the 112 cities: the years of study, the daily mean concentration levels for PM2.5
and PM coarse, and the daily mean number of death by cause.
shows the location of the 112 U.S. cities included in the study; the symbol size represents the population in each city, and the color represents the PM2.5 concentrations. High levels of PM2.5 (red) are in California and in the industrial Midwest.
shows the percent increase in mortality for a 10-μg/m3 increase in PM2.5 for the mean of lags 0 and 1 (henceforth mean01), for the mean01 by season.
We found significant associations with all the analyzed causes of death and PM2.5, with the highest effect for stroke with a 1.78% increase [95% confidence interval (CI), 0.96–2.62], and respiratory mortality with a 1.68% increase (95% CI, 1.04–2.33) for a 10-μg/m3 increase in the mean01 of PM2.5. When looking at the results by season, the highest effects are in spring, with > 2% increases.
shows the percent increase in mortality for a 10-μg/m3 increase in PM coarse across the 47 cities for the sum of the 4 days distributed lag model and by season. We found significant associations with total mortality, stroke, CVD, and respiratory mortality, for which we had the largest effect: a 1.2% increase (95% CI, 0.4–1.9) for a 10-μg/m3 increase in PM coarse. The effect sizes per unit of mass for PM coarse are about half those for PM2.5.
Combined results across 47 cities of the mortality PM coarse association for the mean01 and for the mean01 by season.
When we examined the distributed lag for PM coarse (), we found little evidence that the effects were at longer lags. reports the percent increase in cause-specific mortality at each lag from the distributed lag model, combined across the 47 cities. There were indications of some effect at lag 2, but the sum of the distributed lag was not higher than the results for mean01.
Percent increase in cause-specific mortality for the 4 days distributed lag model, combined in 47 cities for PM coarse. Error bars represent 95% CIs of the estimates.
When looking at the heterogeneity by season, we found no significant heterogeneity in general in summer (), whereas significant heterogeneity was seen in spring and autumn. For all-cause mortality and PM2.5, 32% in spring and 15% in autumn of the total variability in city-specific coefficients was attributable to between-community differences (as opposed to stochastic variation). For PM coarse, we only found significant city-specific heterogeneity for all-cause and respiratory mortality. Again, the highest percentage of explained total variability was in spring.
shows the results from the multipollutant model, which included both PM2.5 and PM coarse. There were only minor changes in the effect size estimates for either pollutant, and both remained significant for all-cause mortality, although some of the cause-specific results had increased CIs that included no effect.
Percent increase (95% CI) in mortality for 10-μg/m3 increase in PM coarse and PM2.5 for the mean01 across the 47 cities; two-pollutant model and single-pollutant model results for PM2.5 in 47 cities.
shows the effects for PM2.5 and PM coarse by region. The number of cities varied in each region and by pollutant. For PM2.5 in the six regions, we have 47, 28, 17, 2, 3, and 15 cities, respectively. For PM coarse, we have 15, 11, 11, 2, 3, and 5 cities. The regions with dry climates and together with continental climate are the regions with the lower number of cities because they are not very populated, but they have the same number of cities for both PM2.5 and PM coarse. The effects of PM2.5 on all-cause mortality are similar for all regions except for the last (Mediterranean), which include California, Oregon, and Washington. The results were more varied for the specific causes of death, but the precision of the estimates was also less. There was a consistent trend for lower effects in the Mediterranean region for each cause as well.
Percent increase (95% CI) in mortality for 10-μg/m3 increase in the mean01 PM2.5 and PM coarse, combined by regions.
In contrast, the pattern was different for coarse particles. First, there was considerably more variation in general in the all-cause mortality effects by region. Not only was the Mediterranean region different (as for PM2.5); there was no effect in the dry region as well. In addition, the effect size in the dry continental region was double that in the humid subtropical region for all-cause mortality and triple for CVD deaths.
The percentage of explained total variability differed between regions and between the two pollutants, with significant heterogeneity in the “warm summer, continental,” “hot summer, continental,” and “Mediterranean” regions when looking at all-cause mortality and PM2.5; for PM coarse significant heterogeneity was found in “warm summer, continental” and “dry” regions.