- Particulate matter (PM10)
Particulate matter (PM) in the air is a priority pollutant internationally due to
its adverse effects on public health as well as its negative effects on sensitive
ecosystems, materials and on climate. Additionally, it is a key contributor to low
visibility incidents.Particulate pollution in the atmosphere derives from a wide
range of sources including transportation of natural materials like sand; dust from
construction activities; traffic and industry. Secondary particles are formed from
atmospheric reactions between gases, such as the photochemical oxidation of sulphur
Airborne particles cover a wide range of sizes. Large particles generally settle
out onto surfaces and cause nuisance effects through soiling of buildings, monuments
and fabrics. Human health concerns are generally centered around fine particulate
matter with an aerodynamic diameter of 10 micrometres (μm) or less, known as PM10.
These particles can penetrate deep into the human respiratory system and are responsible
for a variety of health effects including effects on the respiratory and cardiovascular
systems, asthma and premature death. Health effects of particulate matter are greater
in the presence of high concentrations of SO2, as the two pollutants
- Nitrogen dioxide (NO2)
All combustion processes produce oxides of nitrogen. Nitrogen dioxide (NO2)
is associated with adverse human health effects and is produced mainly through the
atmospheric oxidation of nitric oxide, which is produced during combustion of hydrocarbon
fuels. Sources of nitrogen oxide emissions include road traffic, power stations
Nitrogen dioxide can affect the respiratory system causing inflammation of the airways.
People with asthma or respiratory diseases are particularly sensitive and can show
effects at low concentrations.
- Sulphur dioxide (SO2)
Sulphur dioxide (SO2) is a gas produced from burning fuel and processing
materials which contain sulphur contaminants. Typical sources include oil-fired
power stations, oil and gas processing, industry and road traffic.
Inhalation of sulphur dioxide causes constriction of the airways leading to breathing
difficulties, particularly in those suffering from asthma and chronic lung disease.
SO2 can also lead to the formation of acid rain which can lead to widespread
ecosystem damage in rivers and lakes, sometimes thousands of kilometers from the
original emission source. Direct and indirect impacts on vegetation are also known
to occur at lower concentrations than those affecting human health.
- Carbon monoxide (CO)
Carbon monoxide (CO) is a colourless, odourless gas which is produced by the incomplete
combustion of hydrocarbon fuels. The main source of CO is road traffic, in particular
petrol-engine vehicles. The main threat to human health from carbon monoxide is
from the formation of carboxyhaemoglobin in the blood, which substantially reduces
the uptake and transport of oxygen in the body. People who suffer from existing
diseases which affect delivery of oxygen to the heart and brain (e.g. coronary artery
disease) are at particular risk.
- Ozone (O3)
Ozone (O3) is a secondary pollutant which is formed in the atmosphere
during chemical reactions involving nitrogen oxides, volatile organic compounds
(VOCs) and sunlight. These chemical reactions take place over several hours or even
days, depending on the VOCs present. As a consequence, ozone measured at a particular
location could have been formed from precursor compounds produced hundreds or even
thousands of kilometers away. Once formed, ozone then drifts in the atmosphere under
the influence of meteorological conditions. Maximum concentrations are therefore
generally found some distance downwind from the source emissions. Concentrations
in urban areas with high levels of traffic are often reduced due to the reaction
between ozone and nitric oxide, resulting in the formation of nitrogen dioxide.
Ozone is also toxic to plants and can cause leaf necrosis and affect photosynthesis,
and therefore reducing production of crops and trees.
- Volatile organic compounds (VOC)
Volatile organic compounds (VOCs) is a term given to a wide class of chemical compounds
including aliphatic, aromatic and halogenated hydrocarbons, aldehydes, ketones esters
and amines. They are important in the formation of ozone and can have a variety
of health effects. Some species are directly toxic to humans and some produce offensive
odours at very low concentrations.
- Lead (Pb)
Lead is a naturally occurring metallic element which is found in the atmosphere
as small particles. Industrial sources of lead include battery manufacture and secondary
metal smelting. Road traffic used to be the dominant source of lead in urban areas,
as it was used as an additive in petrol. In recent years, its use in petrol has
been phased out and this is no longer a major source.
Exposure to lead can have a variety of human health effects, including effects on
the synthesis of hemoglobin, effects on the kidneys, gastrointestinal system and
effects on the nervous system. It has also been shown to have a negative effect
on childhood neurological development.