Daily visibility and mortality: assessment of health benefits from improving visibility in Hong Kong

Abstract

Background/Aims: Visibility in Hong Kong has deteriorated significantly over 40 years with the frequency of visibility below 8 km in the absence of fog, mist, or precipitation, increasing from 6.6 days in 1968 to 54.1 days in 2007.

Methods: During 1996–2006, we obtained mortality data for all natural and cardiorespiratory causes, visibility recorded as visual range in kilometers, temperature and relative humidity from an urban observatory, and concentrations of 4 criteria pollutants. A generalized additive Poisson regression model with penalized cubic regression splines was fitted to control for time–varying covariates.

Results: For all natural causes of mortality an interquartile range of 6.5 km increase in visibility at lag 0–1 days was associated with an excess risk (ER%) (95% Confidence Interval) of -1.13 [-1.76, -0.49] for all ages and -1.37 [-2.09, -0.65] for ages 65+; for cardiovascular mortality of -1.31 [-2.49, -0.13] for all ages, and -1.72 [-3.00, -0.44] for ages 65+; for respiratory mortality of -1.92 [-3.35, -0.49] for all ages and -1.76 [-3.25, -0.28] for ages 65+. The estimated ER% for daily mortality derived from both visibility and air pollutant data were comparable in terms of magnitude, lag pattern, and dose-response relationships especially when using particulate matter with aerodynamic diameter <=10 µm to predict mortality associated with visibility.

Conclusion: Visibility provides a useful proxy for the assessment of environmental health risks from ambient air pollutants and a valid approach for the assessment of the public health impacts of air pollution and the benefits of air quality improvement measures in developing countries where pollutant monitoring data are scarce.