Monitoring Air Pollution

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

Method	Advantages	Disadvantages
Passive Samping	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 portably.	Low sensitivity may only provide spot measurements.
Active (semi-automatic) sampling	Low cost - easy to operate - reliable. Historical datasets 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 Locations

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

Type	Description	Source Influences	Objectives
RURAL	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'.
URBAN	URBAN	Vehicle, commercial, space heating.	Identification of long-term urban trends.
KERBSIDE	A site sampling within 1m of the kerb 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.
REMOTE	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.
ROADSIDE	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.
SUBURBAN	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.
INTERMEDIATE	20-30m from the kerb of a busy road	Vehicle, commercial, space heating.	Identification of long-term urban trends.
AIRPORT	Monitoring within the boundary of an airport perimeter.	Aircraft, vehicle, commercial, space heating.	Determine air quality impact of airport.
OTHER	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.