Air Quality Guidelines Global Update 2005 - World Health ...

402
AIR QUALITY GUIDELINES
discussion that follows focuses on those studies that were unaffected or have
been re-analysed.
In the following sections, short-term and long-term effects will be considered
separately.
Short-term effects
In the past ten years, there have been nearly 200 mortality and morbidity time
series studies that examined short-term impacts of PM, and about 60% of these
studies also examined the impacts of sulfur dioxide. There have also been several
multi-city studies of mortality and morbidity in Canada, Europe and the United
States that also examined sulfur dioxide. These multi-city studies have advantages
over a collection of single-city studies because they analyse data from many
cities using consistent methodology and attempt to explain variations in the
risk estimate using city characteristics (e.g. differences in weather, poverty, etc.).
Therefore, this discussion focuses on the results from the multi-city studies.
Mortality studies
A series of studies from the Air Pollution and Health: A European Approach
(APHEA) project examined mortality effects of air pollution in several cities.
The APHEA 1 project (17) reported total non-accidental mortality risk estimates
for sulfur dioxide and PM in 12 European cities, noting that the effects
of these two pollutants were “mutually independent” and were stronger during
the summer. The observed associations were stronger in western European cities
than in central and eastern European cities (Table 1). The median levels of sulfur
dioxide in these 12 cities ranged from 13 μg/m 3 (Bratislava) to 74 μg/m 3 (Cracow).
An examination of cause-specific mortality in a subset of 10 of the above
12 cities found that estimated risks were larger for cardiovascular and respiratory
categories than those for total non-accidental mortality (18). Samoli et al.
(19,20) applied an alternative model (a more flexible smoothing model to adjust
for seasonal cycles) to the 12 cities data and also conducted subset analyses for
moderate sulfur dioxide levels (