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Air monitoring methodologies can be divided into five main types, covering a wide range of costs and performance levels. The methods and their relative merits are shown in the table below and discussed in the following section. The use of a particular type of monitoring equipment may need to be justified in review and assessment reports and therefore should be chosen appropriately.

It is also important to choose the most appropriate monitoring location for investigating a specific air pollution source or problem.

Advantages and Disadvantages of Monitoring Methods

Please click the method links to view detailed description of the method.

Method Advantages Disadvantages
Passive sampling Low cost - simple. Useful for screening and base-line studies and in support of automatic monitoring for Detailed Assessments. Unproven for some pollutants. Laboratory analysis required. In general, only provide weekly or longer averages.
Photochemical and optical sensor systems Can be used portable. Low sensitivity may only provide spot measurements.
Active (semi-automatic) sampling Low cost - easy to operate - reliable. Historical data sets available from UK networks. Provide daily averages. Some methods are labour intensive. Laboratory analysis required.
Automatic point monitoring Provide high resolution data. On-line data collection possible. Provide path or range-resolved data. Relatively expensive. Trained operator required. Regular service and maintenance costs.
Remote optical/long-path monitoring Useful near sources. Multi-component measurements possible. Relatively expensive. Trained operator required. Data not readily comparable with point measurements.

Since monitoring instrumentation covers a wide range in capital and running costs, it is usually advisable to choose the simplest method available to meet the specified monitoring objectives. Many baseline monitoring, spatial screening and indicative surveys can be served perfectly well by inexpensive active or passive sampling methods. Only proven and generally accepted measurement methods should be considered.

Monitoring site locations

Monitoring sites can be classified according to the type of environment in which they are located, in order to permit more meaningful evaluation of data. The site description will generally reflect the influence of a particular pollutant source or of overall land use. Typical monitoring location types, as used in national automatic monitoring networks, are described in the table below.

Description Source Objectives
Urban Vehicle, commercial, space heating. Identification of long-term urban trends
A site sampling within 1m of the kerbside of a busy road. Local traffic. Identifying vehicle pollution blackspots. Assessing worst case scenarios. Evaluating impacts of vehicle emission control technologies. Determining impacts of traffic planning/calming schemes.
A site sampling between 1m of the kerbside of a busy road and the back of the pavement. Typically this will be within 5m of the road, but could be up to 15m. Local traffic. Assessing worst case population exposure.Evaluating impacts of vehicle emission controls.Determining impacts of traffic planning/calming schemes.
A location type situated in a residential area on the outskirts of a town or city. Traffic, commercial, space heating, regionaltransport, urban plume downwind of a city. Traffic and land-use planning.Investigating urban plumes.
Urban Background
An urban location distanced from sources and therefore broadly representative of city-wide background conditions e.g. urban residential areas. Vehicle, commercial, space heating. Trend analysis.Urban planning.Traffic and land-use planning.
Urban Centre
An urban location representative of typical population exposure in towns or city centres e.g. pedestrian precincts and shopping areas. Vehicle, commercial, space heating. Identification of long-term urban trends.
Urban Industrial
An area where industrial sources make an important contribution to the total pollution burden. Intermediate. 20-30m from the kerb of a busy road. Industrial, motor vehicles. Assessing local impacts on health and amenity. Process optimization. Source attribution/identification. Providing model input data. Model development/validation. Local planning and plant authorization.
20-30m from the kerb of a busy road. Vehicle, commercial, space heating. Identification of long-term urban trends.
Monitoring within the boundary of an airport perimeter. Aircraft, vehicle, commercial, space heating. Determine air quality impact of airport.
Any special source-orientated or location category covering monitoring undertaken in relation to specific emission sources such as power stations, car parks or tunnels. As specified. As specified.
An open countryside location, in an area of low population density distanced as far as possible from roads, populated and industrial areas. Regional long-range transport, urban plume. Ecosystem impact studies.Assessing compliance with critical loads and levels for crops and vegetation.Investigating regional and long-range transport.Identification of ozone hot spots.
A site in open country, located in an isolated rural area, experiencing regional background pollutant concentrations for much of the time. Regional/hemispheric background. Assessing unpolluted global or hemispheric background conditions.Long-range transport studies. Long-term baseline trend analysis.