I know this can't be plugged into a computer, but you could make it
yourself for free :)
found this at http://www.enviropedia.org.uk/Air_Quality/Measuring.php
"Measuring Air Quality
There are many ways to measure air pollution, with both simple
chemical and physical methods and with more sophisticated electronic
techniques. There are four main methods of measuring air pollution.
Passive sampling methods provide reliable, cost-effective air quality
analysis, which gives a good indication of average pollution
concentrations over a period of weeks or months. Passive samplers are
so-called because the device does not involve any pumping. Instead the
flow of air is controlled by a physical process, such as diffusion.
Diffusion tubes are simple passive samplers, which provide very useful
information regarding ambient air quality. They are available for a
number of pollutants, but are most commonly and reliably used for
nitrogen dioxide and benzene. The tubes, which are 71mm long with an
internal diameter of 11mm, contain two stainless steel gauzes placed
at one end of a short cylinder. The steel gauzes contain a coating of
triethanolamine, which converts the nitrogen dioxide to nitrite. The
accumulating nitrates are trapped within the steel gauze, ready for
laboratory analysis. The tube is open to the atmosphere at the other
end, which is exposed downwards to prevent rain or dust from entering
the tube. To ensure that all the nitrogen dioxide originates from the
test site, the tubes are sealed before and after exposure. The tubes
are manually distributed and collected, and are analysed in a
laboratory.
Active sampling methods use physical or chemical methods to collect
polluted air, and analysis is carried out later in the laboratory.
Typically, a known volume of air is pumped through a collector (such
as a filter, or a chemical solution) for a known period of time. The
collector is later removed for analysis. Samples can be collected
daily, providing measurements for short time periods, but at a lower
cost than automatic monitoring methods.
Automatic methods produce high-resolution measurements of hourly
pollutant concentrations or better, at a single point. Pollutants
analysed include ozone, nitrogen oxides, sulphur dioxide, carbon
monoxide and particulates. The samples are analysed using a variety of
methods including spectroscopy and gas. The sample, once analysed is
downloaded in real-time, providing very accurate information.
Remote optical / long path-analysers use spectroscopic techniques,
make real-time measurements of the concentrations of a range of
pollutants including nitrogen dioxide and sulphur dioxide.
The amount of pollution in the air, however sampled, is usually
measured by its concentration in air. The concentration of a pollutant
in air may be defined in terms of the proportion of the total volume
that it accounts for. Concentrations of pollutant gases in the
atmosphere are usually measured in parts per million by volume (ppmv),
parts per billion by volume (ppbv) or parts per trillion (million
million) by volume (pptv). Pollutant concentrations are also measured
by the weight of pollutant within a standard volume of air, for
example microgrammes per cubic metre (µgm-3) or milligrammes per cubic
metre (mgm-3)." |
