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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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