Automatic monitoring equipment should have an independent verification of performance, such as the Environment AgencyÃ¢ÂÂs MCERTS scheme.
There are is a wide range of sampling and detection methods available depending on the pollutant being measured, some of the main techniques for particulate matter are indicated below:
Automatic real-time point analyser methods
Provide high-resolution measurements (typically hourly or shorter time periods). In order to ensure that data is accurate and reliable, there needs to be a high standard of maintenance, calibration and QA/QC procedures in place. These types of monitors can measure different particulate fractions such as PM10 and PM2.5 when fitted with designated inlet heads. Monitors such as TEOM or beta-attenuation analysers (with heated inlets) need to be corrected when comparing results with the AQS objectives, as these are based on a gravimetric standard.
This monitoring method is considered to be the most accurate and produces concentrations equivalent to the EU reference samplers, which are used to set EU limit values. Such systems have designated inlet heads to measure different particulate fractions and a typical measurement is taken over 24 hours. The measurement system is time-consuming as filters need to be individually weighed and accurate filter weighing and conditioning facilities are required. This method cannot be used as a trigger system as it does not produce instantaneous readings and is there unsuitable for use in construction monitoring.
Remote optical indicative monitors
These are relatively low-cost automatic analysers that have been developed specifically for portable or personal exposure applications. These tend to be battery or mains powered and use the light scattering principle to measure PM10 and other particulate fractions. These Ã¢ÂÂindicativeÃ¢ÂÂ monitors are most commonly deployed around construction site due to their affordability and ease of installation.
Although these types of monitors are not as accurate as automatic monitors and cannot be used for long term studies, they are ideal for walk-over surveys of construction sites as they provide real time or instantaneous dust readings (every second). These monitors can be set up to measure different particle sizes and can be used to assess short term peaks and breaches of set limits
Black carbon monitors
A large percentage of the particulate from MRMM engine emissions are PM1 and smaller and are not detected accurately by any of the above methods. These are normally recorded using an aetholometer which is an instrument that uses optical analysis to determine the mass concentration of Black Carbon particles collected from an air stream passing through a filter. These particles are directly emitted to the air during all combustion, but are primarly associated with coal or diesel smoke. They adversely affect public health and are known to be carcinogenic.
Approaches to measure the amount of dust deposited on a surface tend to focus on either determining the soiling of a surface by a change in its properties or determining the quantity of dust deposited, by weight.
These techniques are often used to determine nuisance and include Deposit gauges. These are simple, but accurate methods to measure nuisance dust. Dust is collected onto a horizontally mounted capture container, or, in the case of a Directional Dust Gauge, into four vertical tubes aligned in different directions. The dust collected can also be analysed to determine its composition.