The pollutants present in the air of our cities are as diverse in their variants as the problems they cause. Below is a list of the more common air pollutants, with a definition, the problems they cause and links to other resources on the pollutant.

PM 10

PM 10s are Particulate Matter, or particles which have a diametre of 10 microns or less, that's 25 times thinner than a human hair or smaller. PM 10 is made up of many different pollutants, primary, soot, dust, brake dust, pollens, mold spores, heavy metals and hydrocarbons for example, and secondary, such as combinations of NOx, NH3, SO2 and VOCs, solid and liquid.

The main contributors of PM 10s are traffic, agriculture and industry.

Effects: PM 10s affect the respiratory tract causing coughing and wheezing and shortness of breath, and the cardiovascular system, increasing the risk of heart disease. Irritates the mucose membranes, worsens bronchitis and asthma and increases the risk of cancer. The heavy metals can reach humans through the alimentary chain once they precipitate to the ground.

More information on PM 10s can be found here, here or ici (fr)

PM 2.5

PM 2.5 is Particulate Matter which has a diametre of 2.5 microns or less (100 times smaller than a human hair or less). PM 2.5s are made up of the same components as PM 10s but smaller. Being smaller they travel further and have more serious effects on health.

The main contributors of PM 2.5 are traffic, fires (burning rubbish, buildings or vegetation) and smelting metal.

Effects: Because PM 2.5s are so small they can penetrate deeply into the lungs. This has the same effect as PM 10s but with increased risk of cancer, emphysema, heart disease, reduced lung capacity and damage (tissue scarring) and high risk of premature death in people with existing heart or lung disease.

More information on PM 2.5s can be found here or here

CO2

Carbon dioxide, the most famous of greenhouse gases, is a colourless and odourless gas which is heavier than air and so stays low to the ground.

The main contributor in cities is traffic.

Effects: Breathing an atmosphere with concentrated levels of CO2 will cause loss of consciousness followed by death. Long term exposure to high levels can cause headaches and lack of concentration. CO2 is one of the principle greenhouse gases.

CO

Carbon monoxide is formed when a fuel is burnt without a sufficient air supply. It is a colourless and odourless gas.

The main contributor of CO in cities is traffic from incomplete combustion

Effects: Carbon monoxide is poisonous to all living, breathing creatures. When inhaled it binds to the haemoglobin in the blood instead of oxygen, which reduces the blood's oxygen carrying capacity. An exposure of 200 ppm for a few hours is required by most healthy people before they feel the effects, but prolonged exposure or more concentrated exposure can lead to death. CO is also an Ozone precursor.

More information on CO can be found here

NOx

The oxides of nitrogen NO and NO2 are put together because NO oxidises very quickly in the atmosphere into NO2. NO is colourless but NO2 has a rust colour in high concentrations.

The main contributor of NOx is traffic.

Effects: These oxides affect the respiratory tracts exacerbating conditions like asthma and bronchitis and damage plants. It can cause over fertilisation of plantlife in high concentrations. NO2 is a main precursor of acid rain formation. Combined with water it forms a weak solution if nitric acid. It also combines with other pollutants, such as ozone to form secondary pollutants. Accumulation on buildings erodes the brick and concrete.

More information on NOx can be found here or ici (fr)

SO2

Sulphur dioxide results from the combustion of fuels containig sulphur. It is colourless with an acrid smell in high concentrations.

The main contributors are traffic, coal power plants, industrial and home heating.

Effects: SO2 affects the respiratory tracts, is a component of urban smog and summer haze and damages plants. It is also the second main precursor of acid rain. Forming a weak solution of sulphuric acid. Accumulation on buildings erodes the brick and concrete.

O3

Ozone is good when it is in the stratosphere (the upper part of the atmosphere), protecting the Earth from harmful UV radiation but it is a secondary pollutant when it forms in the troposphere (the lowest part of the atmosphere) under the effect of sunlight. It forms from oxides of nitrogen, NOx, and volatile organic compounds, VOC, present in the air.

The main contributor of the precursor pollutants are traffic and industry.

Effects: Ozone is the main ingredient of urban smog and summer haze, especially bad in summer because of all the sunlight. When breathed in high concentrations it irritates the mucose membranes in the respiratory tracts, causes coughing, chest pain, throat irritation, congestion, inflamation of the lining of the lungs and worsen bronchitis and asthma. Ozone is responsible for up to 20'000 deaths a year in Europe alone. Low level Ozone also damages vegetation, reducing crop and forestry yeilds and acts as a greenhouse gas.

More information on Ozone can be found here, here and ici (fr)

Lead

Lead is a heavy metal found in some petrol and old paint and used in anticorrosion treatments.

The main contributors to atmospheric lead are traffic and burning rubbish.

Effects: Lead accumulates in the bodies organs and bones. It causes mental retardation in children, reduced mental abilities, nerve damage, organ damage such as liver and kidneys, may interfere with blood formation and cause high blood pressure and cardiovascular disease.

Benzene

 Benzene is a colourless liquid with a characteristic odour. It is found in petrol and gets into the air from combustion or evaporation.

The main contributors of atmospheric benzene are traffic, heating and the stocking, transportation and transference of petroleum products.

Effects: Benzene is amongst the pollutants which are cercinogenic. There is no 'safe' exposure level to benzene. In high concentrations benzene affects the respiratory tracts, the eyes and the central nervous system and does serious damage to plants.

 VOC

Volatile Organic Compounds are formed from the evaporation of solvents or carburants and from incomplete combustion. They are a mix of a variety of chemicals both toxic and non toxic.

The main contributors are traffic and industry, but VOCs are found in paints, coatings, underarm deoderants and cleaning fluids to name a few.

Effects: The effects will vary depending on the chemicals in the compound, from mild irritation to the risk of cancer in the case of benzene. VOCs are a majour precursor to ozone formation causing urban smog and summer haze.