7.5.2 Air pollution
Air pollution can exist at all scales, from local to global, and can include gases and solid particles. It can affect you in your own home, or in your town or city, and can contribute to global atmospheric changes. The most common sources of air pollution in the urban centres of Ethiopia include the burning of wood, charcoal and other biomass fuel by households, small businesses such as bakeries, manufacturing industries, and vehicles.
Air pollution is defined as the presence in the air of abnormal amounts of chemical constituents capable of causing harm to living organisms. Clean air consists of nitrogen (78% by volume), oxygen (21%) and trace gases (< 1%). Polluted air may contain particulate matter (such as black soot) and many different gaseous chemicals such as carbon monoxide, carbon dioxide, nitrogen oxides, sulphur oxides, ozone, nitrates, sulphates, organic hydrocarbons and many others. Many of these are also found in clean air as trace gases but they become pollutants if present in abnormal quantities.
The emission of black smoke is an indication of intense pollution. However, not all air pollution is visible or can be smelled. Gases such as carbon monoxide and carbon dioxide are invisible and odourless. Carbon monoxide is very dangerous to humans. It can be produced by inefficient burning of fuel (for example a charcoal stove in a home with inadequate air supply) and if breathed in large quantities it can be deadly. Carbon dioxide is an important pollutant that is involved in climate change. (You will learn about in climate change in Study Sessions 9, 10 and 11.)