Subjects related to air pollution or air quality are not recent subjects. The first determination of complaints regarding the subject emerged so long ago in medieval times, starting with use of coal for heating in Europe. From second half of the 19th century, main Europe cities' atmosphere was regularly polluted due to coal smoke in winter season, this caused increasing mixing of fog and smoke called smoky fog. During past periods, pollution originated from houses and factories were worse compared to now, because there were limited laws which control mixture of the pollution to the air.  

Air pollution is a phrase used to identify any hazardous materials in the air we breathe. Air pollutants are coming from natural resources like deserts or volcanoes and one of the main reasons of pollution in internal and free atmosphere is human. Air pollution will cause poor air quality, and will create various effects on human as well as on environment.

The most important sources of the air pollution are vehicles, factories, powerhouses and domestic heating. Number of vehicles on the road is increasing. Every vehicle burns fuel, generally hazardous chemical mixtures included in the smoke spreads to the external environment from exhausts and in conclusion it pollutes the air. We all bargain on electricity usage to make comfortable our daily life as cooking, watching TV. Electricity power is obtained as a result of burning the fossil fuels in the plants. As the fuel is burned, sulphur dioxide and nitrogen oxide are released to the atmosphere via chimneys. Dust is generated as a result of many human activities, and these particles are called particulate material.

Main features of major (free environment) air pollutants will be explained below in detail.

Nitrogen Dioxide (NO2): Nitrogen oxides will be formed whenever something burns in the air.     This is because, the air we breathe basically consists of Nitrogen (78%) and Oxygen (%21) and these are combined when there is energy (burning materials) in the environment.

Most common nitrogen oxides are (generally identified as Nox) nitrogen Oxide (NO) and Nitrogen Dioxide (NO2).  Nitrogen oxide (NO) is a odourless and colourless gas, is gained with burning the fuel inside at high temperature; for example, cars and other road vehicles, heaters and cooking appliances. They immediately combine with oxygen when they are airborne and form nitrogen dioxide (NO2). Although some of them released from the sources directly, bulk of nitrogen dioxide found in the atmosphere emerges as a result of oxidation of nitrogen oxide's. Same conditions applies too tobacco smoke too.

This is a red brown and non-combustible gas and has a distinctive smell. It is poisonous in important concentrations and in conclusion lung injuries may emerge which has serious delayed affects. Other health affects of exposure to the nitrogen gas are being out of breath and chest pains. Nitrogen dioxide is a strong oxidation agent, it forms corrosive nitric acid by reacting with air and water vapour, and also forms toxic organic nitrites. Thus, it leads to acid rains which cause detrimental effects to trees, fishes and animal life. Also NO2 has a main role in atmospherical reactions which provide ground level ozone and smoky fog.

Nitrogen dioxide is a traffic-concerned pollutant, and its concentrations are high in urban areas compared to rural areas.

Particulate Materials (PM10 and PM2.5) : Particles are defined according to their aerodynamic diameters; for example, PM10 (particles which their aerodynamic diameters are less than 10 µm) or PM2.5 (particles which their aerodynamic diameters are less than 2,5 µm) Main components of PM are sulphates, nitrites, sodium chloride, mineral salts and water. Material is a complex mixture of solid and liquid particles of organic and inorganic materials suspended in the air.

PM10 generally includes soil crusty materials, road vehicles and industrial plant dusts. PM2.5 constitutes of secondariy formed aerosols, combustion particles and again condensed organic and metalic vapours. Acid components of particle materials are formed as thin particles.

A further decomposition will be primary or secondary classification from particles' origins. Primary particles spread to the atmosphere directly whilst the secondary particles consist of as a result of other pollutants reactions. Secondary particles formed in rural environment are generally sulphates and nitrites constituted as a result of concentrations including sulphur dioxide and nitrogen oxides.

Tropospheric (at the bottom layers of the atmosphere) Ozone (O3): Ozone (O3) is a triatomic form of molecular oxygen. Material is a toxic, pale blue and nonstable gas, and has a strong odour. Ozone is especially in stratosphere and stands as a natural layer 19 -30 km above from earth surface. At the mentioned elevations, ozone filters ultraviolet (UV) radiation which goes to the ground surface. Ozone at the level of ground surface threatens human health seriously. Ozone is a strong oxidant.
Trosphorefic Ozone’s lifetime in the atmosphere is 22 days.

Benzene and other VOCs: Volatile Organic Compouns or VOC are organic chemicals which can evaporate easily at room temperature. These are defined as organic because they have carbon elements in their molecular structures. VOCs include very wide range compounds such as hydrocarbons (for example, benzebe and toluene), halocarbons and oxygenates.

Hydrocarbon VOCs are generally classifed as methane and non-methane other VOCs. Methane is an important component of VOCs, directly contributes global warming and ozone formation at ground level or at low levels of atmosphere. A major part of methane released to the atmosphere is escape natural gas which escapes from natural gas distribution systems via leakage path. Benzene is a non-methane hydrocarbon, and colourless and clear liquid. This material is very stable but is volatile in a high level and ready to evaporate at room temperature.

Sulphur dioxide (SO2): SO2 is colourless and noncombustible gas and it has a strong odour. This gas is generated as a result of burning the fossil fuels (coal and fuel oil) and disposal of ore minerals including sulphur. H2SO4 is formed as a result of further oxidation of SO2 and generally to have a catalyst similar to NO2 benzene and in conclusion acid rains are constituted. Also, sulphur dioxide emissions pioneer for particles in the atmosphere.

Carbon Monoxide (CO): Carbon monoxide (CO) is a colourless, odourless and tasteless gas and is a bit lighter than air. Gas is toxic in a high rate for human and animal when they are much, also they are produced in a low rate in normal animal metabolisms and it’s believed that it has some normal biological functions. Carbon monoxide (CO) is produced when fuels including carbon and there is low amount of oxygen. Also, it is produced when the fuels are burned at very high temperatures. Gas burns as a blue flame in air or oxygen.
In environment which there is enough O2 supply, a major part of carbon monoxide which consist during burning will convert to Carbon dioxide (CO2) via oxidation.

Carbon Dioxide (CO2):  Carbon dioxide, below standard temperature and pressure, stands as gas in the atmosphere. Carbon dioxide is colourless. It’s odourless at low concentrations. It has a strong acidic odour at high concentrations.
CO2 is a trace gas and covers 0.039% of the atmosphere. It is released out during respiration of animals fed by plants directly or indirectly, by fungi and microorganisms. Thus, it is the main element of carbon cycle.

Lead: Lead is a soft and moldable metal, its symbol is Pb. Lead exists as very small particles in the air. It belongs to the family of heavy metals. Metallic lead has a blue-white colour, but it becomes dull and turns a faint grey colour when it is in the form of gas.
Aerosolization of the lead is occured as a result of soil erosion, volcanic eruptions, sea sprays and scrub fires. Natural concentration of the lead in the air is less than 0.1 microgram per each cubic meter.