Air quality, pollution and aviation noise

Air pollution and why it's important

Air pollution

The term ‘air quality’ refers to the cleanliness of the air we breathe. Major pollutants that contribute to poor air quality in urban areas are nitrogen dioxide (NO2) and particulate matter (PM). 

NO2 is a poisonous, invisible gas and is one of a family of related gases called nitrogen oxides, or NOx. NO2 forms when fossil fuel is burned, for example in petrol or diesel vehicle engines or gas in boilers. NO2 is a respiratory irritant and can have a variety of harmful effects on the lungs, including inflammation, worsened coughing and wheezing, and increased asthma attacks. 

Particulate matter (PM) is tiny particles, or pieces, of solids or liquids that are in the air. Human activities are a significant source of PM pollution, such as burning of fossil fuels or construction activities. PM10 and PM2.5 refers to the size of the particles in micrometres (one-thousandth of a millimetre). Both PM10 and PM2.5 can be harmful to your health, with PM2.5 the more dangerous of the two due to the particles being so small that they can reach deep into the lungs and bloodstream. Long-term exposure to PM can increase the risk of heart and lung disease, while short-term exposure can worsen existing health conditions. 

Health impacts of air pollution

Exposure to polluted air can seriously impact your health regardless of your age or existing health status. Both short-term and long-term exposure to air pollution can cause and contribute to a variety of chronic illnesses such as asthma, heart disease, and cancer. Recent studies even suggest air pollution can contribute to cognitive decline.

It is estimated that air pollution exposure causes between 28,000 and 36,000 early deaths each year in the UK, and about 9,400 in London. While everyone is at risk from exposure to poor air quality, air pollution disproportionately affects more vulnerable communities, such as children, older people, pregnant women, and people with pre-existing health issues. 

In this section, you will find out more about air quality in your local area, how it is measured, and the steps the Council is taking to improve air quality in the Borough and protect the health of residents.

For more information about air quality and its impact on health, visit Public Health England’s health matters: air pollution page.

Two core reports into the effects of air pollution in London and Hounslow include a 2020 study by Imperial College London (ICL), and a 2015 study by King’s College London (KCL).

  • The Kings College London study estimated the number of years of life lost, which is translatable to attributable deaths, due to of concentrations of particulate matter 2.5 µg m-3 (PM2.5) and Nitrogen dioxide (NO2) in London in 2010. KCL estimated there were 102 attributable deaths in Hounslow in 2010 as a result of PM2.5. It estimates there were 3537 attributable deaths in Greater London in total.
  • The Imperial College London study was commissioned by the GLA to assess the impact of the Mayor of London’s air quality policies and existing air pollution levels in the capital on public health. This was developed using 2019 and future levels of air pollution up to 2050 (projected from 2013). The Imperial College London study estimated that between 114-128 deaths could be attributed to concentrations of NO2 and PM10 in the borough in 2019.

Legal Limits of Air Pollution

The UK government has set national legal objectives for the concentration of air pollutants across the country. The World Health Organisation (WHO) has also set guideline recommendations for air pollutants. These are set out below.

Borough-wide, Hounslow is meeting the national objectives for annual mean levels of the gas Nitrogen Dioxide (NO2) as well Particulate Matter (PM10 and PM2.5). The UK’s national objectives are significantly higher than World Health Organisation recommended guideline values. For this reason, in the 2018 in the London Environment Strategy, the Mayor of London committed to meeting the 2005 WHO recommended guideline values across London by 2030. Additionally in September 2021, prior to the World Health Organisation’s revision of its recommended guideline limits, Hounslow Council committed to working towards the 2005 WHO guidelines for Particulate Matter, which 2022 data shows is being exceeded slightly (see table 1 below).

In 2021 the World Health Organisation (WHO) revised its guidelines to much more stringent levels and Hounslow is exceeding the updated WHO guidelines. A key area of focus is to help the Mayor meet the 2030 target and work towards the new WHO guidelines.

Table 1 – Summary of legal limit values for air pollutants


Hounslow 2022 Annual Mean

UK National Legal Objective

WHO 2021 Guideline

WHO 2005 Guideline

Nitrogen Dioxide (NO2)

27.9 µg/m3

40 µg/m3

10 µg/m3

40 µg/m3

Particulate Matter (PM10)

21.4 µg/m3

40 µg/m3

15 µg/m3

20 µg/m3

Particulate Matter (PM2.5)

10.8 µg/m3

20 µg/m3

5 µg/m3

10 µg/m3

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