Epidemiological findings concerning the seasonal variation in the acute effect of particulate matter (PM) are inconsistent.
We investigated the seasonality in the association between PMwith an aerodynamic diameter of less
than 10 μm(PM10) and dailymortality in 17 Chinese cities. We fitted the “main” time-seriesmodel after adjustment
for time-varying confounders using smooth functions with natural splines. We established a “seasonal”
model to obtain the season-specific effect estimates of PM10, and a “harmonic” model to show the seasonal pattern
that allows PM10 effects to vary smoothlywith the day in a year. At the national level, a 10 μg/m3 increase in
the two-day moving average concentrations (lag 01) of PM10 was associated with 0.45% [95% posterior interval
(PI), 0.15% to 0.76%], 0.17% (95% PI,−0.09% to 0.43%), 0.55% (95% PI, 0.15% to 0.96%) and 0.25% (95%PI,−0.05% to
0.56%) increases in total mortality for winter, spring, summer and fall, respectively. For the smoothly-varying
plots of seasonality, we identified a two-peak pattern in winter and summer. The observed seasonal pattern
was generally insensitive tomodel specifications. Our analyses suggest that the acute effect of particulate air pollution
could vary by seasonswith the largest effect inwinter and summer in China. To our knowledge, this is the
first multicity study in developing countries to analyze the seasonal variations of PM-related health effects.
Epidemiological findings concerning the seasonal variation in the acute effect of particulate matter (PM) are inconsistent.We investigated the seasonality in the association between PMwith an aerodynamic diameter of lessthan 10 μm(PM10) and dailymortality in 17 Chinese cities. We fitted the “main” time-seriesmodel after adjustmentfor time-varying confounders using smooth functions with natural splines. We established a “seasonal”model to obtain the season-specific effect estimates of PM10, and a “harmonic” model to show the seasonal patternthat allows PM10 effects to vary smoothlywith the day in a year. At the national level, a 10 μg/m3 increase inthe two-day moving average concentrations (lag 01) of PM10 was associated with 0.45% [95% posterior interval(PI), 0.15% to 0.76%], 0.17% (95% PI,−0.09% to 0.43%), 0.55% (95% PI, 0.15% to 0.96%) and 0.25% (95%PI,−0.05% to0.56%) increases in total mortality for winter, spring, summer and fall, respectively. For the smoothly-varyingplots of seasonality, we identified a two-peak pattern in winter and summer. The observed seasonal patternwas generally insensitive tomodel specifications. Our analyses suggest that the acute effect of particulate air pollutioncould vary by seasonswith the largest effect inwinter and summer in China. To our knowledge, this is thefirst multicity study in developing countries to analyze the seasonal variations of PM-related health effects.
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