Polycyclic Aromatic Hydrocarbons (PAH)


The polycyclic aromatic hydrocarbon (PAH) Network, which has operated since 1991, currently monitors the ambient concentrations of PAHs in the UK atmosphere by sampling PAHs at 31 sites across England, Wales, Scotland and Northern Ireland. The PAH Network has strong links with the Toxic Organic Micro Pollutants (TOMPs) Network, which monitors at fewer sites – six in total. Three of these TOMPs sites also provide samples to be analysed for the PAHs allowing the assessment of PAHs at 34 sites. The background monitoring sites at Auchencorth Moss and Harwell provide data to ensure the UK complies with the EMEP monitoring requirements.

What is measured?


Polycyclic aromatic hydrocarbons (PAHs) are a group of persistent organic compounds, some of which are toxic and/or possible or proven human carcinogens; they are produced via incomplete combustion of carbon containing fuels from industrial, commercial, vehicular and residential sources.

The following species are measured in the Polycyclic Aromatic Hydrocarbon Network:

PAHs 2-methyl napthalene, 1-methyl napthalene, biphenyl, acenaphthylene, acenaphthene, fluorene, phenanthrene, anthracene, 2-methyl phenanthrene, 2-methyl anthracene, 1-methyl anthracene, 1-methyl phenanthrene, 9-methyl anthracene, 4.5-methylene phenanthrene, fluoranthene, pyrene, retene (1-methyl-7-isopropylphenenthrene), benzo[c]phenanthrene, benzo[a]anthracene, chrysene, cyclopenta[c,d]pyrene, benzo[b]naph[2,1-d]thiophene, 5-methyl chrysene, benzo[b + j]fluoranthenes, benzo[k]fluoranthene, benzo[e]pyrene, benzo[a]pyrene perylene, indeno[1,2,3-cd]pyrene, dibenzo[ah + ac]anthracenes, benzo[ghi]perylene anthanthrene, dibenzo[al]pyrene, dibenzo [ae]pyrene, dibenzo[ai]pyrene, dibenzo[ah]pyrene, coronene and cholanthrene.

What is the purpose of the network?

There are three major policy drivers and data uses for this programme:

  • The European Community's fourth Air Quality Daughter Directive (2005/107/EC), specifies a target value of 1 ng m-3 for the annual mean concentration of benzo[a]pyrene as a representative PAH, to be achieved by 2012.
  • The UK Air Quality Objective for PAHs, based on the recommendations of the Expert Panel on Air Quality Standards (EPAQS), is for a maximum annual air concentration of 0.25 ngm-3 benzo[a]pyrene.
  • The UNECE protocol on Persistent Organic Pollutants (POPs), which includes PAHs. Under the protocol, there is a requirement for signatories to control emissions of PAHs to measure and assess the long-range transport of four specified PAHs.

All of these policy imperatives require data on ambient concentrations and trends of PAHs in the environment.

How is the network run?

Prior to 2007 the network used Andersen GPS-1 pesticide samplers to sample PAHs in ambient air. The network sampler was changed to a Digitel DHA-80 high volume PM10 aerosol sampler (operating with 1 day sampling period) in order to comply with the requirements of the 4th Air Quality Daughter Directive.

At all the PAH network sites, PAHs associated with particles are captured on glass fibre filters. Additionally, two sites (Auchencorth Moss and Harwell) also use a modified DHA-80 high volume sampler; this sampler captures both gas and particle-phase PAHs on glass fibre filters and polyurethane foam (PUF) absorbents. At these two sites PAH deposition samples are also collected.

Extraction of the filter and, where relevant, foam media and subsequent analysis by gas chromatography/mass spectroscopy (GC/MS) provides data on the ambient concentrations of 39 PAH species. The deposition method, TOMPS and the PUF samplers measure the same list of compounds, but are subject to a high degree of uncertainty.

View data for sites in this network

PAH data is available on the Polycyclic Aromatic Hydrocarbon (PAH) Data page.

Annual PAH network reports can be found in the library section of this website.

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