Ozone in the Environment

By: Diana Gonzalez

Ozone and its Chemical Processes


Ozone is composed of two different forms of Oxygen: O2 and O3

O2 (g) -------> O (g) + O (g)

O (g) + O2 (g) ----------> O3

In the equations above, UV radiation breaks down an oxygen molecule into 2 oxygen atoms. The two oxygen atoms then bind to other oxygen atoms to form other ozone molecules.


Ozone can also be depleted through anthropogenic sources such as Nitrogen Oxides and Chlorofluorocarbons. These act like catalysts that decompose ozone to oxygen.

Nitrogen Oxides

NO (g) + O3 (g) ----> NO2 (g) + O2 (g)

NO2 (g) + O (g) ------> NO (g) + O2 (g)

In the equations above, nitrogen oxides bind together with either O3 or O to form O2 and either NO2 or NO.


CCL2F2 (g) ------> CClF2 (g) + Cl (g)

Cl (g) + O3 (g) ----> O2 (g) + ClO (g)

ClO (g) + O (g) ----> O2 (g) + Cl (g)

O3 (g) + O (g) ------> 2O2 (g)

Both NO and CFC's are harmful to the ozone because they can create a hole in the ozone layer in the stratosphere which in turn will let direct UV rays hit the Earth.

Natural Processes

Traces of ozone occur in very small amounts in our stratosphere. Ozone reaches its maximum amount at about 120 km above earth's surface. It is formed mostly from trioxygen (O3) and contains some oxygen gas (O2). Oxygen's main purpose is to protect earth from harmful radiation from the sun. It is estimated that ozone absorbs all radiation that lies in the UV-B region, which is about a 280-315 nm wavelength.

As stated before, oxygen is made up of O3. When sun shines, it emits ultra violet light. This light causes O2 molecules to split up into single O atoms in a process called photolysis, the decomposition or separation of molecules by light. These individual O atoms then react with other O2 molecules to form O3, or in other words, ozone. Thus ultra violet light can make and split ozone molecules.

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Anthropogenic Processes

We know that ozone is existent in our stratosphere (6 – 30 miles above our earth) but ozone also creates a layer in the troposphere The troposphere is the area below the stratosphere closer to our ground. However, unlike stratosphere ozone which protects us, troposphere ozone serves as an air pollutant. "Bad" ozone is created because it reacts with oxides of nitrogen and volatile organic compounds (VOC) in the presence of sunlight. You may be thinking that we can't do anything about this, but in reality us humans have great responsibility when it comes to ozone turning into a pollutant.

A great majority of human activity contributes to ozone turning into pollution. The VOCs and oxides of nitrogen that react with ozone come from industrial factories, motor vehicles, and electric utilities that we humans use. Motor vehicles produce 56% of all NOx and 45% of all VOCs alone. Industrial facilities produce another 22% of all the NOx and 50% of all VOCs. These harmful reactors are known as ozone precursors. Another anthropogenic effect that results from human activity is ozone depletion. Ozone can be decomposed by nitrogen oxides and CFCs.

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