The objective of this network is to monitor a range of toxic organic micropollutants - shown below - at selected sites around the UK. The samples are collected over two weeks, bulked together and then chemically analysed every 3 months for PAH's and every 6 months for dioxins.

The major source of these compounds in ambient air is the incomplete combustion of carbon based fuels - hence industrial plant and motor vehicles produce the largest quantities. In terms of personal exposure, however, cigarette smoke also contains significant concentrations of PAH.
Many of them are confirmed or suspected carcinogens.

Their chemical structure is of a number of benzene rings fused together - thus giving a large range of possible compounds. One of these, benzo(a)pyrene, is illustrated below.

In this programme, a selected suite, as identified by WHO, are measured, as shown in the introductory table.

PCB's

These compounds can be produced when a chlorine containing substrate is burnt - hence domestic waste containing PVC can be a source of these materials. They are also used in electrical transformers.
Their structure is of two linked benzene rings, each ring having a number of chlorine atoms on it. As with the PAH's, this gives a large range of possible species, of which a few are selected for measurement. By convention, each isomer is given a number - as an example, the structure of PCB 61 is shown below.

The structures of all the measured PCB's are given in the A-Z of Air Quality.

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Dioxins (and furans)

Again this is a class of compounds, of which a suite has been chosen for measurement. Their structure is of two benzene rings, linked by two bridging oxygen atoms (one for the furans). The benzene rings have a varing number of chlorine atoms attached to them, giving the potential for a range of structures.The structure of 2,3,7,8-tetrachlorodibenzo-dioxin is shown below.

Further information about the structures of these compounds can be found in the A - Z of Air Quality.

Monitoring Sites

There are a total of 18 sites for which data is available. Three of these (Cardiff, London 1 and Stevenage) are no longer operating. Details of these are given below.

Site	Analytes	Site Type	OS Grid Reference	Start Date	End Date	Forecast Region	Environment Agency Region
Ashington	PAHs	urban	NZ272 878	Feb 1999	ongoing	North East	North East
Bolsover	PAHs	urban	SK 469 726	Feb 1999	ongoing	North East	North East
Cardiff	PAHs, PCBs, PCDD/Fs	urban	ST183172	Jan 1991	1994	Wales	Welsh
Glasgow	PAHs	urban	NS595654	May 1999	ongoing	Scotland	Scotland
Hazelrigg	PAHs, PCBs, PCDD/Fs	semi-rural	SD493578	Sept 1992	ongoing	North West	North West
High Muffles	PAHs, PCBs, PCDD/Fs	rural	SE776939	Jan 1997	ongoing	North East	North East
Holyhead	PAHs	urban	SH2468 826	Feb 1999	ongoing	Wales	Welsh
Kinlochleven	PAHs	urban	NN186 620	Feb 1999	ongoing	Scotland	Scotland
Lisburn	PAHs	urban	vJ286 675	May 1999	ongoing	Northern Ireland	Northern Ireland
London 1	PAHs, PCBs, PCDD/Fs	urban	TQ301792	Jan 1991	March 1998	London	Thames
London 2	PAHs, PCBs, PCDD/Fs	urban	TQ293171	Sept 1998	ongoing	London	Thames
Manchester	PAHs, PCBs, PCDD/Fs	urban	SJ834982	Jan 1991	ongoing	North West	North West
Middlesbrough	PAHs, PCBs, PCDD/Fs	urban	NZ505194	April 1993	ongoing	North East	North East
Newport	PAHs	urban	ST355880	Feb 1999	ongoing	Wales	Welsh
Port Talbot	PAHs	urban	SS780882	Feb 1999	ongoing	Wales	Welsh
Scunthorpe	PAHs	urban	SE905107	Feb 1999	ongoing	North East	North East
Stevenage	PAHs, PCBs, PCDD/Fs	urban	TL237225	Jan 1991	April 1992	South East	Thames
Stoke Ferry	PAHs, PCBs, PCDD/Fs	rural	TL 700988	Feb 1997	ongoing	East Anglia	Anglian

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