Publications

2022

Indoor Air Quality

Indoor environments are diverse in type and the behaviour of pollutants within them is determined by complex chemical and physical processes. The scope of this report focuses on air pollutants in residential indoor environments, people’s exposure in commuting and transport hubs, retail spaces and sports venues and locations with vulnerable populations. This report examines the evidence of this complex environment highlighting evidence challenges and opportunities for improvements associated with i) emissions and sources, ii) pollutant distribution, trends, and effects iii) measurement iv) interventions and actions to improve indoor air quality.

2021

Ozone in the UK – Recent Trends and Future Projections

Ozone at ground level, in contrast to the ozone layer, is a pollutant that is harmful to human health, damaging to plants, leading to agricultural losses and is damaging to buildings. Ozone a few miles above ground level is also a greenhouse gas. As a secondary pollutant, ozone is created in the atmosphere through reactions involving its pre-cursor pollutants: volatile organic compounds (VOC) and nitrogen oxides (NOx), in the presence of sunlight. This report prepared by the Air Quality Expert Group (AQEG) for Defra and the Devolved Administrations updates AQEG’s 2009 report on ozone in the UK by reviewing measured concentrations of ozone across the UK and predicting future concentrations.

Exhaust Emissions from Road Transport

Pollutants in exhaust emissions cause harm to health, the environment and contribute to climate change. Transport sources form a majority of NOx emissions and a significant part of PM emissions. This report prepared by the Air Quality Expert Group (AQEG) for Defra and the Devolved Administrations, covers exhaust emission standards (EURO Standards), measurements techniques (ambient, laboratory and in real-world driving conditions) and the validation of emissions and measurements. The report also highlights interventions for reducing exhaust emissions.

Modelling of future PM2.5 concentrations

On 19 November 2020 AQEG launched a call for evidence on the modelling of future PM2.5 concentrations in order to inform their advice to Defra on the development of AQ targets required by the Environment Bill. This call sought evidence from the results of modelling as to the concentration and future composition in England, the main drivers of future changes, key modelling uncertainties and information relating to on how population exposure might change.

From the responses received AQEG selected a number to present to them at an online workshop. AQEG produced a summary of what was learned from the call for evidence and made a number of recommendations to Defra. This information is informing the modelling approach being taken and provides context to the work, for example highlighting the technical complexities and uncertainties involved in air quality modelling.

Defra – AQEG Initial engagement on AQ target setting

Early in the process for developing AQ targets required by the Environment Bill, Defra asked AQEG for their initial views on a number of technical aspects relating to the proposed targets, and how they wished to be engaged in the target setting process. Following an online meeting with Defra, AQEG provided a summary note providing some preliminary advice.

Please note that this advice was provided at an early stage of the development process and some points may have been superseded or greater detail/qualification added at a later date. This initial advice helped to inform Defra’s initial decision-making on areas such as metrics, measuring progress and modelling.

2020

Estimation of changes in air pollution emissions, concentrations and exposure during the COVID-19 outbreak in the UK

This report synthesises submissions to an informal and rapid call for evidence by the Air Quality Expert Group on COVID-19 and air quality. The reported evidence shows that there was a drop in the emissions and concentrations of some pollutants. Observed concentrations varied by pollutant, with NO2 levels showing a consistent drop while PM2.5 exhibited a more variable pattern. Analysis based on the pollutant level also suggested a possible associated drop in individual exposure to pollutants. A contribution to the report by the Committee on the Medical Effects of Air Pollutants suggested the possibility that past exposure to air pollution was likely to impact on Covid-19 but noted the need for further studies and evidence on this.

Impacts of Net Zero pathways on future air quality in the UK

This report evaluates the possible air quality implications of a wide range actions to reduce greenhouse gas emissions from emission sectors in the UK as part of the Committee on Climate Change’s Net Zero scenario. Encouragingly, the report finds, that for virtually all of the changes proposed on the CCC Net Zero pathway, positive, improved and better air quality outcomes can be envisaged. However, the report highlights several areas where the options adopted need to be carefully assessed from an air quality perspective to ensure the pathway to that end goal is as beneficial as possible.

Non-methane Volatile Organic Compounds in the UK

Non-Methane Volatile Organic Compounds (NMVOCs) are a broad class of organic compounds that are regulated because, in a small number of cases, they are directly harmful to health. More notably, NMVOCs are precursors of ozone and particulate matter (PM) formation, secondary pollutants that are directly harmful to human health and the environment. This report considers trends in NMVOC emissions, overviews their source sectors in the UK and evaluates the effectiveness of the current NMVOC monitoring network, the UK Hydrocarbon Network.

Assessing the Effectiveness of Interventions on Air Quality

This report reviews methods that have been used to evaluate the effectiveness of interventions intended to reduce air pollution and associated health effects. The intention is to explain the different approaches that have been used and to highlight the requirements for undertaking a robust evaluation. The report does not provide information on the effectiveness of different types of intervention that might be implemented.  Nonetheless, the overview of the approaches used, and their strengths and limitations, should prove helpful to organisations considering the implementation of interventions and wishing to evaluate their effectiveness.

2019

Non-Exhaust Emissions from Road Traffic

Non-exhaust emissions from road traffic are particles that arise from the wear of brakes, tyres and the road surface and from the resuspension of road dust. These emissions arise from all vehicle types and are independent of vehicle mode of power. This report, prepared by the Air Quality Expert Group (AQEG) for Defra and the Devolved Administrations, looks to summarise current evidence for the non-exhaust emissions of particles from road transport at the point of on-road usage.

2018

Air Pollution from Agriculture

88% of the UK's harmful ammonia emissions came from the agricultural sector in 2016, so it is important to understand the mechanisms for emission and potential options for control. This report, prepared by the Air Quality Expert Group (AQEG) for Defra and the Devolved Administrations looks at the evidence and policy aspects of air pollutants from agriculture.

Impacts of Vegetation on Urban Air Pollution

Existing urban vegetation and potential planting schemes can influence atmospheric composition through emission of trace gases and by dispersion and deposition of air pollutants. As a consequence, vegetation may affect the concentrations of pollutants to which people in urban areas are exposed. This report, prepared by the Air Quality Expert Group (AQEG) for Defra and the Devolved Administrations looks at the available evidence on the impacts of vegetation on urban air quality. In summary AQEG conclude that vegetation and trees in particular are regarded as beneficial for air quality, but they are not a solution to the air quality problems at a city scale.

Ultrafine Particles (UFP) in the UK

Ultrafine particulate matter can dominate the total number of particles in polluted air and can be harmful for human health. This report, prepared by the Air Quality Expert Group (AQEG) for Defra and the Devolved Administrations, looks at the available evidence on the impact of the ultrafine particle (UFP) component on UK ambient air quality.

Potential Air Quality Impacts of Shale Gas Extraction in the UK

Shale exploration is a nascent area. Most existing studies on the air quality implications are US-based, having limited applicability to the UK context. This report, prepared by the Air Quality Expert Group (AQEG) for Defra and the Devolved Administrations, looks at the available evidence in 2015 on the potential air quality impacts of shale gas extraction in the UK.

AQEG Advice - on the concept of ‘zero emission vehicles’

With a drive to reduce the emissions from road transport, attention has turned to vehicles that produce lower emissions than those powered by conventional internal combustion engines. This has given rise to the term “zero emission vehicle” which is, for example used to describe battery electric and hydrogen powered vehicles. AQEG explain that this description is intended to highlight that the vehicle has no exhaust emissions, but it could also be inferred that there are no emissions associated with the running of the vehicle at all; they recommend the use of the term "zero exhaust emission vehicle" instead.

AQEG Advice on the use of 'low-cost' pollution sensors

Low-cost sensors are highly attractive for many different reasons – they potentially allow for far greater density of measurements to be made, let individuals measure pollution in their local environment, they may be carried on a person to estimate exposure, or be integrated into networks into local air pollution management systems.

Many different low-cost sensors are being commercialized and the technology and marketplace is evolving very rapidly. For this reason it is difficult for Defra and the Air Quality Expert Group to use its usual format of detailed review reports to provide updates or advice to interested parties on the state of the art. There is a substantial risk that such studies may well be out of date by the time of publication.

Instead Defra and AQEG will use this part of the UK-Air website to provide regular updates on the science and application of air pollution sensors, their uncertainties and recommendations and advice on where they may, or may not, be appropriate to use. Links to the latest review articles on this subject will also be provided.

2017

Impacts of Shipping on UK Air Quality

Shipping makes significant contributions to emissions of primary air pollutants and to the production of secondary pollutants. The relative contribution of emissions from shipping is greater in the vicinity of the UK than across other areas of Europe because of the UK’s location adjacent to major shipping lanes and its major port activities. This report, prepared by the Air Quality Expert Group (AQEG) for Defra and the Devolved Administrations looks at the available evidence on the impacts of shipping on UK air quality.

The Potential Air Quality Impacts from Biomass Burning

National energy statistics show an increasing trend in the combustion of wood in the UK and both measurements and inventories suggest that particulate matter from biomass burning is on the increase. A range of incentives that encourage the use of biomass burning for power and heat generation could have adverse air quality impacts. This report, prepared by the Air Quality Expert Group (AQEG) for Defra and the Devolved Administrations looks at the available evidence on the potential air quality impacts from biomass burning.

2016

Paints and Surfaces for the Removal of Nitrogen Oxides

There is increased interest in the use of outdoor photocatalytic surfaces (surfaces that act as a catalyst when exposed to light) as a means of reducing concentrations of various pollutants; principally nitrogen oxides (NOx which includes nitrogen monoxide, NO and nitrogen dioxide, NO2), and particularly NO2.
 
The report on Paints and Surfaces for the Removal of Nitrogen Oxides, prepared by the Air Quality Expert Group (AQEG) for Defra and the Devolved Administrations looks at the available evidence on the efficacy of photocatalytic paints and surfaces and their impact on ambient concentrations of nitrogen oxides.

2015

Evidential Value of Defra Air Quality Compliance Monitoring

Defra's air quality monitoring networks support compliance reporting against European ambient air quality directives. For more information see http://uk-air.defra.gov.uk/networks/

The Evidential value of Defra air quality compliance monitoring report, prepared by the Air Quality Expert Group (AQEG) for Defra and the Devolved Administrations looks at the range of activities that Defra's air quality monitoring networks support beyond their core, mandatory reporting function.

Mitigation of UK PM2.5 Concentrations

Particulate matter (PM) is the term used to describe condensed phase (solid or liquid) particles suspended in the atmosphere. Their potential for causing health problems is directly linked to the size of the particles. A growing body of research has pointed towards the smaller particles, in particular PM less than 2.5 µm in diameter (PM2.5), as a metric that is more closely associated with adverse health effects than other metrics such as PM10.

The Mitigation of UK PM2.5 concentrations report, prepared by the Air Quality Expert Group (AQEG) for Defra and the Devolved Administrations addresses two issues: first, the contribution to PM2.5 (particulate matter with a diameter less than 2.5 µm) concentrations in the UK which arises from sources within the UK and which therefore sets a limit on the extent to which UK source abatement measures can mitigate UK PM2.5 concentrations; and second, the related issue of the role of ammonia emission reductions in mitigating PM2.5 concentrations compared with reductions in other sources/components of PM2.5, in particular primary combustion sources of PM2.5.

Linking Emission Inventories and Ambient Measurements

An emissions inventory is a database of all quantified releases of air pollutants by source for a specific location and during a given time period. It is important to verify emission inventories as a way of checking whether trends in ambient concentrations match those expected in emission inventories and, if they do not, to identify a potential cause and take any necessary action.

The Linking emission inventories and ambient measurements report, prepared by the Air Quality Expert Group (AQEG) for Defra and the Devolved Administrations considers the linkage between emission inventories and ambient measurements and aims to review information that could help establish a stronger link between them.

Fine Particulate Matter (PM2.5) in the UK

Particulate matter (PM) is the term used to describe condensed phase (solid or liquid) particles suspended in the atmosphere. Their potential for causing health problems is directly linked to the size of the particles. A growing body of research has pointed towards the smaller particles, in particular PM less than 2.5 µm in diameter (PM2.5), as a metric that is more closely associated with adverse health effects than other metrics such as PM10.

The PM2.5 in the UK report, prepared by the Air Quality Expert Group (AQEG) for Defra and the Devolved Administrations gives an overview of the evidence base for PM2.5 in the UK. The report challenges the robustness of the evidence for making future policy decisions in respect of PM2.5 in the UK context. There is an analysis of the evidence concerning key relevant aspects including PM2.5 measurement and the composition and current concentrations of PM2.5 across the UK, as well as source emissions and receptor modelling for PM2.5. Finally, AQEG evaluates the methods for modelling PM2.5 and what can be said about future concentrations. The report concludes with an assessment of the key uncertainties and gaps in the evidence base that require action.

Understanding PM10 in Port Talbot

AQEG was asked by Defra and the Welsh Assembly Government to provide an independent expert opinion on:

"What methodologies or approaches are required to advance the evidence base in order to assess the impact of the different current particle sources within the Port Talbot area on the resultant particulate matter (PM) levels in the local area?"

AQEG reviewed a range of evidence, including published reports and material gathered at a public evidence session held at Port Talbot. In the advice note AQEG make a series of recommendations intended to provide guidance on the future evidence gathering in Port Talbot to better understand the sources of PM10.

The Welsh Government has respond to AQEG on the recommendations made in the report

Road Transport Biofuels: Impact for UK Air Quality

This advice note looks at recent trends in biofuel consumption in the UK and summarises the effects of biofuels on vehicle emissions and air quality based on current evidence. The advice note addresses only the direct effects of consumption of biofuels on air quality in the UK resulting from end of tailpipe emissions.

AQEG recognise that tailpipe emissions are only one of many aspects which need to be considered in the full context of biofuel production and use and is not meant to diminish the importance of wider sustainability issues, both in the UK and globally.

AQEG conclude that consumption of biofuels as low strength blends up to 15% has little effect on air quality, but further research on the effects of high strength blends on emissions is required if their consumption were to be encouraged.

Older publications

For copies of old reports and publications published by the Air Quality Expert Group and minutes of AQEG meetings, please contact aq.secretariat@defra.gov.uk.