Benzene and 1,3-butadiene concentrations at the roadside - Introduction
1 Introduction
Over the last 10 years the issue of urban air pollution has become a major factor driving environmental legislation within the European Union and the United Kingdom. An extensive programme of urban air monitoring has been established in the UK, and health based air quality standards, and targets for improvement, have been set.
Part IV of the Environment Act, 1995, establishes a national framework for air quality management, and requires all local authorities in Wales and Scotland and London borough, district and unitary councils in England to conduct local air quality reviews. Where the reviews indicate that objectives set out in the Air Quality Regulations, 1997, will not be met by 2005, the relevant authority is required to designate an Air Quality Management Area. Further work is then required to investigate ways to ensure compliance of the area by 2005. Accurately predicting the extent to which current concentration levels will have decreased by 2005 is thus fundamental in achieving the aims of the National Air Quality Strategy (NAQS).
The NAQS gives the following objectives for benzene and 1,3-butadiene, to be reached by 2005:
Benzene:
The maximum annual running mean must not exceed 5 ppb
1,3-Butadiene:
The maximum annual running mean must not exceed 1 ppb
In addition, a target value of 1 ppb for benzene (expressed as an annual running mean) has been set by EPAQS (Benzene- EPAQS 1994).
There are two primary sources of Volatile Organic Compounds (VOCs)- emissions from road transport and industrial activities. As part of the local authority reviews several "pilot studies" have already been conducted to investigate benzene concentrations in the vicinity of major industrial installations. However, in the urban environment emissions from road transport are usually the primary source of both benzene and 1,3-butadiene.
Several measures have already been introduced to reduce the emissions of pollutants from the road transport sector. The current trend, of decreasing annual emissions of benzene and 1,3-butadiene has primarily been caused by the introduction of catalytic converters for cars (Directive 91/441/EEC) and a further directive implemented in 1996 (94/12/EEC). Other measures include the introduction of carbon canisters to reduce evaporative emissions and the introduction low benzene fuel.
This report investigates the current and predicted concentrations of benzene and 1,3-butadiene at locations likely to be dominated by the emissions from road transport- roadside and urban background locations.
The methodology for estimating current and future benzene and 1,3-butadiene roadside concentrations is described in Section 4 and outlined below:-
Maps of current background concentrations have been calculated from a combination of emission inventories and ambient measurements. This is discussed in Section 2
Current roadside benzene and 1,3-butadiene measurement data have been examined to determine the relationship between the "roadside enhancement" of concentrations and vehicle emission estimates. This is discussed in Section 3.
Current roadside concentrations throughout the UK have been estimated from the sum of background concentrations and this enhancement.
Future roadside concentrations have been predicted by applying emissions reductions to the modelled roadside concentrations.
Predictions of benzene and 1,3-butadiene concentration have also been made, for 2005, at the urban background locations on the UK Hydrocarbon Monitoring Network. Several emission reduction scenarios have been used to investigate the potential reductions of concentration.
Conclusions and results from this study are used to indicate whether compliance with the Air Quality Regulations is likely to be met on a national level (Section 5). In addition, the potential for compliance with the target value for benzene, by 2010, has been investigated. Results are reported in Section 4.
Concentrations of benzene, 1,3-butadiene and NO
x are expressed as either ppb or µg m-3 in this report as appropriate. Final results are generally expressed in ppb for comparison with the NAQS objectives; while some intermediate calculations are best expressed in terms of µg m-3 since this enables ratios of concentrations and emissions of different pollutants to be compared directly.
The following conversion factors have been applied:-
