Particle Concentrations and Numbers Network


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.

What is the purpose of the network?

The purpose of the Particle Concentrations and Numbers (PCN) Network is to monitor the compliance with objectives set out in the UK's Air Quality Standards Regulations (AQSR) 2010, including associated amendments 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 particle 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 of air (for example µg m-3). Particle mass concentrations are typically dominated by larger sized particles.

How is the network run?

The PCN Network is run by the National Physical Laboratory (NPL) in partnership with the Environment Research Group (ERG) at Imperial College London (ICL) on behalf of Defra and the Devolved Administrations. The data analysis and interpretation focuses on:

  • Analysis of PM components that feature in the AQSR 2010, specifically nitrate, sulfate, ammonium, elemental carbon, and organic carbon.
  • Analysis of particulate concentrations, in terms of the relationships between different size fractions, emission sources, episodes of high particulate pollution, and contribution of windblown suspended particles.
  • Seasonal variations and local meteorological factors related to changes in particle mass and number concentrations.
  • Diurnal variations in particle number concentrations and chemical composition.
  • Relationships between particle number concentrations and chemical composition from sites in the network, and information taken from other ratified data sets such as AURN data.
  • Comparative analysis between secondary particles, the PM2.5 fraction and particle sizes and numbers.
  • Statistical analyses to determine the relationships of PM components with indicators of other emission sources.

Research reports and annual reports from this network can be found in the Library section of this website.

Monitoring methods

The network comprises a range of analysers at several locations and draws on data from other networks (such as the AURN) to further understanding of the composition of PM in the UK.

Table 1: Particle numbers and concentrations monitoring network
SiteDigitel (PM2.5)SMPSCPCXRF
PM10 & PM2.5)
(PM2.5 or
Chilbolton X
X X    X

London Honor
Oak Park

London Marylebone Road X X X X X*
Auchencorth Moss  X        
  • Digitel aerosol sampler - Ultrapure quartz filters are sampled to allow for the analysis of PM2.5 Elemental Carbon and Organic Carbon (EC/OC).
  • SMPS - Scanning Mobility Particle Sizers measure particle size distributions.
  • CPC - Condensation Particle Counter measure particle number concentrations
  • XRF - X-ray fluorescence spectrometer to determine elemental concentrations (> 40 elements) in ambient aerosols. The instrument includes a switching inlet which alternates between PM2.5 and PM10 every hour.
  • ACSM – Aerosol Chemical Speciation Monitor uses Aerosol Mass Spectrometer technology to provide quantitative chemical composition measurements for organic aerosol, nitrate, sulphate and ammonium. The instrument uses a PM2.5 or PM1 inlet.

Please note: Black Carbon is measured by the UK Black Carbon Network.

View data for sites in this network

Data can be downloaded from the Data Archive section of this website.

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