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

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AIR QUALITY GUIDELINES
the few monitors. On the other hand, a greater spatial variability exists for nitrogen
dioxide, and it is therefore likely that daily variation in exposure to nitrogen
dioxide is less well-described than in the case of PM, resulting in a greater possibility
of misclassification.
Outdoor population-based studies: short-term effects
A large number of time series studies have used maximum hourly concentrations
and/or daily mean concentrations of nitrogen dioxide to evaluate a wide range of
short-term adverse health effects. The studies have been conducted at the population
level, including large cities in the world, or among subjects with pre-existing
chronic diseases such as asthmatics. Table 2 lists the results of selected studies
on short-term effects of nitrogen dioxide.
Time series studies on mortality
A meta-analysis of time series investigations on daily mortality, which incorporated
109 studies published between 1982 and 2000, with data from 1958–1999
(129), included 32 effect estimates for nitrogen dioxide from single-pollutant
models and 15 from multi-pollutant models. Over a 24-hour range of mean nitrogen
dioxide exposure (20.4–103.3 μg/m 3 ), the overall effect estimate from
the single-pollutant model for all-cause mortality was 2.8% (95% CI 2.1–3.5)
per 24 ppb nitrogen dioxide (24-hour), which fell to 0.9% (95% CI –0.1–2.0) in
multi-pollutant models, including particles. In single-pollutant models, the effect
estimate for nitrogen dioxide on respiratory deaths was higher (6.6 ± 1.6%),
whereas for cardiovascular deaths (3.2 ± 0.5%) it was similar to the value derived
for all-cause mortality. The conclusion of the meta-analysis did not change
when the methodological issues related to the use of generalized additive models
(GAM) for the data analysis were considered (137).
The results of multi-city studies conducted in Europe should be mentioned,
because the effect of nitrogen dioxide has been careful evaluated. The European
APHEA 1 study – the first European initiative on short-term health effects of
air pollution (138) – found a statistically significant effect of nitrogen dioxide on
daily mortality: a 1.3% increase in daily deaths (95% CI 0.9–1.8) per 50 μg/m 3
nitrogen dioxide (1-hour maximum) (139). The effect remained statistically significant
(0.6%, 95% CI 0–1.2) after adjusting for BS. The APHEA 2 study on daily
mortality in 29 cities (140) found that PM effects on daily mortality were stronger
in areas with high nitrogen dioxide levels. The overall estimated increase in the
daily number of deaths for all ages for a 10-μg/m 3 increase in daily PM10 was
0.6% (95% CI 0.4–0.8); in cities with low average nitrogen dioxide, however, the
estimated increase in daily mortality for the same-sized increase in PM10 was 0.19
(95% CI 0.00–0.41), whereas in a city with high average nitrogen dioxide it was
0.80% (95% CI 0.67–0.93). Finally, the APHEA 2 study reported, for nine European
cities, an increase of 2% in natural all-cause mortality per 50 μg/m 3 nitrogen