This Network measures ambient levels of arsenic, cadmium, chromium, cobalt, copper, iron, manganese, nickel, lead, platinum, selenium, vanadium, zinc, and mercury, in particulate matter, at 25 sites around the UK. Vapour phase mercury is also measured at 13 sites. Accurately measured concentrations of the most toxic metals: arsenic, cadmium, nickel, mercury and lead are requirements of the new EC Air Quality Directive and the Fourth Air Quality Daughter Directives. Sites are predominantly located downwind of large metals processing facilities and in centres of population.

Particulate samples are taken using Partisol 2000 instruments (fitted with PM₁₀ heads), for a period of one week, onto filters. Vapour-phase mercury sampling takes place by pumping air at a constant rate through gold-coated silica absorption tubes.

Analysis for particulate-phase metals is carried out at NPL by ICP-MS. Analysis of vapour-phase mercury samples takes place at NPL by thermal desorption and atomic fluorescence. Both procedures are UKAS-accredited. More information on the operation of the Network is described in the publications listed below:

• 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

Location of sites on the UK Heavy Metals Monitoring Network
(image courtesy of Defra)