Main air
pollutants
The air that we breathe consists
of approximately 78.1% nitrogen and 20.9% oxygen with about 0.036%
carbon dioxide. The pollutants that we are concerned about are
generally measured in parts per million (ppm) or parts per billion
(ppb).
For a comparison, 1 ppm in percentage terms is 0.0001%.
The government has a national air quality strategy to deal with air
pollution and has identified eight pollutants of particular concern
with regard to human health.
If you have lung problems or are particularly sensitive, the type
and level of pollution you are exposed to may cause an effect, as
described below. In addition to health effects, air pollution can
also affect the environment surrounding us; which may include
discoloration and erosion of buildings and minimised vegetation
growth in city areas, the green house effect and global warming and
acidification of water ways.
Ozone is a 'secondary pollutant' in that there is
no process that produces ozone itself, it is actually formed by the
action of sunlight on polluted air.
Carbon monoxide is a colourless odourless gas
that is produced by the incomplete combustion of any fuel that
contains carbon. It use to be a major constituent of exhaust from
petrol engines, however, as vehicle technology has improved, there
is less in the exhaust. It was estimated that in 1996, 97% of
carbon monoxide in London was from vehicles mainly with petrol
engines. As its effect is to reduce the blood's capacity to carry
oxygen around the body, it is highly toxic and can be fatal at high
doses and in confined areas. It can starve the brain and other
vital organs such as the heart of oxygen, worsening conditions
relating to particular organs.
Benzene is an ingredient of petrol. It can also
be formed in a petrol engine whilst it is running. Approximately
70% of all benzene emissions come from this source. Benzene is a
carcinogen and has been linked with leukaemia.
1,3 Butadiene is formed whilst a petrol engine is
running (there is little or no 1, 3 Butadiene in petrol itself). 1,
3 Butadiene is a carcinogen.
Lead was once widespread in petrol in the form of
tetra-ethyl lead, an 'anti-knock' additive. Levels of atmospheric
lead were once very high, principally from this source. Lead is
also a major ingredient used in many industrial processes,
principally in the production of batteries. Lead causes toxic
effects even at low levels of exposure. It can interfere with the
development of the nervous system and damages haemoglobin
production in the blood. Since 2000, lead has no longer been added
to petrol. In addition there are strict controls on the emission of
lead from industry.
Sulphur dioxide in the air is derived mainly from
the use of fuels that contain sulphur as a contaminant. In the
past, the major source of sulphur dioxide has been from domestic
coal fires. With the advent of the Clean Air Act and the move to
smokeless fuels for domestic heating such as gas, the major source
of atmospheric sulphur dioxide is from electricity generation
(approximately 70% nationally). In London however, diesel vehicles
produce about 20% of emissions. Sulphur dioxide is an irritant gas
which affects the airways of the lungs when inhaled, increasing the
symptoms of those suffering from lung diseases. This gas may also
irritate the eyes.
Nitrogen dioxide is formed as part of the
combustion process. As described above, atmospheric air consists of
about 80% nitrogen gas (which is harmless) and 20% oxygen. As air
is burnt, some of the nitrogen gas is converted to nitric oxide
(NO) which is also harmless. After nitric oxide is released to the
atmosphere is then oxidised to nitrogen dioxide. Nitrogen dioxide
is an irritant gas which effects the lungs. In London, road traffic
contributes about 75% of the nitrogen dioxide in the air. Nitrogen
dioxide is an irritant gas which affects the airways of the lungs
when inhaled, increasing the symptoms of those suffering from lung
diseases. This gas may also irritate the eyes.
Fine particles are not a discrete chemical,
rather they are the very fine particles of soot that can sometimes
be seen in the exhaust of a badly maintained vehicle. They are also
known as PM 10, which is a measure of their size, which is less
than 10 microns in size (a micron is one millionth of a metre). The
importance of the size is that these particles can penetrate deep
into the lungs where the body finds it difficult to get rid of
them. As fine particles are not an individual chemical, they can
originate from many different sources. In London, road transport is
the dominant source of fine particles. Apart from vehicles, fine
particles can come from other sources such as combustion,
construction and demolition work, soil and dried salt particles
from the seaside. Due to their size, small particles such as PM10,
can be carried deep into the lungs when inhaled. Once in the lung,
the particles can cause inflammation and a worsening of symptoms
relating to lung diseases.