When is an Air Quality Assessment Required?

The air we breathe affects our everyday lives and has a significant impact on our health.

Air quality assessments for proposed Federal actions are required for compliance with the National Environmental Policy Act (NEPA), the Clean Air Act, and other environment-related regulations and directives.

Proposals that impact upon air quality, or result in new exposure to potential pollutants, must be supported by an air quality assessment. This may be a basic (or screening) assessment or a complex detailed dispersion modelling assessment.

There are various types of air quality assessment required depending on the size, location and future use of the development.

The most effective way to find innovative solutions in minimising the air quality impact of a development is for air quality to form part of the feasibility assessment.

Understanding the Clean Air Act

The Clean Air Act was implemented to remedy the damaging effects that bad air quality can have on human health and the environment.

Although it is a federal act applied nationally, much of the work and planning is done at the state and local level to tailor air quality requirements to local needs.

The Environmental Protection Agency (EPA) sets National Ambient Air Quality Standards (NAAQS). These are limits on certain “criteria” air pollutants, including limits on how much of these pollutants can be in the air anywhere in the United States.

Geographic areas that are in compliance with standards are called “attainment areas,” while areas that do not meet standards are called “nonattainment” areas.

In addition to the EPA, the Clean Air Act is administered by state, tribal, and local agencies, which are responsible for developing local solutions to air quality problems.

Federal projects must conform to Clean Air Act requirements if they may constitute a significant new source of air pollution.

If your project’s county or air quality management district is in attainment status for all criteria pollutants, the project is in compliance with the Clean Air Act.

If the project’s estimated emissions levels are below de minimis levels for all nonattainment or maintenance pollutants, the project is in compliance with the Clean Air Act and no further action is required.

Air Quality Assessment in the UK

In the UK, all applications for major developments, and any with car parking spaces above a certain threshold, typically require an Air Quality Assessment (AQA), which will address the air quality impacts of both the construction and operational phases of the development on human health and ecological receptors.

The exact requirements and thresholds vary by planning authority and may be detailed in planning validation requirements, supplementary planning documents, policy documents, or simply by the Environmental Health Officer during consultation.

Typically, impacts requiring assessment arise from dust generated during demolition and / or construction works, emissions from plant, or from the traffic generated by the development. Where impacts are identified, they may require proposal of mitigation measures, sometimes supported by damage cost calculations.

How to Conduct an Air Quality Assessment

What Information Should Be Included in an Air Quality Assessment?

The information that should be included in an air quality assessment for a planning application will differ depending upon the proposed development and the local requirements. In general air quality assessments can be divided into basic assessments and detailed assessments.

Basic Air Quality Assessment

This may include:

• A review of baseline air quality around the development site and affected road links, typically this can be achieved using existing published air quality monitoring and / or modelling data from the local authority or Defra, in the UK.
• An assessment of the impact on air quality during the construction phase. There is a standard methodology for assessment of construction dust impacts from the Institute for Air Quality Management, or variation of its guidance, adopted by most authorities. This takes a risk-based approach to defining appropriate mitigation for controlling dust and pollution emissions associated with plant and vehicles.
• Screening of predicted traffic generation of the development, against threshold levels, to inform the requirement, if any, for detailed assessment.
• Identification of receptors (potential exposure locations) which may be subject to a worsening of air quality as a result of the development, for example, due to traffic increases, or consideration of the potential exposure of new receptors (e.g. if building in an Air Quality Management Area).
• Consideration of the significance of the air quality effects, and whether they are a material constraint to development.
• A description of mitigation measures to be incorporated into the design, either to mitigate off-site impacts (e.g. promotion of sustainable travel solutions), or to mitigate exposure of occupants of the new development e.g. measures to reduce exposure such as green infrastructure, orientation or elevation of residential areas, building ventilation and (NOx / particulate) filtration requirement (the latter may require support using detailed methodology, see below).

Detailed Air Quality Assessment

Detailed air quality assessment would typically incorporate most of the elements of the basic assessment but may additionally include:

• Air quality monitoring - deploying automated or passive (diffusion tube) type monitoring at potential exposure locations of interest.
• Air quality dispersion modelling of either traffic emissions or combustion plant such as boilers, biomass boilers, combined heat and power plants (CHPs), or other industrial processes.

For a traffic emissions dispersion modelling assessment this would require:

• A model validation / verification assessment, where model predictions, based on recent measured traffic flow data are compared to air quality monitoring data for the same period to assess the accuracy of the model.
• The prediction of future air quality without the development in place (the future baseline or ‘without development’ scenario) at the receptor points of concern.
• The prediction of future air quality with the development in place (the ‘with development’ scenario) with predicted future road transport emissions.

This may lead to an additional scenario with the prediction of future air quality with the development with identified mitigation measures in place.

Air Quality Mitigation Requirements

Developments may need to incorporate specific air quality mitigation, either to reduce the predicted impacts to acceptable levels or as a result of planning policy (e.g. established policy requirements include Low NOx Boilers and numbers of Electric Vehicle charging points).

Typical mechanisms to facilitate mitigation include:

• Air Quality Neutral / Air Quality Positive assessments in London - use of emissions benchmarks based upon building energy usage and car trips to determine impact compensation or abatement compensation.
• Damage Cost Calculations - impact costs per tonne of emission by pollutant, based on theoretical societal costs to inform the scale of the required investment in air quality mitigation or off-setting measures.
• Dispersion modelling assessments - these allow detailed consideration of design strategies, whether this be locations of residential occupancy, ventilations strategies (e.g. Indoor air quality (also called "indoor environmental quality") describes how inside air can affect a person's health, comfort, and ability to work. It can include temperature, humidity, lack of outside air (poor ventilation), mold from water damage, or exposure to other chemicals.