Benzene is a known human carcinogen. Some 98% of emissions in the UK arise from vehicle exhausts and evaporation from petrol refining, distribution and vehicle fuelling.
In February, the Government's Expert Panel on Air Quality Standards (EPAQS) proposed an AQS of 5ppb as a running annual average. Because of benzene's carcinogenic properties, the panel also urged the Government to set a deadline for reducing the AQS to 1ppb (ENDS Report 229, pp 4-5 ).
The Government has yet to respond to the EPAQS report. But in October, the House of Commons' Transport Committee gave credence to claims put forward by lead additives manufacturer Associated Octel that the use of unleaded fuel in cars without catalysts increases benzene emissions (ENDS Report 237, pp 26-27 ).
On 27 October, Mr Atkins refuted Octel's claims in a parliamentary answer. And he went on to say that "benzene levels in the UK are below the 5ppb level recommended to the Government by EPAQS, and are likely to fall as more catalyst-equipped cars enter the national fleet."
In similar vein, the UK Petroleum Industry Association has claimed that "the 5ppb objective is virtually achieved already". It says that measures already under way - principally the introduction of catalysts - will reduce benzene emissions "by as much as 40% in six years."
In February, ENDS reported that many councils had detected benzene at levels above the proposed standard. Some of the high readings had been taken with Opsis open-path spectrometers, which are of dubious accuracy for benzene measurements. However, high levels recorded by diffusion tube tests have now been confirmed by monitoring carried out for seven London boroughs by the environmental consultancy TBV Science.
During 1993, TBV carried out sampling over a series of two-week periods at 20 "background" sites. These were more than 40 metres from busy roads in residential areas and school playgrounds. Average benzene levels over the year ranged from 1-9ppb - but over one-quarter of the sites exceeded the proposed 5ppb standard. Provisional results for 1994 show a similar pattern.
EPAQS recommended that "techniques for monitoring the standard be consistent with those of the Department of the Environment's Enhanced Urban Network (EUN)." The only occasion on which the EUN site has recorded an annual mean benzene level of over 5ppb was when the effects of the severe December 1991 pollution episode in London were included.
To confirm the accuracy of its method, TBV placed diffusion tubes beside EUN sites at Eltham and Bloomsbury in London, and also one in Birmingham. The techniques showed a fairly close correlation, recording similar benzene levels of only 1-3ppb - raising awkward questions about the location of the DoE's monitoring sites.
During 1993, TBV also conducted tests at 12 sites within 20 metres of the kerbside of busy roads. Annual mean benzene levels ranged from 3ppb to over 20ppb. The 5ppb level was exceeded at seven sites.
Finally, tests were carried out beside two petrol stations, where significant emissions can arise from fuel handling, distribution and storage. One site recorded an annual mean of 14ppb. The other recorded a mean benzene concentration of only 4ppb - but the station involved is believed to have fitted vapour recovery equipment during 1993.
TBV is now working with 13 London boroughs, and is carrying out tests at 62 sites in the capital. Each test costs £35-£45. TBV's air quality consultant Dr Sally Uren says that the technique "gives results as accurate as those obtained by more sophisticated and more expensive methods."