Air quality

Review and Assessment of Benzene

Information about air quality in solihull

3 Review and Assessment of Benzene

3.1 The Government has adopted a running annual mean of 16.25µg/m³ (5ppb) as an air quality standard for benzene,

with an objective of meeting that standard by the end of 2003. Given an averaging period of one year, the focus of the review and assessment should be on non-occupational exposures at near ground level outdoor locations, including:-

• Background locations,
• Roadside locations, such as on pavements or close to the facades of buildings,
• Other locations where people may be regularly exposed, such as schools or hospitals.

3.2 Benzene is a aromatic volatile organic compound

consisting of six atoms each of carbon and hydrogen. At normal ambient temperatures it is a liquid, but it readily evaporates and small amounts are detectable in the atmosphere.

Almost all the benzene found in the atmosphere, near ground level in the United Kingdom, is likely to have resulted from human activity.

3.3 The main sources of benzene for non-occupational exposures are petrol-engined vehicle exhausts, petrol refining, evaporation from petrol storage tanks, particularly during refilling, and smoking.

Specific sources of benzene in Solihull are:

• Emissions from motor vehicles,
• Emissions from petrol stations.

Solihull has no significant industrial sources of benzene, so that the relative sources of benzene are those shown in Figure 3.1:

This shows that approximately 99% of the benzene is emitted from road transport related activity.

3.4 Emissions from road transport related activities

include the release of petroleum vapours, when recharging storage tanks at petrol stations and car petrol tanks, tailpipe emissions from motor vehicles and evaporation from petrol storage tanks, particularly in warm weather.

Emissions of petrol vapours when recharging storage tanks at petrol stations and distribution depots are now effectively controlled by the use of vapour recovery systems.

However, emissions from the tailpipes of motor vehicles and evaporation from storage tanks has yet to be controlled effectively.

3.5 National policies

have already reduced the tailpipe emissions of benzene from motor vehicles. Our calculations, based on changing emissions factors, show that the emissions are expected to fall by 70 to 80% between 1996 and 2006, despite an estimated increase in traffic, of between 13.5 to 14.5%, in the West Midlands (Local Transport Plan 2000).

3.6 Benzene Levels in the West Midlands

Benzene is only measured at one location in the West Midlands; the Birmingham East automatic hydrocarbon monitoring station. This station is owned and operated by the Government, as part of the national Hydrocarbon Monitoring Network (HMN).

Figure 3.2 shows how the concentrations of benzene at this station have changed through the 1990s and how they are expected to change through the first five years of the new century.

Trends in West Midlands Air Quality Benzene: Annual Average Values

Figure 3.2

Two studies, using benzene adsorption tubes, have been carried out to check the spatial distribution across Birmingham. The first study, in 1995, indicated that the concentrations of benzene alongside busy roads averaged 14.3µg/m³ (4.4ppb), whilst the background concentrations averaged 4.6µg/m³ (1.4ppb).

Although the second study, in 1999, had a different objective, some of the sites could be compared with the 1995 survey sites. Thus, in this second survey the concentrations of benzene along the busiest road averaged 4.45µg/m³ (1.37ppb), whilst the background concentrations averaged 1.82µg/m³ (0.6ppb).

In both studies the benzene adsorption tubes gave good agreement with the data from Birmingham East automatic hydrocarbon monitoring station.

3.7 Future Trends in Benzene Levels

Government considers that the levels of benzene arising from road traffic and from petrol stations are unlikely to present a significant risk of breaching the standard in 2003.

Measurements of the levels of benzene in the atmosphere around petrol stations, made in Birmingham in 1999, indicate that their opinion is correct.

Since Solihull has no other sources of benzene, there is little risk of the benzene objective being breached.