There is a plethora of techniques and instrumentation available for undertaking
this monitoring, the most common of which are outlined in the table below:
| Instrument /Technique
|
Description |
| Deposit Gauges |
Many have been developed to undertake
long-term assessment and identify long-term trends of deposited
matter. They are not of great value as collectors and also will
collect rain and snow which undoubtedly impedes results. Types:
British Standard Deposit Gauge; ISO Deposit Gauge; CERL Deposit
Gauge. |
| Gas Detection Tubes |
These measure and detect particular
atmospheric gases. Many tubes have been produced to measure specific
gases or a range of specific gases. Gas of a known volume is passed
through a hand held device- the concentration is measured by the amount
of colour change undergone by sensitised crystals in the device and
volume of gas tested. This equipment is rugged and reliable- should the
tube be well maintained and calibrated. This is mainly the only
technique that is readily available for surveys.
Diffusion tubes can also be used which assess gases through
adsorption. These are left to take measurements over longer periods
than the tubes mentioned above- and enable detailed investigation of
certain gases without the expense- these are often used for large scale
investigations such as pollutants over cities. |
| Simple Collectors of Deposited Matter |
Particulate matter can be collected by:
petri-dishes; greased glass plates; adhesive plastic sheets; plastic
washing up bowls etc. These allow simple observations to be made
between masses of particulates collected at different locations. |
| Simple Smoke / Sulphur Dioxide
Assessment |
This can be undertaken using: a daily
volumetric instrument (operates for a day at a time only); an eight
part volumetric instrument (can operate for a week); a Sequential
Particulate Sampler. |
| Cascade Impactors |
These characterise the size of particles
in the ambient air- a technique not often used within the UK.
Equipment: Modified Anderton Cascade Sampler. |
| High Volume Samplers |
Particulate matter is collected on a glass
fibre filter- the measurement is gravimetric and chemical analyses of
samples collected is possible. (A method used widely by the US
EPA). |
| Molecular Analysis Techniques. |
There are many of these techniques
available for the molecular analysis of gases, solids and liquids
collected during emissions monitoring, all of which would be undertaken
by an external laboratory (depending upon the nature and size of the
company). A summary of some of the techniques is given below:
- Gas chromatography- a qualitative method and widely used.
It doesn't reveal molecular weight or structure. Rugged and
reliable method of identifying pollutants.
- Electron microscopes: can be used on dusts and fibres.
- Emission spectrography- gives a qualitative determination of
metals to the smallest parts- the best method for
these purposes.
- Flame photometry- a quantitative method for determining
alkaline metals.
- Infrared spectroscopy- a quantitative method of analysing
liquid compounds.
- Mass spectroscopy- a quantitative method for determination
of the components of liquid and gas samples.
Others include: nuclear magnetic resonance; radiotracer techniques;
raman scattering; spectrophotometric; ultraviolet absorption;
ultraviolet fluorescence; x-ray absorption; x-ray diffraction; x-ray
fluorescence. |