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Monitoring methods


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

The monitoring site locations within the Heathrow Airwatch network used to define where air quality is measured are defined below.


Description Source Objectives
Monitoring within the boundary of an airport perimeter. Aircraft, vehicle, commercial, space heating. Determine air quality impact of airport.


Description Source Objectives
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.


Description Source Objectives
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

Description Source Objectives
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

Description Source Objectives
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.