Measurement and Monitoring of PAHs

11. The then Department of the Environment (DOE) began measurements of PAHs in its Toxic Organic Micropollutants Network (TOMPs) in 1991 (NETCEN, 1998). Seven sites are currently operated. One site is located at a busy roadside in London (Marylebone Road), three are located at urban background sites in London (Victoria Street), Manchester and Middlesbrough, one is a semi-rural site at Hazelrigg (Lancashire) and two are located at rural sites at High Muffles (North Yorkshire) and Stoke Ferry (Norfolk). Eighteen PAHs are measured in the network, listed in the box below, of which those in italics will be discussed further in later sections of this report. This monitoring of PAHs in the national network is limited and it will be noted these sites do not include areas close to point sources.

12. PAHs are present in the atmosphere at low concentrations relative to many other pollutants and they have chemical and physical properties which make their measurement subject to greater uncertainty. Various analytical methods are used and there are reference standards available which calibrate the measurements. In the TOMPs network PAHs are monitored by drawing air through a filter to collect those associated with particles and then through an adsorbent material which collects the gas phase component. The sample consisting of the filter and the adsorbent is then returned to a central laboratory and the PAHs are extracted, separated by either gas chromatography or high performance liquid chromatography and determined with a range of specific detectors.

13. PAHs have been identified in the ambient air of urban areas, in the United Kingdom (NETCEN, 1998). The data suggest that current concentrations of B[a]P in London are more than ten-fold lower than in the era of urban coal combustion (Commins and Hampton, 1976). Table 2 shows concentrations for selected PAHs, measured at a semi-rural and three urban background sites in the TOMPs network. Annual average urban background concentrations of B[a]P in this network ranged from 0.5-0.8 ng/m^3* in 1997. Non-urban levels, as might be expected, are lower and in 1997 were 0.2 ng/m³ at the semi-rural Hazelrigg site. Elevated concentrations of PAHs may be found during pollution episodes and the higher annual average concentrations of the PAHs in Table 2 for 1991 reflect this (Coleman et al., 1997; Jones et al., 1992). Table 3 shows concentrations of these PAHs from short term studies at busy roadsides at Exhibition Road, London and in Copenhagen, Denmark and, for comparison, a remote site in an isolated part of Spitzbergen in the Arctic (Brown et al., 1994; Nielsen, 1995; Berg et al., 1996). In general, for the PAHs in Tables 2 and 3, roadside PAH concentrations are higher than urban background PAH concentrations, which in turn, are higher than rural concentrations, and concentrations in winter are higher than those in summer. The relatively high concentrations observed in Copenhagen (Table 3) reflect the short wintertime monitoring period. The measurements made at Spitzbergen (Table 3) show that some PAHs may be carried for long distances and can be found at detectable concentrations in air in remote locations.

Table 2. United Kingdom ambient concentrations of selected non-volatile PAHs (particulate and gas phase). Measurements summarised from the National Toxic Organic Micropollutants Network. NM = not measured. (NETCEN, 1998)

Table 3. Total (particulate + gas phase) ambient concentrations (ng/m³) of selected PAHs. Measurements summarised from monitoring campaigns undertaken at roadside sites in London and Copenhagen and, for comparison, a remote location in Spitzbergen.

PAH Species	Exhibition Road, London	Copenhagen	Spitzbergen
Benzo[a]pyrene	2.0	4.4	0.009
Benzo[a]anthracene	3.6	4.1
Dibenz[ah]anthracene	0.1		0.002
Benzo[b]fluoranthene	2.1	9.3	0.030
Benzo[k]fluoranthene	2.0
Indeno[123cd]pyrene	2.6	4.5	0.010
Chrysene	5.7	7.9
Monitoring Information
Sampling period	January 1991 - September 1992	January - March 1992	January - December 1995
Author	Brown et al. (1994)	Nielsen (1995)	Berg et al. (1996)

* 1ng/m³ is one billionth of a gram in every cubic metre of air.