Traffic, its impacts and public attitudes - Transport Policy and Planning in Great Britain - page 51

street lighting, especially on main roads in rural areas, is an associated phenomenon
which is eroding the remaining areas from which it is possible to see a dark night sky.
3.6 Local air pollution
Transport is the source of a number of air pollutants (Box 3.1). Mostly these are of
concern because of their damage to health. However nitrogen oxides and sulphur
dioxide also contribute to the formation of ozone which is a harmful secondary
pollutant and a greenhouse gas. Concentrations of pollutants from motor vehicles are
also perceived as smell and smoke which are particularly unpleasant when experienced
at close quarters by pedestrians and cyclists.
The significance of transport as a share of emissions from all sources and in terms
of volume is depicted in Figure 3.8. Transport is the main source of 1,3-butadiene but
carbon monoxide, nitrogen oxides and particulates are currently the most significant
in terms of volume.
Dramatic reductions have been achieved in the volume of emissions since 1990
through a series of progressively tighter standards set under EU regulation. The
requirement to install three-way catalytic converters in all new petrol-engined cars
from 1993 represented a reduction of 90% or more in emissions of carbon monoxide,
hydrocarbons and oxides of nitrogen from these vehicles. At the same time the
installation of traps on diesel-engined cars and vans reduced their emission of
particulates by about two-thirds. Progress with buses and HGVs (which have much
higher emission levels of particulates and oxides of nitrogen) has been slower but the
Euro III standards applied in 2002-05 represent a reduction of between a half and a
third compared with pre-1993 levels.
Box 3.1 Nature and effects of pollutants from transport
• 1.3-butadiene: Mainly from combustion of petrol. Carcinogenic.
• Carbon monoxide: Formed from incomplete combustion of carbon-containing
fuels. Reduces capacity of blood to carry oxygen to body cells; people with
existing diseases affecting delivery of oxygen to heart or brain (e.g. angina)
particularly at risk.
• Oxides of nitrogen: Produced by combustion in air. NO2 enhances the response
to allergens in sensitive individuals; at high levels causes inflammation of airways.
Contributes to formation of secondary particles and ground level ozone; damages
vegetation.
• Particulates: Particles derived from engine emissions, tyre and brake wear.
Exposure associated with respiratory and cardiovascular illness and mortality.
• Benzene: Derives from combustion. Carcinogenic.
• Sulphur dioxide: Derives from combustion of fuels containing sulphur [now mainly
coal and heavy oils]. Causes constriction of the airways of the lung; particularly
affects people suffering from asthma and chronic lung disease.
• Lead: [Emissions now conined to the combustion of coal, iron and steel.]
Exposure to high levels may result in toxic biochemical effects.
From Defra Air Quality Strategy 2007 Table 1