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Polycyclic Aromatic Hydrocarbon results - diffusion tube sampling

Polycyclic Aromatic Hydrocarbon (PAH) was monitored in the Borough from 1991 to 2006, at roadside locations as part of the London-Wide PAH survey.

Polycyclic Aromatic Hydrocarbon (PAH) Results

As PAH levels tend to vary seasonally, readings were until 1997, taken twice a year, once in summer and once in winter in order to allow a comparison of any such variation. However since 2001 PAH is monitored over a 2 week period in a month, every month. The historical reports although are London wide reports only contain monitoring information relevant to the Richmond Borough.PAH monitoring ceased in 2006 as levels were consistently below the limit.

London Wide Environmental Programme annual reports

The primary aim of the London Wide PAH survey is to make an assessment of the exposure of the London population to PAH's. The data from this survey has been compared with guidelines of PAH's and with results of other PAH surveys around the UK, in order to increase the understanding of the scale of the pollution problem posed by PAH's in London.

The risk is expressed as Benzo (a) pyrene B(a)P rather than PAH because it is the best known carcinogen in the PAH group and B(a)P is the only PAH for which there are any authoritative recommendations as to an appropriate guideline or standard. Hence the annual average concentration of B(a)P is used as a marker for PAH.

The reports contains information of the sources of PAH, guidelines, the measurement programme and results. All the results are measure in nanograms per metre cubed (ng/m-3).

PAH results

The following results represents the raw sampling data for the borough. From 1995 to 1997 the results are shown as summer and winter, however from 2001 onwards the monthly results are given. We do not have a breakdown of the 1991 to 1994 results.

From 1991 to 1997 there were no UK guidelines for PAHs so the results were compared against the United States Environmental Protection Agency guideline value of 1ng/m-3.  However we now use the UK 2010 air quality objective of 0.25ng/m-3 The more recent monitoring results show that apart from 2001 to 2002 the results complied with the UK 2010 objective.

PAH graphs

The graphs below show the annual average for both total PAH and B(a)P and the summer / winter average for total PAH from 1991 to 2007.

Updated: 25 February 2021

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