Ozone

Ozone is a gas composed of three atoms of oxygen. It is less stable than o2. Ozone occurs both in the Earth's upper atmosphere (stratosphere)and at ground level(trophosphere). Ozone can be good or bad, depending on where it is found: Gaseous ozone is bluish in colour and has a pungent distinctive smell. The name of ozone is derived from the greek word “ozein “ meaning “To smell”. The smell of ozone can often be experienced near electrical transformers or nearby lightening strikes. It is formed in these instances, when an electrical discharge breaks Standard way to express total ozone in atmosphere is by Dobson units. Average concentration at a point is meassured in Parts per bilion .(ppb) or ug/m3.

 

Most people can detect about 0.01ppm of ozone in air with its specific sharp odour Exposure of 0.1-1ppm produce headache, burning eyes, irritation to respiratory passages.
The ozone reacts in three ways:
1. Direct oxidation on the substrate by the process of ozonolysis;
2. Direct oxidation on a substrate for the oxygen atom loss;
3. Catalytic oxidation due to the oxygen present in ozonized air.


Ozone in Stratosphere

Stratospheric ozone occurs in the upper atmosphere and is often called “good ozone.” which is mostly produced from UV-rays reacting with O2. It forms a protective layer, which filters photons of shorter wavelength from Uv-rays of sun. Ozone in the stratosphere protects the Earth’s surface from harmful ultraviolet radiation. Currently, the stratospheric ozone layer is being depleted by chlorofluorocarbons (CFCs) and other ozone-depleting substances. The stratospheric ozone layer is thinning slightly globally but is most notably thinning over the polar regions. The ozone hole in the Antarctic is a region of substantial ozone thinning

 

Ozone in Troposhere

Tropospheric ozone is O3 gas that is found near the Earth’s surface. It is often referred to as “bad ozone” because levels are increasing due to human activity and because it cause detrimental health and environmental effects. It is irritant to mucous membranes of eyes and lungs and also burns sensitive plants. ozone (also called ground level ozone or surface ozone) is an air pollutant and a greenhouse gas that occurs near the surface of the Earth. Ozone near the surface of the Earth is a minor greenhouse gas that contributes to about 7% of the total warming. Natural sources of tropospheric ozone include lighting during thunderstorms and downward mixing of O3 from the upper layers of the atmosphere. Anthropogenic derived ozone is formed through photochemical reactions that are driven by sunlight. Ozone is not emitted directly from a tailpipe or a smokestack; rather it is formed through reactions with volatile organic compounds (VOC) and oxides of nitrogen (NOx). Sunlight plays a very important role in the formation of ozone. Therefore there are large diurnal and seasonal changes in the concentrations of O3 in the lower atmosphere.Typical summertime maximum levels of stratospheric ozone range from 100 to 400 ppb of O3 in urban and suburban areas. Levels in rural areas range from 50 to 120 ppb. Remote tropical forests and marine areas have ozone concentrations of 20 to 40 ppb. Due to natural sources of ozone, background concentrations range from 20 to 30 ppb globally .

 
 

Ozone Types and Uses