Monitoring Techniques
Air quality monitoring in Carlisle City Council is driven by the
local air quality management process and in particular the review
and assessment of air quality. At present Carlisle City Council
monitors for 3 pollutants i.e nitrogen dioxide, particulates
and benzene.
We monitor pollution levels using a number of different
techniques and instruments. Some of these are very basic pieces of
equipment, while others are state of the art equipment that use
complex electronic systems and computer technology to provide up to
the minute information on pollution levels. These include:
Diffusion Tubes
A diffusion tube is a simple and
relatively inexpensive device consisting of a plastic tube which
can be attached to street furniture (e.g. a street light) allowing
a sample of air to be collected (over a recorded exposure period)
by diffusion into the sampler. The tubes are sealed and then sent
off for quantitative analysis. They give a good general indication
of average pollutant levels.
Automatic Monitoring Stations
These stations consist of a permanent housing, such as a
portacabin, which contains a number of sophisticated electronic
instruments. Air is continuously pumped into each analyser and the
level of the pollutant in the air recorded.
The pollution levels are automatically stored by the analyser and
the data sent via telephone lines to a central computer where data
is collected. The analysers are 'calibrated' every two weeks to
make sure they are working correctly . This is done by putting a
sample of air containing a known level of the pollutant into the
analyser and making sure the analyser reads the same level.
Carlisle has two automatic monitoring stations at:
Caldewgate
View
data from the Caldewgate Monitoring Unit (external link)
This station opened in 2005 following the floods. It is a
roadside site located adjacent to the A595 in Caldewgate. It
measures both nitrogen dioxide and particulates. The site was
affiliated to the automatic urban and rural network in February
this year. This means that this site will provide high quality data
to the network that will be used by Defra to:
- determine compliance with EC Directives
- analysis and forecasting of air pollution episodes
- examine long term trends in UK air pollution
- input into national air quality modelling for UK status.
Stanwix Bank
Monitoring
Unit
This station opened at the beginning of 2007. It is close to the
roadside located adjacent to the A7 Stanwix Bank, within AQMA No 1.
It measures nitrogen dioxide. Results from this unit can be found
at www.air-quality.net (external
link)