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

NITROGEN DIOXIDE
nitrogen dioxide effect seemed to be different in boys and girls. In boys, nitrogen
dioxide showed no significant effect until three days of accumulated exposure,
and seemed to increase slightly with number of days of exposure up to an average
of six days. In girls, only seven-day exposure averages consistently showed a
significant effect on asthma hospital admissions. The effect estimates at six-day
cumulative lag were increases of 12% (1–23%) in boys and 16% (2–31%) in girls
per 11 ppb increase in nitrogen dioxide. The effect for nitrogen dioxide did not
change after adjusting for coarse PM.
Daily air pollution levels and daily respiratory hospital admissions in children
(three age groups: 0, 1–4 and 5–14 years) for five cities in Australia and two cities
in New Zealand were analysed using city-specific case-crossover methods
and pooling the results with meta-analysis (135). Levels of air pollution in these
countries were generally lower than in other locations studied in Europe and the
United States. All respiratory admissions, asthma, and pneumonia plus acute
bronchitis were considered. The mean 24-hour nitrogen dioxide concentration
ranged from 7.0 ppb to 11.7 ppb and the nitrogen dioxide–PM2.5 correlation was
from 0.34 to 0.68. In the 1–4-year age group, both PM2.5 and nitrogen dioxide
were associated with total respiratory admissions, the largest effect found being
for nitrogen dioxide (2.8% increase per 9.0 ppb 1-hour nitrogen dioxide, 95%
CI 0.7–4.9); in 5–14-year-olds, an association was found with PM10 and nitrogen
dioxide, again with the strongest effect for nitrogen dioxide (5.8% per 5.1 ppb
24-hour nitrogen dioxide, 95% CI 1.7–10.1). In general, the largest association
found was a 6% (95% CI 0.2–12.1) increase in asthma admissions related to an
interquartile range (5.1 ppb) increase in 24-hour nitrogen dioxide. A matching
technique (control days) was used to evaluate the effect of a pollutant while controlling
for the effect of another. In the 1–4-year age group, controlling for PM10
attenuated the effect of nitrogen dioxide to a non-significant value, whereas in
the 5–14-year age group, controlling for PM10 did not affect the results for nitrogen
dioxide while the effect of PM10 was sensitive to the effect of nitrogen dioxide.
The impact of nitrogen dioxide was stronger in warmer cities and during the
summer.
Finally, the study on emergency department visits in Atlanta (136) has been
mentioned, giving a relative risk of 1.027 (95% CI 1.005–1.050) per 20-ppb increase
in 1-hour nitrogen dioxide concentration for paediatric asthma (2–18
years).
In summary, a consistent association between air pollution and hospital admissions,
emergency department visits and visits to the doctor for asthma in children
has been found in epidemiological studies. Most of the studies indicated an
effect of PM and ozone. In many of the recent studies, however, nitrogen dioxide
was strongly related to hospital admissions or emergency department visits for
asthma, and there are several instances when nitrogen dioxide was the only pollutant
associated with health effects or where the effect remained after adjusting
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