ENVIRONMENTAL SCIENCE PUBLISHED FOR EVERYBODY ROUND THE EARTH
Cities became an important part of our environment in the 19th Century and they expanded rapidly in size in the 20thCentury. Many natural factors control the climate in urban areas, for example, the latitude, whether the city is in a mountain region or on a flat plain, whether it's close to the sea and what the surrounding land is used for. The presence of a large number of buildings in a relatively small urban area also changes the local climate.
The presence of buildings changes the air temperature and wind speed and direction in the city. Human activity, particularly industry and transport, also affects urban climate through emission of large amounts of air pollutants. Air pollution has a negative impact on the natural environment, on the economy and on our health. Air pollution problems include acid rain and smog episodes. There are many regions of the world which suffer from air pollution problems, for example the so-called "Black Triangle" which is located between Poland, Germany and The Czech Republic.
Air pollution is a serious problem in cities. It changes our urban climate, degrades the environment and has negative impacts on the economy and on our health. Industry and transport are the largest sources of air pollutants and emission of these pollutants results in high levels of particles and soot in the air and can cause smog to form.
Industrial accidents can cause huge inputs of air pollutants into the atmosphere and these emissions may lead to permanent degradation of the natural environment. One of the most polluted regions in Europe is the so called "Black Triangle", located at the junction of the borders of Germany, Poland and The Czech Republic, where huge brown coal resources are exploited.
As the atmosphere is constantly moving, pollutants are carried great distances away from their source region. This means that air pollution is an international rather than local problem.
Many natural factors control the climate in urban areas, for example, the latitude, whether the city is in a mountain region or on a flat plain, whether it's close to the sea and what the surrounding land is used for. As a city grows, new factors (e.g. heat from human activities and air pollution) modify the local climate and contribute to the formation of distinct urban climates.
Large numbers of people and heat from human activities, along with the fact that cities are built mainly of concrete, asphalt, bricks and stones, makes the temperature in a city higher than in a non-urban area. High density building alters the wind speed and its direction and a local air circulation, called the urban breeze, developes.
Water is essential for life on Earth and its quality is, therefore, of great importance. Clean rain is naturally slightly acidic but when the pH of rain falls below 5.6, we call it acid rain. Emissions of the two air pollutants, nitrogen oxides (NOx) and sulphur dioxide (SO2) are the main reasons for acid rain formation. Emissions of these pollutants are decreasing in Europe and North America but are still increasing in Asia.
Acid rain affects the whole environment. Polluted rain enters surface waters and permeates into the groundwater. It makes the aluminium in the soil reactive and leaches out the nutrients. Trees and plants are damaged both through the decrease in soil nutrients and also directly by the acidic rain falling on them. Biodiversity in areas affected by acid rain is likely to be poor.
Areas affected by acid rain are found mainly in Europe, the United States of America and in China. Affected regions are generally close to highly urbanised and industrialised areas but long range transport of air pollutants can result in acid rain damage far away from the pollution sources.