Seasonal and temperature modifications of the association between fine particulate air pollution and cardiovascular hospitalization in New York state.

It is known that extreme temperature and ambient air pollution are each independently associated with human health outcomes. However, findings from the few studies that have examined modified effects by seasons and the interaction between air pollution and temperature on health endpoints are inconsistent. This study examines the effects of short-term PM2.5 (particulate matter less than or equal to 2.5μm in aerodynamic diameter) on hospitalization for cardiovascular diseases (CVDs), its modifications by season and temperature, and whether these effects are heterogeneous across different regions in New York State (NYS). We used daily average temperature and PM2.5 concentrations as exposure indicators and performed a time series analysis with a quasi-Poisson model, controlling for possible confounders, such as time-relevant variables and dew point, for CVDs in NYS, 1991-2006. Stratification parametric models were applied to evaluate the modifying effects by seasons and temperature. Across the whole year, a 10-μg/m3 increment in PM2.5 concentration accounted for a 1.37% increase in CVDs (95% confidence interval (CI): 0.90%, 1.84%) in New York City, Long Island & Hudson. The PM2.5 effect was strongest in winter, with an additional 2.06% (95% CI: 1.33%, 2.80%) increase in CVDs observed per 10-μg/m3 increment in PM2.5. Temperature modified the PM2.5 effects on CVDs, and these modifications by temperature on PM2.5 effects on CVDs were found at low temperature days. These associations were heterogeneous across four PM2.5 concentration regions. PM2.5 was positively associated with CVD hospitalizations. The short-term PM2.5 effect varied with season and temperature levels, and stronger effects were observed in winter and at low temperature days.