Michelle L. Bell

Professor of Environmental Health


Air Pollution & Human Health

We research how exposure to air pollution affects human health, such as risk of premature mortality, hospital admissions, or adverse pregnancy outcomes. The research method often involves mathematical modeling with large datasets on air pollution, health, and weather, combined with knowledge of the underlying systems (e.g., the dynamics of pollutant formation). We estimate whether associations exist, but also the uncertainty of those estimates and how and why they vary across locations, time periods, and populations. An example is a study of ozone and mortality in 95 large U.S. communities covering about 40% of the U.S. population. In follow-up studies, we examined the degree to which particulate matter confounds observed ozone-mortality relationships and developed statistical approaches to estimate the exposure-response curve for ozone and mortality, finding risk at low concentrations nearing natural background levels and well below current regulations.  In addition to typical modern-day pollution, we study anomalous high pollution episodes, such as sandstorms in Taipei, Taiwan. We investigated the London Fog of 1952 (view image), a historically important episode that catalyzed scientific study and policy for air pollution. Our results indicate that thousands of deaths previously attributed to influenza are far more likely to be from air pollution. About 10,000-12,000 persons died from air pollution, rather than the 3,000-5,000 typically reported over the previous 50 years. Current projects include study of how air pollution affects risk of respiratory and cardiovascular hospitalizations for older populations, and how mother’s exposure to air pollution over pregnancy affects birth weight and preterm delivery. This research addresses which trimester of exposure is most important, including development of mathematical models to address co-variance among trimester exposures, and how effects may differ by race or socio-economic status.


Examples From Our Work


Increase in CVD hospitalizations per 10 µg/m3 increase in PM2.5 (Bell et al. American Journal of Respiratory and Critical Care Medicine 2009).


Temporal variation in particulate risk for CVD hospitalizations (Bell et al. American Journal of Epidemiology 2008).


Selected Relevant Publications

Bell ML, Peng RD, Dominici F, Samet JM. 2009. Emergency hospital admissions for cardiovascular diseases and ambient levels of carbon monoxide: results for 126 U.S. urban counties, 1999-2005. Circulation 120(11), p. 949-955.

Bell ML, Ebisu K, Peng RD, Walker J, Samet JM, Zeger SL, Dominici F. 2008. Seasonal and regional short-term effects of fine particles on hospital admissions in 202 U.S. counties, 1999-2005. American Journal of Epidemiology 168(11), p. 1301-1310.

Bell ML, Ebisu K, Belanger K. 2007. Ambient air pollution and low birth weight in Connecticut and Massachusetts. Environmental Health Perspectives 115(7), p. 1118-1124.

Bell ML, McDermott A, Zeger SL, Samet JM, F Dominici. 2004. Ozone and mortality in 95 U.S. urban communities, 1987 to 2000. Journal of the American Medical Association 292(19), p. 2372-2378.

Bell ML, Davis DL. 2001. Reassessment of the lethal London Fog of 1952: novel indicators of acute and chronic consequences of acute exposure to air pollution. Environmental Health Perspectives 19 (Suppl 3), p. 389-394.