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A STUDY OF SHORT-TERM EFFECTS
OF AMBIENT AIR POLLUTION ON PUBLIC HEALTH
A CONSULTANCY REPORT FOR
ENVIRONMENTAL PROTECTION DEPARTMENT HONG KONG
by
Dr. Wong Tze Wai
Professor *
(Principal Investigator)
Other Members of the Research Team:
THE CHINESE UNIVERSITY OF HONG KONG
September 1997
CONTENTS
EXECUTIVE SUMMARY
1.0 INTRODUCTION
2.0 SCOPE AND OBJECTIVES
3.0 STUDY HYPOTHESIS
4.0 MATERIALS AND METHODS
5.0 RESULTS
6.0 DISCUSSION
7.0 LIMITATIONS
8.0 DEVELOPMENT OF AN 'ACUTE HEALTH EFFECTS INDEX'
9.0 REFERENCES
APPENDIX 1
EXECUTIVE SUMMARY
This study represents an attempt to assess the acute disease burden due to ambient air pollution on the Hong Kong community through linking routinely collected hospital admission and environmental monitoring data. A times series approach was used covering the period between 1994 and 1995. The health outcomes under study were daily counts of hospital admissions for respiratory and cardiovascular diseases in 12 major hospitals under the Hospital Authority. Daily ambient concentrations of four air pollutants (nitrogen dioxide, sulphur dioxide, ozone and respirable suspended particulates) from seven air monitoring stations of the Environmental Protection Department were used as the primary independent variables. Meteorological variables were obtained from the Royal Observatory and, along with other variables, were used as covariates. A Poisson regression model, based on William's modified logistic linear model, was fitted, taking into account both linear and quadratic time trends, seasonality, days of the week and holiday effects. Significant associations were found between all four pollutants and hospital admissions for respiratory diseases, cardiovascular diseases, and bronchial asthma. Significant associations were found between ozone and hospital deaths due to respiratory and circulatory diseases, and between nitrogen dioxide and respiratory mortalities. These findings implied that exposure to these pollutants within the measured ranges were associated with a higher number of hospital admissions and mortalities due to these diseases. The magnitude of the risk varied between individual pollutants, ranging from a 13% (for sulphur dioxide) to 40% (for nitrogen dioxide) increase in hospital admissions for respiratory diseases, and a 13% (for ozone) to 18% (for sulphur dioxide) increase for cardiovascular diseases for every 100 ug.m-3 increase of pollutant level. The relative risks of deaths from respiratory and circulatory diseases for an increase in 100 ug.m-3 of ozone were 1.62 and 1.27 respectively, while that of respiratory mortalities for nitrogen dioxide was 1.31. Significant interactions were detected between nitrogen dioxide and ozone, and ozone and particulates. Infants, children and the elderlies were at higher risk of hospital admissions from the effects of the pollutants. The relative risks for all four air pollutants in this study are generally higher than those reported in the United States and Europe. The Poisson regression model was validated using data for the first half-year of 1996. The predicted daily hospital admissions were found to fit the observed pattern fairly well. Using the single pollutant model to quantify the health benefit, and assuming the associations between air pollutants and the measured health effects are causal, a reduction of 100 ug.m-3 of ambient ozone concentration would result in a 28% fall in hospital admissions for respiratory diseases and a 38% fall in respiratory mortalities. A similar reduction in nitrogen dioxide would lead to a 29% fall in hospital admissions for respiratory diseases and a 24% fall in respiratory mortalities.
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