Particle Numbers and Concentrations 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 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.

How is the network run?

The Particle Numbers and Concentrations Network is run by NPL in partnership with Imperial College on behalf of Defra and the Devolved Administrations. The data analysis and interpretation focuses on:

  • Analysis of PM components that feature in the EU Ambient Air Quality Directive Annex IV, specifically anions, cations, elemental carbon and organic carbon.
  • Analysis of particulate mass concentrations, PM2.5, 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 variation in mass concentration and particle number concentrations.
  • Relationships between particle mass and number 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
SitePartisol (PM2.5)Leckel (PM2.5) SMPSCPCURG-9000B
X X X    

London Honor
Oak Park

X   X X X X
London Marylebone Rd X   X X X
Auchencorth Moss   X        

CPC - Condensation Particle Counter measure particle number concentrations
SMPS - Scanning Mobility Particle Sizers measure particle size distributions

Partisol 2025 sequential air sampler - Ultrapure quartz filters (Pallflex Tissuquartz) are used to allow for the analysis of PM2.5 Elemental Carbon and Organic Carbon (EC/OC).

Leckel SEQ47/50 air sampler. Ultrapure quartz filters (Pallflex Tissuquartz) are used to allow for the analysis of PM2.5 EC/OC.

URG-9000B Ambient Ion Monitor analysers for the measurement of the ionic components of PM2.5 in the atmosphere. The AIM measures SO42-, Na+, NH4+ , Ca2+ , NO3-, K+, Cl- and Mg2+.

ACSM – Aerodyne Aerosol Chemical Speciation Monitor uses established Aerosol Mass Spectrometer technology to provide quantitative chemical composition measurements for organic aerosol, nitrate, sulphate and ammonium.

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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