Measuring the Impacts of Air Pollution Reduction Strategies on Respiratory Hospitalizations in Minnesota

NAOMI SHINODA (1), Jean Johnson (1), Paula Lindgren (1), Allan Williams (1), Gregory Pratt (2), Kari Palmer (2), Margaret McCourtney (2), Lisa Herschberger (2), Barbara Yawn (3), Chuck Stroebel (1)

(1) Minnesota Department of Health, (2) Minnesota Pollution Control Agency, (3) Olmsted Medical Center, Rochester, MN

     Abstract Number: 285
     Last modified: November 9, 2009

Abstract
Several studies have shown associations between ambient particulate matter (PM) and respiratory health effects, leading to more stringent National Ambient Air Quality Standards (NAAQS) for fine particles (PM2.5). Although the Minneapolis-St. Paul (MSP) metropolitan area is a designated NAAQS “attainment” area, studies have suggested that air pollution-related adverse health effects have continued to occur. However, the impacts of the most recent air pollution reduction strategies on population exposure and related health outcomes in this metropolitan area have not been addressed.

Several ongoing local and regional air pollution reduction strategies are being implemented in the MSP metropolitan area. The Minnesota Emissions Reduction Project is a voluntary $1 billion energy project that involved the conversion of two coal-fired power plants to natural gas and the installation of new emissions control equipment on a third plant in 2008 and 2009. The Project Green Fleet and Congestion Mitigation Air Quality programs, which have retrofitted approximately 900 school buses and 330 heavy duty public vehicles during 2006-2009, are expected to reduce PM exposures from traffic-related sources. On a national level, the ultra low sulfur diesel fuel rule was phased in nationwide in late 2006, in addition to a 2007 rule requiring new stringent emission standards for heavy duty diesel engines.

In this work, we present the development of environmental health outcome indicators and analytical methods to track the impacts of air pollution reduction strategies on acute respiratory hospitalizations over an eight-year study period (2002-2009) in the MSP metropolitan area. We use a case-crossover analytical design with a time-stratified referent selection approach to assess associations between exposure lags of daily 24-hour continuous PM2.5 monitoring data and total respiratory, chronic lower respiratory disease, and asthma hospitalizations. Using conditional logistic regression models that adjust for temperature, relative humidity, influenza epidemics, and national holidays, we generate risk estimates and population attributable fractions (AFp) for the first six years of the study period, comparing estimates from the baseline (2002-2004) and early-implementation (2005-2007) years.

Our findings show significant positive associations between PM2.5 and all three respiratory health outcomes during 2002-2007. Preliminary results suggest that risk estimates for the PM exposure-hospitalization associations decreased slightly during 2005-2007 compared with the baseline period. There were significant associations between the three-day mean (lag0-2) of PM2.5 and all three respiratory health outcomes during 2002-2004; during 2005-2007, these associations were no longer statistically significant. Preliminary AFp estimates also show a change between the two time periods.

Despite some remaining uncertainties in the analyses, the preliminary results for years 2002-2007 are encouraging. As the majority of local air pollution reduction strategies took place during 2008 and 2009, we anticipate that employing the analytical methods described here during those implementation years will help to further assess not only the impacts of the pollution reduction strategies, but also the utility of these methods for tracking those public health impacts.