Air quality

‘Air quality’ describes the cleanliness of the air we breathe, and ‘poor air quality’ means that the air is polluted with gases and particles which are harmful to our health.

Nitrogen dioxide (NO2 or NOx)

NO2 is an invisible gas produced when fossil fuels are burned, for example, petrol and diesel in vehicle engines, and gas in boilers and gas stoves. NO2 is sometimes expressed as ‘NOx’, which includes NO2 and nitrogen oxide (NO), another gas produced at the same time as NO2.

NO2 is a respiratory irritant and can cause inflammation of the airways. This can lead to coughing, wheezing, and shortness of breath. Exposure to NO2 can reduce lung development in babies and children, which can affect lung health throughout life.

Particulate matter 

Particulate matter (PM) refers to solid or liquid particles suspended in the air. PM is often written as ‘PM10’ or ‘PM2.5’; the number indicates the size of the particles in micrometres (a micrometre is one-thousandth of a millimetre). For comparison, human hair is about 50 micrometres in diameter. PM2.5 is referred to as ‘fine particulate matter’ because it is so small and can reach deep into the lungs and even the bloodstream.

The majority of PM is from human activities such as burning fossil fuels in vehicle engines, in kitchens and in open fireplaces and wood-burning stoves. Outdoor fires (such as garden bonfires) are also a source of PM. PM is also produced when building materials are crushed or broken on construction sites, and by friction between surfaces such as vehicle tyres on roads.

You can read more about what we are doing to improve air quality on the Improving air quality page. 

For further information about air quality and health, visit Public Health England’s Health matters: air pollution.