ABSTRACT:
There have been many time series and case
-
crossover (CCO) studies of short
-
term
ambient air pollution effects on daily mortality and morbidity. To the best of our knowle
dge, no
CCO studies of such effects in Thailand have been published previously. We conducted a CCO
study to assess effects of ambient air pollution on non
-
external (non
-
accidental) mortality in
Bangkok during 1999
-
2001 (total 3 years). We assessed associat
ions of daily non
-
external
mortality with ambient air pollutant concentrations in Bangkok from 1999 through 2001.
Pollutant metrics assessed were 24
-
hour average particulate matter of diameter ≤10 μm (PM
10
),
nitrogen dioxide (NO
2
), and sulfur dioxide (SO
2
), and 8
-
hour average ozone (O
3
) from 10:00 AM
to 6:00 PM. Data were analyzed with stratified conditional logistic regression. There was one
stratum for each of the 102,522 deaths included in analysis. In each stratum, the case day was the
day on which a g
iven death occurred. The crossover (control) days were all matched days of week
in the same month as the case day (time
-
stratified analysis). Two
-
day moving average levels of
each pollutant were assessed in separate analyses (single
-
pollutant models). For
each pollutant,
unadjusted effects and effects adjusted for same
-
day average temperature and previous
-
day
average relative humidity, were modeled. Air pollution effects were assessed overall, by year, and
by gender. The study revealed that pollutant concen
trations were consistently positively
associated with mortality from non
-
external causes. Unadjusted associations were statistically
significant (p<0.05) for O
3
, SO
2
, and PM
10
. Adjusted associations were significant for NO
2
and
PM
10
. Adjusted pollutant eff
ects were weaker than unadjusted ones for all pollutants but NO
2
.
Associations of air pollution with mortality varied considerably by year, and were generally
strongest in 2001. Associations were significantly stronger in females than males. Conclusions,
t
hese findings suggest that in Bangkok, daily non
-
external mortality increases with increasing
short
-
term exposure to ambient air pollution, especially PM
10
. Findings are qualitatively
consistent with those of previous studies of air pollution and daily mor
tality. Further research is
needed to develop optimal strategies for adjusting analytical models for weather, to evaluate the
generalizability of these findings across times and across locations in Asia, to advance
understanding of observed temporal and ge
nder differences in air pollution effects, and to assess
the relative importance of different pollutants (e.g., airborne particulate and gaseous pollutants) in
promoting increased mortality.
Keywords:
ambient air pollution, non
-
external mortality,
case
-
crossover, Bangkok
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