4. Discussion
Emergency visits for asthma increased with increased
annual levels of 3 related pollutants (CO, NO2, and PM10)
in children but not for any pollutants in adults in the
present study.
Diesel- and gasoline-powered vehicular engines and coaland
oil-fired power plants are the main sources of ambient
NO2 emissions, which typically result from the fixation of
nitrogen in the air during high-temperature combustion [9].
Several studies have shown that NO2 is a risk factor for
exacerbation of asthma in children. The risks of respiratory
tract symptoms were associated with increased ambient NO2
in London and Japan [10,11].