National Physical Laboratory

Heavy Metals Monitoring Network

Some heavy metals are known to be toxic and carcinogenic. They are emitted during industrial processes and through the abrasion and degradation of metal-containing materials. Heavy metals are present in the air in particulate matter (PM) and, in the case of mercury, also in the vapour phase.

European legislation limits the maximum allowable ambient concentrations of lead, nickel, arsenic, cadmium and mercury in ambient air. Member States are required to make regular measurements of these metals in order to assess compliance. In the UK, there are 25 monitoring sites, some of which are situated near industrial sources, others which are sited in areas of large population, and other which monitor roadside locations. Since 2004, NPL has operated the UK Heavy Metals Monitoring Network on behalf of the UK Department for Environment, Food and Rural Affairs. NPL uses UKAS accredited procedures to analyse samples collected by the monitoring network.

UK Heavy Metals Monitoring Network

Location of sites on the UK Heavy Metals Monitoring Network
(image courtesy of Defra)
PM10 Sampler
PM10 Sampler at Eskdalemuir

Particulate Measurements

Low volume air samplers are used to collect PM10 (particulates with an aerodynamic diameter of less than 10mm) onto cellulose filters.

Filters are totally digested in an acidic matrix at high temperatures using a microwave. The digested sample is diluted with deionised water and analysed by Inductively Coupled Plasma-Mass Spectrometry (ICP-MS). The suite of metals measured for by the UK Defra Heavy Metals Monitoring Network is:

V     Cr     Mn     Fe     Ni     Cu     Zn     As     Cd     Pt     Hg     Pb     Se     Co

Concentrations of these metals in ambient air are typically very low, ranging from a few pg.m-3 in the case of Pt, to a few of μg.m-3 for Fe.

Mercury Vapour Measurements

Vapour phase mercury is sampled onto adsorption tubes using a low volume pump (see figure below). The air is passed through a filter to remove particulates before entering the tube, where it is adsorbed onto gold-coated silica. NPL uses a Sir Galahad atomic fluorescence spectrometer ( to thermally desorb and measure the mercury collected on the adsorption tubes.

Sampling Train for Vapour Phase Mercury
Diagrammatic representation of the sampling train for vapour phase mercury


  • Interlaboratory comparison exercise for the determination of As, Cd, Ni and Pb in PM10 in Europe
    Gerboles, M; Brown, R J C; et al
    Atmospheric Environment, 2011, 45, 3488-3499
  • Comparison of estimated annual emissions and measured annual ambient concentrations of metals in the United Kingdom 1980-2007
    Brown, R J C
    Journal of Environmental Monitoring, 2010, 12, 665-671
  • Twenty-five years of nationwide ambient metals measurement in the United Kingdom: concentration levels and trends
    Brown, R J C, Yardley, R E, Muhunthan, D, Butterfield, D M, Williams, M, Woods, P T, Brown, A S, Goddard S L
    Environmental Monitoring and Assessment, 2008, 142, (1-3), 127-140
  • Accurate calibration of mercury vapour measurements
    Brown, R J C, Brown, A S
    Analyst, 2008, 133, 1611-1618
  • Establishing SI traceability for measurements of mercury vapour
    Brown, A S, Brown, R J C, Corns, W T, Stockwell, P B
    Analyst, 2008, 133, (6), 946 - 953
  • On the Optimum Sampling Time for the Measurement of Pollutants in Ambient Air
    Brown, R J C, Hood, D, Brown, A S
    Journal of Automated Methods and Management in Chemistry, 2008, Volume 2008, Article ID 814715, 6 pages
  • A practical uncertainty budget for ambient mercury vapour measurement
    Brown, R J C, Brown, A S, Yardley, R E, Corns, W T, Stockwell, P B
    Atmospheric Environment, 2008, 42, (10), 2504-2517
Last Updated: 27 Oct 2014
Created: 2 Aug 2007


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