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.

Air Quality

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• NETCEN

Passive sampling methods provide reliable, cost-effective air quality analysis,

• NETCEN

which gives a good indication of average pollution concentrations over a period

• Instrumentation

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,

Other topics such as diffusion. Diffusion tubes are simple passive samplers, which provide

• Introduction

very useful information regarding ambient air quality. They are available for a

• Asthma

number of pollutants, but are most commonly and reliably used for nitrogen

• Carbon Monoxide

dioxide and benzene. The tubes, which are 71mm long with an internal diameter

• Cars

of 11mm, contain two stainless steel gauzes placed at one end of a short

• CATs

cylinder. The steel gauzes contain a coating of triethanolamine, which converts

• Chemistry

the nitrogen dioxide to nitrite. The accumulating nitrates are trapped within the

• Cities

steel gauze, ready for laboratory analysis. The tube is open to the atmosphere

• Clean Air Acts

at the other end, which is exposed downwards to prevent rain or dust from

• Cleaner Fuels

entering the tube. To ensure that all the nitrogen dioxide originates from the

• Countryside

test site, the tubes are sealed before and after exposure. The tubes are

• Dispersion

manually distributed and collected, and are analysed in a laboratory.

• Doing Our Bit

• Dustmite

Active sampling methods use physical or chemical methods to collect polluted

• Emissions

air, and analysis is carried out later in the laboratory. Typically, a known volume

• Fossil Fuels

of air is pumped through a collector (such as a filter, or a chemical solution) for

• History

a known period of time. The collector is later removed for analysis. Samples can

• Human Health

be collected daily, providing measurements for short time periods, but at a

• Impacts

lower cost than automatic monitoring methods.

• Indoors

Automatic methods produce high-resolution measurements of hourly pollutant • Industry & Power concentrations or better, at a single point. Pollutants analysed include ozone, • Legislation nitrogen oxides, sulphur dioxide, carbon monoxide and particulates. The • Lichens

samples are analysed using a variety of methods including spectroscopy and • London Smog gas. The sample, once analysed is downloaded in real-time, providing very • Management accurate information. • Measuring

• Megacities

Remote optical / long path-analysers use spectroscopic techniques, make real- • Modelling

time measurements of the concentrations of a range of pollutants including • Monitoring nitrogen dioxide and sulphur dioxide. • Mould Spores

• Natural Sources

The amount of pollution in the air, however sampled, is usually measured by its • Nitrogen Dioxide concentration in air. The concentration of a pollutant in air may be defined in • Outdoors

terms of the proportion of the total volume that it accounts for. Concentrations • Ozone

of pollutant gases in the atmosphere are usually measured in parts per million • Particulates

by volume (ppmv), parts per billion by volume (ppbv) or parts per trillion • Pollutants (million million) by volume (pptv). Pollutant concentrations are also measured • Radon

by the weight of pollutant within a standard volume of air, for example • Smog

microgrammes per cubic metre (µgm-3) or milligrammes per cubic metre (mgm- • Smoke 3). • Smoking

• Standards

• Sulphur Dioxide

• UK Air Pollution

• UK Strategy

• Vehicle Controls

• VOCs

• Wildlife

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