Short-term Effects of Particulate Matter Pollutants on Population Health - Time Series Studies on Emergency Hospital Admissions

BACKGROUND: The adverse effects of particulate matter (PM) air pollution have been confirmed by many epidemiological studies. Fine and coarse particles should be considered as separate classes of pollutants and measured separately. Differentiating the effects of fine (PM2.5, particles with an aerodynamic diameter less than 2.5 microns) and coarse particles (PMc, particles with an aerodynamic diameter between 2.5 and 10 microns) would help in the future to support a PMc standard. Meanwhile, ambient air pollution is a complex mixture of PM and gaseous pollutants. PM might interact with gaseous pollutants to affect the population health.;STUDY OBJECTIVES: To differentiate the effects of fine and coarse fractions of PM10 and to explore the possible interaction between PM10 and gaseous pollutants (nitrogen dioxide, NO 2; sulfur dioxide, SO2; ozone, O3) on emergency hospital admissions for cardio-respiratory diseases in Hong Kong.;METHODS: This is a time series study. Daily counts of emergency hospital admissions for cardio-respiratory diseases, daily mean air pollution concentrations and weather conditions were collected from January 1998 to December 2007 in Hong Kong. We used generalized additive Poisson model with log link allowing overdispersion and autocorrelation to examine the differential effects of PM2.5 and PMc. Three parallel time series approaches (bivariate response surface model, joint effect model and parametric stratified model) were used to explore the possible interactions between PM 10 and gaseous pollutants.;MAIN RESULTS: The associations between PMc and emergency hospital admissions were statistically significant for respiratory diseases but not for circulatory diseases. In two-pollutant (PM2.5 and PMc) model, an interquartile range increase in the 4-day moving average (lag03) concentrations of PMc and PM2.5 corresponded to 1.05% (95% CI: 0.19%, 1.91%) and 1.81% (95% CI: 0.76%, 2.87%) increase of respiratory admissions, respectively. The effect estimates of PM2.5 and PMc remained robust when adjusting for gaseous pollutants. Meanwhile, an interquartile range increase in lag 01 concentrations of PMc and PM2.5 was associated with -0.16% (95% CI: -1.07%, 0.76%) and 1.86% (95% CI: 0.85%, 2.88%) change of circulatory admissions, respectively. Some interactions between PM 10 and gaseous pollutants were found. The effects of PM10 on circulatory hospitalizations were greatest during the days when NO 2 or SO2 concentrations were high (the 3rd tertile, NO2>64.4 or SO2>20.9microg/m3). The effects of PM10 on both respiratory and circulatory admissions were greatest during the days when O3 concentrations were in low to medium levels (<=46.8microg/m3).;CONCLUSION: We found PMc to be associated with emergency hospital admissions for respiratory diseases independent of the effect of PM2.5, but not for circulatory diseases in Hong Kong. The effects of PM10 on cardio-respiratory hospital admissions were modified by gaseous pollutants. There were synergetic interactions between PM10 and NO2 or SO2 on cardiac hospitalizations and antagonistic interactions between PM10 and ozone on cardio-respiratory hospitalizations. These findings provide supportive evidence for a future PMc regulation and contribute to the development of a multipollutant air quality management.