Air Quality Monitoring

Air Quality Monitoring Explained

Air quality monitoring is the ongoing measurement and analysis of pollutants in the atmosphere at a specific location over a defined period of time.

It records changes in air pollution levels as they occur, providing verifiable air quality data that can be used to demonstrate the environmental impact of a development, satisfy the requirements of a local planning authority and support the design of effective mitigation measures.

For development projects, monitoring is typically carried out across a minimum of three months, during which conditions on and around the site can change significantly.

Construction activity, plant and machinery, increased vehicle movements and changes to the surrounding road network can all affect local air quality, both temporarily during the build phase and on a longer-term basis once development is complete. Monitoring provides the evidence base to assess the effects of these changes and any air pollution episodes and respond to them.

We connect developers, housing providers and landowners with qualified air quality consultants who can carry out monitoring programmes and produce reports that meet the quality assurance standards required by local planning authorities across England, Scotland and Wales.

Air Quality Monitoring and the Planning Process

Air quality monitoring is one component of a broader air quality assessment, which may also include dispersion modelling, health impact analysis and the development of mitigation and management strategies.

The scope of monitoring required for any given project will depend on the scale and nature of the development, its location relative to sensitive receptors such as residential properties, schools, hospitals and care homes, and the existing baseline air quality in the surrounding area.

For larger or more complex developments, particularly those subject to an Environmental Impact Assessment (EIA), a detailed air quality chapter will be required as part of the Environmental Statement.

This will draw on baseline monitoring data collected over a sufficient period to characterise the existing conditions before construction begins, allowing the predicted effects of the development to be assessed against a verified starting point.

For smaller schemes, the monitoring requirement may be more limited, but even where a full air quality assessment is not required, the local planning authority may impose planning conditions requiring air quality monitoring to be carried out during the construction phase to ensure that agreed dust and emission controls are working effectively and that any target pollutant is managed correctly.

The key piece of national planning policy guidance on air quality is set out in the National Planning Policy Framework (NPPF), which requires planning decisions to contribute to improving air quality and to avoid placing development in locations where people would be exposed to unacceptable levels of pollution.

The NPPF is supported by Planning Practice Guidance on air quality, which provides detailed advice on the circumstances in which air quality assessments and monitoring are required and the air quality standards they should meet.

Why Does Air Quality Matter for Development?

Poor air quality affects the health of people living, working and travelling near a development site. The pollutants generated by construction and increased traffic can include fine particulate matter, nitrogen dioxide, heavy metals, carbon monoxide and a range of other substances that, at sufficient concentrations, pose risks to human health and the wider environment.

Industrial areas may be particularly affected by emission patterns in the atmospheric chemistry that could adversely affect human health and add to the amount of greenhouse gases being emitted into the atmosphere.

Local planning authorities are required to consider these impacts when assessing planning applications, and in areas where air quality is already under pressure, the scrutiny applied to development proposals is particularly close.

In England, local authorities are required to review and assess air quality and air pollutants in their areas under Part IV of the Environment Act 1995. Where they identify that national air quality objectives are not being met or are at risk of not being met, they must declare an Air Quality Management Area (AQMA) and produce an Air Quality Action Plan to address the problem.

Developments proposed within or close to an AQMA are subject to greater scrutiny, and applicants will typically be expected to provide robust monitoring data alongside any air quality assessment submitted with the planning application.

Beyond the planning process, poorly managed air quality during construction can result in complaints from neighbouring occupiers, enforcement action from the local authority and reputational damage to the developer. A structured monitoring programme, put in place from the outset of a project, provides both the data to manage these risks proactively via abatement strategies and the evidence to demonstrate compliance if questions are raised.

What Pollutants are Monitored?

Several categories of pollutant are commonly measured as part of a development-related air quality monitoring programme. The specific parameters included will depend on the nature of the site and the source emission of certain pollutants likely to be present.

Nitrogen Dioxide (NO2)

This is one of the most commonly monitored pollutants in an urban context.

It is produced primarily by road traffic and combustion processes, including those associated with construction plant and equipment. It is a key indicator of traffic-related air pollution and is closely regulated under national air quality objectives.

Particulate Matter

This is measured in two size fractions: PM10 (particles with a diameter of ten micrometres or less) and PM2.5 (particles with a diameter of 2.5 micrometres or less).

Fine particulate substances are a significant concern in the context of construction activity, where earthworks, demolition, material handling and vehicle movements on unpaved surfaces can generate substantial dust.

PM2.5 in particular is associated with adverse respiratory and cardiovascular health effects at relatively low concentrations.

Carbon Monoxide (CO)

CO is produced by incomplete combustion.

It is a concern where large concentrations of vehicles, generators or plant machinery are operating in confined or poorly ventilated areas.

Sulphur Dioxide (SO2)

This arises primarily from the combustion of fossil fuels and from certain industrial processes.

While less commonly the primary focus of development-related monitoring, it is included in many monitoring programmes, particularly for industrial or energy-related development proposals.

Ozone (O3)

O3 is a secondary pollutant formed in the atmosphere through chemical reactions involving other pollutants in the presence of sunlight.

It is monitored as part of broader air quality assessment programmes. 

Benzene

Benzene and other volatile organic compounds (VOCs) may be relevant where a development site includes industrial areas or commercial use, or where contaminated land has been identified.

Indoor air quality monitoring covers a different but related set of parameters, including carbon dioxide (CO2), VOCs and particulate matter within buildings.

It is particularly relevant to development projects involving the refurbishment or change of use of existing buildings, and to residential developments where future occupiers may be exposed to air pollutants from nearby roads or industrial activities.

Air Quality Monitoring Methods and Standards

Monitoring must be carried out in accordance with established standards to produce air quality data that is accepted by local planning authorities and their technical advisers.

The principal compliance monitoring network in the UK is the Automatic Urban and Rural Network (AURN), operated by DEFRA and the Environment Agency, which sets the methodological framework against which monitoring data is assessed. 

Standard measurement techniques are specified for each pollutant type. Nitrogen dioxide and nitric oxide are measured using chemiluminescence.

Sulphur dioxide is measured using UV fluorescence. Carbon monoxide uses infrared absorption. Ozone is measured using UV absorption. Particulate matter is measured using one of several approved methods including beta attenuation monitoring, tapered element oscillating microbalances and gravimetric analysis. 

Ambient Monitoring

These methods are underpinned by standards developed by the European Committee for Standardisation (CEN) in conjunction with the European Commission, which set out minimum performance requirements and data quality objectives in line with the Ambient Air Quality Directive (2008/50/EC).

UK compliance with these standards is maintained through DEFRA’s national monitoring networks, which comprise around 300 Environment Agency-managed sites in total across the UK, organised into automatic and non-automatic networks measuring different pollutants by different methods.

In practical terms, monitoring equipment deployed on a development site must be sited, calibrated and operated in a way that produces air quality data of sufficient quality to meet these standards. This requires specialist knowledge and experience: the involvement of a qualified air quality consultant is essential to ensure that the monitoring programme is designed and executed correctly.

Monitoring During Construction

Dust generated during construction is one of the most frequently raised air quality concerns associated with development projects. Earthworks, demolition, concrete cutting, material stockpiling and vehicle movements across unpaved surfaces can all produce significant quantities of airborne particulates, affecting neighbouring properties and sensitive environmental receptors.

The Institute of Air Quality Management (IAQM) publishes guidance on the assessment of dust from demolition and construction – currently version 2.2, published in January 2024 – which is widely used by local planning authorities and their consultees as the basis for assessing dust risk and specifying mitigation measures. A dust management plan, developed in line with this guidance, will typically be required as a planning condition for any development of meaningful scale.

Air quality monitoring during the construction phase provides the data analysis to demonstrate that dust controls are operating effectively and that agreed threshold levels are not being exceeded. Where monitoring indicates that dust or emission levels are approaching or exceeding agreed limits, mitigation measures can be adjusted in real time to prevent a breach.

Air Quality Monitoring Equipment

The equipment used in a monitoring programme will depend on the pollutants being measured and the duration and intensity of the monitoring required. Commonly used instruments and systems on air quality monitoring stations include:

• Continuous automatic analysers for gaseous pollutants including NO, NO2, SO2, CO and O3, using the measurement techniques referenced above.
• Particulate monitors for PM10 and PM2.5, including beta attenuation monitors, optical instruments and gravimetric systems.
• Passive diffusion tubes for nitrogen dioxide, widely used for longer-term monitoring at multiple locations due to their low cost and ease of deployment.
• Dust deposition gauges and real-time dust monitors for construction phase monitoring.
• Meteorological instruments including weather stations, wind speed and direction sensors, temperature and humidity loggers, which provide the contextual data needed to interpret air quality measurements correctly.
• Data loggers for continuous recording and remote data retrieval. 
• Mobile monitoring laboratories for intensive short-term measurement campaigns.

Organising Air Quality Monitoring

The starting point is to engage a qualified air quality consultant who can assess the scope of monitoring required for your project and provide reliable data.

They will design a monitoring programme that will produce data of the quality needed for planning purposes, protect human health and oversee the deployment, operation and analysis of monitoring equipment throughout the required period.

Consultants will be able to advise on abatement strategies such as pollution control measures to satisfy local government requirements.

Air quality consultants should hold relevant professional qualifications and ideally be members of the Institute of Air Quality Management (IAQM) or a similarly recognised professional body.

The monitoring programme should be agreed with the local planning authority or its technical adviser at the pre-application stage wherever possible, to ensure that the data collected will meet the requirements of the planning process.

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