SMOG In the period of silence or at low speed of the wind, smoke ( fumes) from power plants, waste incinerators, and industrial chimneys rise, more or less vertically, up into the air. That is why harmful substances spread over large areas and their concentration is relatively low. However, who observes this phenomenon closely, is able to notice that there are days when first the smoke goes up but then it does not move but rather settles down in form of a whirled layer, parallel to the surface of the ground. How can we explain this phenomenon? In normal conditions, the temperature of the troposphere decreases with the increasing altitude. Unfavorable weather conditions can cause that the cold layer of air is covered with a lighter and warmer layer of air what disrupts the process of rising the lighter air from the Earth's surface. Smog occurs because of the stratified movements of the air and large amounts of harmful substances which are emitted into the air.

Depending on the conditions in which the smog occurs, we differentiate two types of Smog: The London Smog and The Los Angeles Smog.

The London Smog occurs with the inversion of temperature, especially in the months from November to January, in moderate climate zones. The main components of The London smog are sulphur dioxide and its derivative products, elementary entities of soot, as well as carbon oxide. However, sulphur dioxide is the main component of the harmful substances. A disastrous number of this type of smog has multiplied in the recent years, not only in London but also in other big cities like: New York, Tokyo, Berlin, Hamburg, Hanover.

The Los Angeles smog occurs mainly in the summer months, in the subtropical zone. In this type of smog, the most harmful substances are the following: nitrogen oxide, hydrocarbon, carbon oxide and ozone. The last one occurs with strong sun radiation as a result of some chemical reactions and is believed to be the most harmful ingredient. A large part of The USA, which is in the subtropical region, has favorable conditions for this type of Smog as it has enough radiation, much more then industrialized areas of the moderate zone.

If we want to limit the occurrence of Smog, we should:

- limit the emission of fumes from the chimneys of our factories
- limit the use of our cars and rather choose public transport
- express our opinions loudly about what we think is bad
- do everything the best for our environment so that we can all live a better life.