Air Pollution Companion: Knowledge hub - Deepen your knowledge

You can also start with the basics on air pollution.

If you have a topic you'd like us to delve deeper into, send us an email at cleanair@rcpch.ac.uk.

How is air pollution measured? A deep dive into monitoring and data

Types of monitor

Air pollution is measured using different devices, which vary in cost, accuracy and scale. These devices are classified as either passive or active:  

• Passive monitors collect air samples over time for later analysis in a lab. They are simple to use but do not provide real-time results.  
• Active monitors analyse air continuously using automated or semi-automated systems, providing real-time or near real-time data.

Sensors vary from portable, personal monitors to small static sensors and large-scale monitoring stations. Remote monitoring via drones and satellites can map pollution data on a much broader scale. And, remote sensing satellite instruments allow assessment of global exposures by observing aerosols in a column of air between the upper atmosphere and the earth's surface.

Air pollution monitoring uses ‘networks’ to examine exposure. Networks are comprised of a variety of sensor types, which together create a picture of both live and historical air pollution data. Within these networks, reference grade monitors are used to calibrate lower cost sensors and corroborate remote sensing satellite instruments; databases can weigh data differently dependent upon the source and reliability.

Real-world research has shown how portable monitors are used in studies to assess personal exposure to air pollution. For example:

• The SAMHE project provided over 1,300 schools across the UK with high-spec air quality monitors to track indoor pollution, enabling students and teachers to explore and improve classroom air quality using real-world data."
• Professor Jonathan Grigg’s work at the Royal London Hospital’s air pollution clinic uses portable monitors to assess children’s exposure and personalise asthma treatment.

Types of data

Network data can provide live, time-specific and historical levels of major pollutants. It can then be combined with meteorological information to provide further detail in both forecasting and impact assessment, whilst machine learning and AI tools are increasingly assisting with application and analysis.

Data modelling describes the visual representation of data which makes it easier to interpret. This is a useful tool for both clinicians and patients when understanding and talking about the effects of air pollution on health.  

For instance, tools like the DEFRA Daily Air Quality Index (DAQI) are really useful in providing accessible insights into air quality levels and their health implication. Similarly, the UN Environment Programme’s (UNEP) IQ Air platform offers global air quality data, helping individuals understand and mitigate exposure risks in real time

The UNEP IQ Air platform provides an Air Quality Index (AQI) on a scale from 0 to 500, whilst the Daily Air Quality Index (DAQI) from DEFRA, scores from 1 to 10. These scores are then divided into four bands, from 'low' to 'very high' the index translates to recommended actions to reduce the effects of pollution exposure.

Furthermore, interfaces exist which show how air pollution data corresponds with live traffic conditions, movement (ie walking, exercising, commuting) and weather changes. This allows personalisation of interpretation and actions/advice, which is particularly valuable with a healthcare lens.

Who is the most vulnerable? A deep dive into health inequalities

Although air pollution affects everyone, structural inequalities mean that some groups of children are more vulnerable to its health impacts. Despite contributing less to air pollution, low-income individuals, particularly from racial minority backgrounds, are exposed to higher pollution levels and suffer greater health impacts.1 This combination of lower emissions and greater vulnerability results in an unfair proportion of the health burden, raising concerns about environmental justice.

These disparities make addressing air pollution a complex challenge that demands a multifaceted response, as it is not only a public health issue but also one of equity.

Deprivation

Children in deprived households are often exposed to higher levels of outdoor air pollution. A 2015 study2 found that the most deprived 20% of neighbourhoods in England had significantly higher levels of air pollution compared to the least deprived, even after adjusting for other variables. 

Recent research3 also highlights disparities in indoor air pollution, with deprived households experiencing higher levels of particulate matter (PM), nitrogen dioxide (NO2), and volatile organic compounds (VOCs). These pollutants can lead to serious health issues in children, read more about the health impacts in our air pollution position statement.

Some factors contributing to this increased exposure include:

• Proximity to pollution sources: Many low-income areas are located near busy roads, factories, and other pollution sources.
• Inadequate housing: Poorly built homes often fail to effectively limit the infiltration of outdoor pollutants.
• Ventilation issues: Many low-income homes lack proper ventilation, which worsens indoor air quality. While improving energy efficiency through better insulation can reduce outdoor pollutants, it may inadvertently increase indoor pollution due to reduced airflow.
• Overcrowding: More occupants in a home means more dust and particulate matter in the air.
• Poor insulation: Fuel poverty leaves many deprived homes with limited resources to address issues like and damp and mould increasing their vulnerability to the health effects of air pollution. 

The tragic case of Awaab Ishak, a two-year-old from Rochdale, highlights the severe impact of poor housing conditions on health. Read more about Awaab's story in our air pollution position statement.

A diagram in UNICEF’s Breathless Beginnings Report illustrates how air pollution harms children's health at every life stage, worsening existing inequalities.

Race and ethnicity

Air pollution exposure is closely tied to both race and ethnicity. Ethnically diverse neighbourhoods - those with more than 20% of the population identifying as non-white - tend to have higher pollution levels.2

A 2024 study4 revealed significant disparities in air pollution exposure, highlighting the following key findings:

• Minoritised ethnic groups experience higher emissions regardless of deprivation.
• Minoritised white ethnic groups experience higher emissions than the majority white population.
• All major sources, including road transport, domestic heating, and industry, contribute to emissions disparities.
• The consistency of emissions disparities across various ethnic groups suggests a pattern of environmental injustice.

London case study

The most deprived communities of London are still more likely to be found in the highest pollutant concentration areas. The areas in London with the lowest NO2 and PM2.5 concentrations have a disproportionately white population. And diaspora communities are more likely to live in an area with higher pollution concentrations than the London average.5

In the UK, Black women face significant maternal health disparities, with air pollution playing a critical role6 :

• Black women are 3.7 times more likely to die during pregnancy than white women.
• Black women are twice as likely to experience stillbirth compared to white women.

Black Londoners are disproportionately exposed to illegal levels of air pollution, which significantly increases the risks of stillbirth, pre-term birth, and miscarriage.

The Black Child Clean Air report, by Global Black Maternal Health, highlights the urgent need for intersectional approaches in environmental advocacy and policymaking. The report reveals how air pollution is intricately linked to maternal health outcomes and calls on policymakers to act to protect Black women and children from harmful exposure. 

Why are minoritised communities affected?

• Proximity to pollution sources: Many minoritised communities live near major pollution sources, such as factories, power stations, refineries and waste incinerators. This exposes them to higher levels of harmful pollutants: See the case study of DRAX power station on page 12 of A just energy transition for the good of health from UK Health Alliance on Climate Change.
• Economic barriers: Minoritised communities tend to have lower incomes, which limits their housing options. Affordable housing is often located in more polluted areas, as cleaner, greener neighbourhoods are more expensive. 
• Heath vulnerability: Minoritised communities often experience higher levels of pre-existing medical conditions such as asthma, cardiovascular disease or cystic fibrosis, that increase their vulnerability to the adverse health impacts of air pollution.
• Urban density and the urban heat island effect: Many minoritised communities also live in areas that are more susceptible to the "urban heat island" effect, where lack of green spaces and heat-absorbing infrastructure cause temperatures to rise, which can exacerbate air quality issues. Read more about the link between climate change and air pollution on our 'Start with the basics' page.

It’s important to note that while higher levels of deprivation and living in urban areas contribute to higher emissions, they don’t fully explain why minoritised ethnic groups face greater exposure. Even when these factors are accounted for, disparities still exist. The 2024 study4 suggests that deeper, long-term issues such as differences in local economies, industries, transport systems, and migration patterns also play a role in the unequal exposure to pollution. For instance, road transport accounts for about 48% of these disparities, and domestic heating is a major contributor to PM2.5-related pollution.

To reduce these inequalities, tackling emissions from sources beyond road transport will be key moving forward.

Don't forget, we have a list of resources, including a link to a helpful glossary.

• 1 www.theguardian.com/environment/2023/jul/28/air-breathe-uk-depends-race-income
• 2 a b Fecht, D., Fischer, P., Fortunato, L., Hoek, G., de Hoogh, K., Marra, M., Kruize, H., Vienneau, D., Beelen, R., & Hansell, A. (2015). Associations between air pollution and socioeconomic characteristics, ethnicity and age profile of neighbourhoods in England and the Netherlands. Environmental Pollution, 198, 201-210. https://doi.org/10.1016/j.envpol.2014.12.014 
• 3Ferguson, L., Taylor, J., Davies, M., Shrubsole, C., Symonds, P., & Dimitroulopoulou, S. (2020). Exposure to indoor air pollution across socio-economic groups in high-income countries: A scoping review of the literature and a modelling methodology. Environment International, 143, 105748. doi.org/10.1016/j.envint.2020.105748
• 4 a b Gray, N.R., Lewis, A.C., & Moller, S.J. (2024). Evaluating disparities in air pollution as a function of ethnicity, deprivation and sectoral emissions in England. Environment International, 194, 109146. https://doi.org/10.1016/j.envint.2024.10914
• 5Greater London Authority, 2023. Air Pollution and Inequalities in London - update 2023. Greater London Authority. Available at: www.london.gov.uk/programmes-strategies/environment-and-climate-change/environment-and-climate-change-publications/air-pollution-and-inequalities-london-update-2023
• 6Global Black Maternal Health. (2023). Black Child Clean Air Report. Global Black Maternal Health. Available at: urbanhealth.org.uk/partnerships/current-partnerships/understanding-black-mothers-views-on-air-pollution