EFFECTS OF AIR POLLUTION MEASURED BY VISIBILITY ON MORTALITY IN HONG KONG

ABSTRACT

There seems to be a consensus among most people that visibility impairment is the most obvious indicator of the presence of pollution in the atmosphere. While considerable evidence on the association between air pollution and health outcomes including death has been established, based on high-pollution episodes, time series analyses and cohort studies, scarce literature exists on the direct evidence for the association between visibility and adverse health outcomes. We assessed the effect of air pollution measured by visibility impairment on mortality over a period of three years. Relative risks in deaths were estimated by a Poisson regression model of daily deaths between 2000-03. Daily counts of mortality, due to all natural causes, respiratory and cardiovascular diseases as dependent variable were modelled with daily 24-hr mean (airport) visibility measurements (kilometers) as independent variable by means of Poisson regression. We controlled for confounding factors such as climatotogic, holidays, influenza and seasonal variables and an interaction term for season and visibility by fitting the terms in the model similar to that for modelling mortality on pollutant concentrations. We observed an inverse health effect with visibility during the cool season for all-cause mortality (relative risk for all ages 1.03 95% CI 1.00-1.07; for age 45⁺ 1.04 95% CI 1.01-1.07; for age 65⁺ 1.05 95% CI 1.02-1.09 per 10 km decreased in visibility); and for respiratory mortality (corresponding relative risks 1.08 95% CI 1.00-1.16; 1.08 95% CI 1.00-1.16; 1.07 95% CI 0.99-1.16). The effect was much reduced during warm season. Visibility impairment resulting from pollution is strongly associated with mortality, especially for all causes and respiratory diseases. It provides a quick and useful indicator for eliciting the contribution of pollution to the excess risk of mortality in Hong Kong.