- Introduction
There are a number of sources of benzene emissions to the atmosphere in the UK. The principal source of emissions is petrol engine exhausts, which account for more than 78% of the UK total. By contrast, emissions from the petroleum refining and distribution industry are relatively small, at around 3% of the UK total, but nonetheless these emissions are of potential concern in terms of exposure to members of the public who live and work in the vicinity of petrol filling stations.
Emissions from petrol stations are associated with a number of sources:
- Displacement of the headspace vapour from the underground storage tanks when road tankers are refilling the tanks. The mass emission rate will be relatively high, but only during the short periods of refilling.
- Displacement of the headspace vapour from the tank of the car as it is refuelled. The mass emission rate will be much lower than above but vapour will be emitted continuously throughout the period of opening.
- Evaporative losses from the car fuel system whilst it remains parked. These emissions are expected to be relatively low.
In order to reduce emissions of VOCs, including benzene, at petrol filling stations, a number of initiatives have been introduced, or are time-tabled for implementation in the future. The prevention of emissions during storage tank refilling is termed Stage IB Vapour Recovery, and employs systems to ensure that the displaced vapours are recycled back into the road tanker. An EU Directive (94/63/EC) concerning Stage I controls was adopted on 1 January 1995, and is to be implemented in a staged fashion, with all new service stations being equipped with effect from 1 January 1996, and existing stations being retrofitted with controls according to a timetable up until 2005, depending upon the throughput of the station.
An EU Stage II Directive is currently being prepared which covers emissions during refilling of vehicles, which can be prevented by fitting recycling devices to the petrol nozzle. The House of Commons Select Committee on the Environment recently reported on Volatile Organic Compounds, and recommended that Stage II controls be fitted ahead of the deadline proposed within the EU Directive. In order to assess the implications and effectiveness of this recommendation it is necessary to acquire a fuller understanding of benzene levels in and around petrol filling stations. The requirement for such information forms the basis of this study which has been commissioned by the Department of the Environment.
The objective of this study, which was intended as a pilot exercise, was to assess ambient levels of benzene in the immediate vicinity of selected petrol stations in the Greater London Area. The results are compared with relevant air quality standards set in the Consultation Draft of the National Air Quality Strategy (NAQS), and measured levels are assessed in terms of implications for human health. The data are also compared with results previously reported within other studies
Report prepared by Stanger Science and Environment
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