Fine particulate matters: The impact of air quality standards on cardiovascular mortality

In 1997 the U.S. Environmental Protection Agency set the first annual National Ambient Air Quality Standard (NAAQS) for fine particulate matter (PM_2.5). Although the weight of scientific evidence has determined that a causal relationship exists between PM_2.5 exposures and cardiovascular effects, few studies have concluded whether NAAQS-related reductions in PM_2.5 led to improvements in public health.

We examined the change in cardiovascular (CV) mortality rate and the association between change in PM_2.5 and change in CV-mortality rate before (2000-2004) and after implementation of the 1997 annual PM_2.5 NAAQS (2005-2010) among U.S. counties. We further examined how the association varied with respect to two factors related to NAAQS compliance: attainment status and design values (DV). We used difference-in-differences and linear regression models, adjusted for sociodemographic confounders.

Across 619 counties, there were 1.10 (95% CI: 0.37, 1.82) fewer CV-deaths per year per 100,000 people for each 1µg/m³ decrease in PM_2.5. Nonattainment counties had a twofold larger reduction in mean annual PM_2.5, 2.1µg/m³, compared to attainment counties, 0.97µg/m³. CV-mortality rate decreased by 0.59 (95% CI: -0.54, 1.71) in nonattainment and 1.96 (95% CI: 0.77, 3.15) deaths per 100,000 people for each 1µg/m³ decrease in PM_2.5 in attainment counties. When stratifying counties by DV, results were similar: counties with DV greater than 15µg/m³ experienced the greatest decrease in mean annual PM_2.5 (2.29µg/m³) but the smallest decrease in CV-mortality rate per unit decrease in PM_2.5, 0.73 (95% CI: -0.57, 2.02).

We report a significant association between the change in PM_2.5 and the change in CV-mortality rate before and after the implementation of NAAQS and note that the health benefits per 1µg/m³ decrease in PM_2.5 persist at levels below the current national standard.

US EPA intermural research.