Image: Marylebone Road air quality monitoring station

Particulate matter (PM) in the atmosphere generally comprises solids and liquids, with particle sizes that range from a few nanometres (nm) in diameter to about 100 micrometres (µm). The chemical composition of PM is varied and the constituents of PM at any location will depend on many factors such as emission sources and meteorological conditions. 

The purpose of this network is to monitor the UK's compliance with objectives set out in the EU Ambient Air Quality Directive and to improve the understanding airborne particulate matter through scientific research. 

Exposure to airborne PM is associated with a range of adverse effects on human health including effects on the respiratory and cardiovascular systems, leading to hospital admissions and mortality. There is increasing evidence that fine (PM2.5) and ultrafine particulate matter (<100nm) plays a more significant role than previously thought, although as yet the precise toxicological mechanisms are not clearly understood. There is also evidence to suggest that particle number concentrations and chemical composition are of greater significance than mass concentrations in the determination of certain health effects. Particle number concentration is the total number of particles per unit volume of air (for example cm-3), whereas particle mass concentration is the total mass of particles per unit volume (for example µg m-3). Mass concentrations are typically dominated by larger particles. 

The Particle Numbers and Concentrations Network is run by the National Physical Laboratory (NPL) in partnership with Imperial College on behalf of Defra and the Devolved Administrations.  

PI: Dr Dave Green