What is particulate matter?

Anything in the air that is not gas is particulate matter. The term particulate matter covers particles of many sizes, types, and sources. Some of these particles are natural such as sea spray and pollen, but most are derived from human activities and from a variety of sources including agricultural chemicals, brake and tyre wear from vehicles, and the combustion of fuels and other materials.

These particles are measured in several ways and are usually grouped and labelled as PM10 (‘coarse’ particulate matter) to refer to particles smaller than 10 micrometres in diameter and PM2.5 (‘fine’ particulate matter) to refer to particles smaller than 2.5 micrometres in diameter. Any measurement of PM10 also includes all PM2.5. Grouping particles by size makes it possible to measure the concentrations of particles in the air in a meaningful way.

Emissions of particulate matter are the amounts of particulate matter produced and released into the air by a specific activity or attributed to a specific source (or sources) of this pollution. The concentration of particulate matter is the mass of particulate matter measured in a certain volume of air in a specific location and at a specific point in time (or a defined time period). It is usually given in units of micrograms (one-thousandth of one gram) per cubic metre of air (µg/m3)

There can be a large difference between these as some particles will stay airborne for longer, and the weather has a huge impact on concentrations, often spreading particles a long way from where they were produced or bringing particles from far away into our homes.

When we breathe in airborne particles the nasal lining and hairs can trap more of the larger particles and stop them travelling into our lungs. The smaller a particle is the more likely it is to make it to the lungs and into the circulatory system and, from there, travel to any organ.

The Environmental Targets Regulations 2023 introduced updated pollution limits for PM2.5 air pollution to be achieved throughout the UK by 2040 at the latest:

  • An annual average of 10 µg/m3 for PM2.5 not to be exceeded at any monitoring station.
  • A reduction in population exposure to PM2.5 of at least 35% compared to a baseline year of 2018.

To meet the new targets, we will need to reduce emissions from all sources of PM2.5 that we can control.  An estimate provided by Defra shows that about 15% of the PM2.5 in our air is natural and about half of the rest is generated in the UK, with the rest coming from other countries, shipping, or unknown sources.

The importance of communities, towns, counties, and countries working together to reduce particulate air pollution is clear.  The work that we put in locally to reduce the emissions of particulate air pollution can have a very wide impact.

Member London Boroughs