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The Air Pollution Index is a way of describing the concentration of air
pollutants. If the concentration of a pollutant exceeds the national
standard, the index moves from 'Low' to 'Moderate'. Increased concentrations
lead to levels reaching 'High' or exceptionally 'Very High'. In recent years
'very high' episodes have been confined to a very few days when PM10 particle
concentrations became elevated.
Air Pollution Index
for PM10 particles
The graph opposite shows a summary of the PM10 (fine particle)
pollution level in Leeds over the last two days until the present. The graph
shows a running 24 hour average of results (The standard is a daily average)
and normally is calculated from Leeds Centre station a background site
reflecting long term exposure, at present due to a fault it is the Headingley data that is displayed a kerbside site likely
to be giving higher values.
These particles are
produced by a wide variety of sources notably road transport and other
combustion sources but can also occur as a result of chemical reactions of
other pollutants in the atmosphere.
Air pollution index
for SO2
The graph opposite shows a summary of the sulphur dioxide levels measured in
Leeds. over the last two days until the present. The graph displays 15 minute
values obtained from the Leeds Centre station.
Concentrations of sulphur
dioxide are very low nowadays due to improvements in cleaning the emissions from
the coal fired power stations in the Aire valley. It is unlikely that moderate concentrations
would be recorded
Air pollution index
for NO2
The graph opposite shows a summary of the nitrogen dioxide levels measured in
Leeds and the surrounding area over the last two days until the present. The
graph shows the highest of the hourly values obtained from four monitoring
stations - Leeds Centre, Kirkstall Road, Haslewood
Close, and Jack Lane.
The main source of
nitrogen dioxide affecting the City Centre is road traffic. Most of the
monitoring stations have been located alongside some of the busiest roads in
Leeds to establish whether the short term (hourly) air quality objectives are
exceeded in places where people may breathe that air for that length of time.
Air Pollution Index
for O3
The graph opposite shows a summary of the ozone pollution level in Leeds over
the last two days until the present. The graph shows a running 8 hour average
of results (the way the national standard is calculated) and has been
obtained from the Leeds Centre monitoring station. Although an air quality
standard exists for this pollutant, it is widely accepted that its occurrence
is beyond the control of individual local authorities.
Ozone is created by the
action of sunlight on other pollutants which can arrive in this country by transboundary migration from the continent.
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