This is one of the most dangerous gases to
human health.
It is formed by the conversion of nitrogen monoxide (NO) in
oxygen or ozone to form nitrogen dioxide (NO2).
NO2 is an irritant with the ability to increase
sensitivity to allergens at low levels with evidence that
exposure can increase the risk of childhood respiratory
infections.
It has also been shown that it can impair lung functions in
later life.
Asthmatics and those suffering from emphysema and other breathing
problems are thought to be especially sensitive to atmospheric
NO2 levels.
Motor vehicles contribute around half and power stations
a quarter of the NO2 levels found in our
air.
Domestic heating is also a significant source in urban areas
where NO2 peaks during the day's two rush-hour
periods.
The highest concentrations are generally found on cold days with
low wind speeds when the cold air traps the
NO2 at ground level.
In North Somerset we measure NO2 levels through
diffusion tubes which consist of open tubes with a pollutant
absorbing gel at one end.
They can be used to measure the average levels of pollutants but
are unable to measure peak values.
However, the relative cheapness of this method allows us to
currently sample levels at 40 sites.
