Some common air pollutants

Air pollution consists of a number of natural and man made particles and gases that are released into the atmosphere. The overall characteristics and behaviour of each pollutant is different and therefore the understanding of their interactions is limited.

Meteorological conditions can either aid or hinder the dispersion of the pollution. During wet or windy conditions, levels are generally low as they are either blown away and reduced to harmless quantities or they are removed from the air by rain. Temperature inversions, where warm air traps cooler air below, will cause the pollution to remain in the area, possibly at high levels.

 

Everyday we are exposed to a large number of different particles that are present in the atmosphere all around us. The way that particles act depends on their size. Large particles do not stay in air for very long before they are deposited close to their source. They are unlikely to be inhaled. Smaller particles can be carried long distances and because they are smaller they may be inhaled.

PM10 are particles that are less than 10 microns in size where as PM2.5 are finer particles with a diameter less than 2.5 microns in size.

Particulate matter is made up of a wide range of materials and arises from a variety of sources, both natural and man made sources.

Particles can be primary (emitted directly into the atmosphere) or secondary (for example formed from other pollutants through chemical reactions that occur in the atmosphere and form mainly nitrates and sulphates.

Sources of primary PM include power stations, motor vehicles, cement factories, construction and quarrying.

Secondary PM is formed from emissions of ammonia, sulphur dioxide and oxides of nitrogen as well as from emissions of organic compounds from both combustion sources and vegetation.

Examples of naturally occurring particles are volcanoes and dust storms. The highest levels of PM10 are generally found in urban areas due to large amounts of vehicles.

 

 

 

 

Nitrogen dioxide (NO2) is a colourless, odourless gas which is produced as a primary and a secondary pollutant by combustion processes.

Emissions in the atmosphere are generally in the form of nitrogen oxides (NOx) which are a combination of nitric oxide (NO) and nitrogen dioxide.

Around 50% of the nitrogen dioxide present in the environment is from road vehicles. Nitrogen dioxide and volatile organic compounds increase the formation of low lying ozone, a chemical reaction initiated by sunlight.

Nitrogen dioxide is known to be highly toxic to various animals as well as to humans. High levels can be fatal, while lower levels affect the delicate structure of lung tissue. Humans exposed to high concentrations suffer lung irritation and potentially lung damage. Increased respiratory disease has been associated with lower level exposures.

Nitrogen dioxide is also a common indoor pollutant, being generated by gas cookers and heaters.

 

 

Ozone naturally occurs in the atmosphere and protects the earth from harmful radiation, but if ground level ozone is produced it can be detrimental to health. This type of ozone is formed through a complex chain of reactions.

Ozone, also known as smog, can irritate your respiratory system, causing coughing, irritation in your throat or a burning sensation in your airways. It can reduce lung function, so that you may have feelings of chest tightness, wheezing, or shortness of breath. Ozone can aggravate asthma and trigger asthma attacks. People at greater risk from ground-level ozone are people with lung diseases and children or adults who are active outdoors. 

 

This pollutant is created when a material containing sulphur is burnt. Much of the atmosphere sulphur dioxide comes from natural sources such as volcanoes. In the United Kingdom power stations are a major contributor to the levels of this pollutant in the atmosphere. Problem with sulphur dioxide pollution only occur where there are large numbers of households burning coal.

Sulphur dioxide is an irritant when it is inhaled and at concentrations over 1000ppb can cause severe problems in asthmatics such as narrowing of the airways. Asthmatics are considerably more sensitive to the effects of SO2 than other individuals and an effect on lung function may be experienced at levels as low as 200ppb. Other effects such as irritation of the eyes, nose, throat and lungs are often seen.

 

Hydrocarbons such as Benzene and 1,3 Butadiene are strongly linked to traffic emissions.  Exposure to both of the above mentioned pollutants over a long period of time have been linked with caner and leukaemia.  Benzene is a direct product of combustion and evaporation of petrol and is therefore highest next to roads and at petrol stations.

 

Carbon monoxide outside is produced in the same way as indoors, from the incomplete or inefficient combustion of fuel.  This includes the use of cars that are ‘cold’ or have poorly tuned engines.  Although average levels of carbon monoxide in the UK have decreased over the years, the concentrations next to major roads can often be quite high.  The health effects of outdoor carbon monoxide are similar to those produced indoors but the concentrations are not high enough to be fatal.

 

Lead pollution is generally caused by vehicle emissions and other industrial processes such as paint manufacture.  Concentrations of lead are much lower nowadays due to the replacement of leaded petrol with unleaded.

 

Lead poisoning can effect the intellectual development of children, and at very high doses poisoning, brain and organ damage can occur.