Measurement and Monitoring of 1,3-Butadiene

6. In contrast to the better known pollutant gases, there is relatively little information on levels of 1,3- butadiene in the ambient air of the United Kingdom. The first measurements were made only in 1990, on the Norfolk coast and in Cumbria, and between mid 1991 and mid 1992 continuous hourly measurements were made at a roadside site in central London. The Department of the Environment is now establishing a network of 12 automatic gas chromatography sites around the country where continuous monitoring of 1,3-butadiene (measuring to an accuracy of +/-10% and a precision of O.l ppb¹) and other hydrocarbon compounds will take place. Sites have been established in Middlesbrough, London Eltham, London Bloomsbury, Belfast, Edinburgh, Birmingham, Bristol, Cardiff and a site in Leeds is expected to be operational shortly. Thus daily dissemination of information to the public on 1,3-butadiene levels through the Department of the Environment's Air Quality Bulletin is now possible.
7. Table 1 summarises the available monitoring data for 1,3-butadiene in the United Kingdom since monitoring began in 1990. The measurements have shown a very close correlation between 1,3-butadiene and other pollutants, such as carbon monoxide, oxides of nitrogen and benzene. These relationships are illustrated in Figures l and 2. The average annual levels to which the population of the United Kingdom is exposed clearly depend on proximity to motor traffic (see Table 1). Thus someone living close to a busy road may be exposed to an annual average concentration of about 0.7 ppb, whereas someone living on the Norfolk coast may be exposed to around 0.04 ppb. The very striking difference between urban and rural sites reflects not only differences in traffic density but also the fact that 1,3-butadiene is removed from the atmosphere in a matter of hours by chemical reactions. These prevent it being dispersed far from its source. On the basis of the data in Table 1 and analysis of the relative concentrations of a number of motor vehicle- derived pollutants measured simultaneously at Cromwell Road and Exhibition Road in London, it is unlikely that annual average 1,3-butadiene concentrations will exceed 1 ppb close to the most heavily trafficked roads in the United Kingdom.

Table 1 Ambient concentrations of 1,3-butadiene in the United Kingdom

Site	Location	Average Concentration (ppb**)	Period of measurement
Exhibition Road, London	Urban roadside*	1.09	July 1991-December 1991***
		0.63	January 1992-June 1992
		(0.86	July 1991-June 1992***)
Bloomsbury, London	Urban roadside*	0.32	February 1993-December 1993
Eltham, London	Urban baseline	0.21	August 1992-March 1994
Middlesbrough	Urban baseline	0.35	January 1992-December 1992
		0.45	January 1993-December 1993
Belfast	Urban baseline	0.65	August 1993-March 1994
Birmingham	Urban baseline	0.41	August 1993-March 1994
Cardiff	Urban baseline	0.60	November 1993-March 1994
Edinburgh	Urban baseline	0.24	October 1993-March 1994
West Beckham, Norfolk	Rural	0.04	January 1990-March 1991
Great Dun Fell, Cumbria	Remote rural	0.01	January 1990-March 1991
* Urban roadside locations are away from the immediate influence of traffic, 5 metres from the kerbside with a sampling inlet 3 metres above the pavement. ** All provisional data (ie. not ratified by national quality assurance/quality control procedures) *** This period includes the December 1991 pollution episode mentioned in the text of the Report.

8. These very low annual average concentrations do, of course, conceal fluctuations caused by combinations of traffic and weather conditions, and short term higher concentrations may occur. For example, during December 1991 heavy motor traffic at a time of very cold still weather produced a pollution episode during which high levels of all exhaust-derived pollutants were measured in central London. During this episode, the hourly average 1,3-butadiene level remained close to 10 ppb (see Figure 2). The highest hourly level, of 30 ppb, had been recorded a few days earlier. Sporadic peaks of 1,3- butadiene have been observed at some of the urban baseline sites in Table 1. Their origins have yet to be established but they point to there being some potentially significant industrial sources of 1,3-butadiene. Such intermittent sources are unlikely to contribute significantly to annual average concentrations.
9. There is no evidence that petrol contains anything other than trace quantities of 1,3-butadiene, so petrol evaporation is unimportant as an urban source of 1,3-butadiene. Exhaust emissions are the only urban source which has so far been quantified in the United Kingdom. Vehicles equipped with three-way catalytic converters emit negligible quantities of 1,3-butadiene and offer a reduction in emissions over those produced by non-catalyst cars of at least a factor of twenty. Emissions from diesel cars are detectable at about one tenth of those of noncatalyst cars but emissions of 1,3-butadiene are higher from diesel cars than from cars equipped with three-way catalytic converters. The fitting of oxidation catalysts to diesel cars to meet future emission requirements would, however, lead to a reduction of diesel emissions of 1,3-butadiene. It is likely therefore that urban 1,3-butadiene levels will decline dramatically as non-catalyst cars are phased out in the future and that this decline will not be hindered significantly by increased urban traffic growth.
10. The Panel, in deciding upon a recommended Standard, have considered the time period over which 1,3- butadiene measurements should be made. As is discussed in the next section, 1,3-butadiene has the potential to cause leukaemias and lymphomas. At concentrations occurring in the ambient atmosphere, 1,3-butadiene does not have short-term, or acute, effects. The risk of developing cancer is related to the period of exposure and the concentration to which the person is exposed.
11. The Panel therefore consider it appropriate to recommend a Standard based on a running annual average concentration², since this is likely to best reflect the integrated exposure of the population. The Standard is set on the basis of possible health effects; it is intended that techniques for its monitoring be consistent with those of the Department of the Environment's Enhanced Urban Network. Such an average will tend to obscure individual high concentrations recorded on a daily basis, although pollution episodes such as that of December 1991 in London will still be apparent.
12. In discussing the recommendation of an Air Quality Standard, the Panel have had in mind the importance of practical measures to ensure compliance. As stated above, the most important of these relate to traffic exhaust emissions. Whilst the Government has already implemented a number of important measures in this direction, there also remains much that individuals can do. Since traffic levels are predictable and since tomorrow's weather conditions can be forecast increasingly accurately, it is possible to estimate the likely atmospheric concentration of 1,3-butadiene and other pollutants the day before they occur. This means that episodes, such as that in December 1991, may be forecast and the public informed of action that could be taken to reduce such levels, and thus reduce the population's lifetime exposure. For example, by restricting the use of motor vehicles at these times it is possible to contribute to reducing the severity of such episodes.

²    The hydrocarbon analyser utilised in the Department of the Environment's national network collects and analyses samples once per hour. The running annual average concentration is calculated by averaging all appropriate available hourly values.