Smog
Smog is a combination of the words smoke and fog. We can distinguish two separate types of smog, summer smog and winter smog.
Photochemical smog, or summer smog, mainly consists of ozone. It is a brown, oxidising fog. The causes of photochemical smog are nitrogen oxides and VOC, which stem from traffic and industries. Ozone is formed according to the following chemical reactions:
NO2 + uv --> NO + O
O + O2 --> O3
The reverse reaction is:
NO + O3 --> NO2 + O2
The best circumstances for the creation of high ozone concentrations are summer temperatures, direct sunlight and standing air layer, which enable dilution of contaminants.
Humans cannot adapt to smog. Health effects of smog greatly depend upon the concentrations of ozone and other photochemical oxidants. These contaminants cause eye and respiratory irritations. Plants are extremely vulnerable to ozone. Even in low concentrations it can cause serious damage.
Winter smog is also referred to as acid smog; it mainly consists of foggy elements. Winter smog is found in areas where vertical dispersion of air pollutants is not possible. Usually temperatures decrease during the day in high air layers.
Heated air layers near the earths' surface rise, causing the air pollutants to be dispersed vertically, and to be diluted. In winter ground temperatures are sometimes lower than those of the upper atmospheric layers, causing the air to stay near the ground, so that pollutants will not spread. This causes winter smog.
Winter smog can form when temperatures are low and sulphur dioxide concentrations increase consequential to central heater emissions from houses.
The cold outside air will cause moist to condensate into fog. Aerosols in air play a part in this process, because they serve as condensation cores for water vapour.
Humidity aids the transfer of sulphur dioxide to sulphuric acid, causing the smog to be acid. Acid smog causes breathing problems and eye irritations.
