# Atmospheric Pollutants

Atmosphere surrounds the earth’s surface, it is of different thickness at different heights. There are five layers of atmosphere with each layer having a different density. Troposphere is the lowest layer of the atmosphere where all organisms live. It extends roughly up to 10 km in height above the mean sea level. This layer contains air, water vapour and clouds. Stratosphere is the next layer which extends from 10 km to 50 km in height. It contains dinitrogen, dioxygen and ozone layer. The ozone layer protects the humans and other animals from the harmful ultraviolet rays of the sun. Atmospheric pollution caused by atmospheric pollutants is actually referred to as the pollution of troposphere and stratosphere.

The presence of undesirable solids or gaseous components in air causes tropospheric pollution. The pollutants can be classified as:

• 1) Gaseous pollutants – Oxides of sulphur and nitrogen, hydrocarbons, ozone and other oxidants fall under this category. Let us have a deeper look at each pollutant:

• a . Oxides of sulphur – When fossil fuel is burnt, oxides of sulphur are produced. Sulphur dioxide is poisonous in nature. Studies show that very low concentration of sulphur dioxide causes respiratory diseases. In presence of particulate matter sulphur dioxide is oxidized to sulphur trioxide.

$~~~~~~~~~~~~~~~$ 2SO2 (g) + O2 (g) →  2SO3 (g)

• b. Hydrocarbons – They are formed by incomplete combustion of fuels. They are carcinogenic that is they cause cancer. They are very harmful to plants as they cause ageing, break down of tissues and shedding of leaves.

• 2) Particulate matter – Minute solid particles or liquid droplets suspended in air are called particulate matter. There are two types of particulates namely, viable and non-viable. Minute living organisms such as bacteria and fungi, which are dispersed in the atmosphere are known as viable particulates. Non-viable particulates are classified according to the size and nature of the particulates. For example, smoke consists of solid and liquid particles which are formed during the combustion of organic matter. On the other hand, dust is composed of fine particles which are produced during grinding or crushing.

Moving on to the stratospheric pollution, the stratosphere consists of ozone layer which saves the earth from harmful ultraviolet rays. The ultraviolet radiations splits the dioxygen molecule into free oxygen atom, now these free oxygen atom combines with the dioxygen molecule to from ozone.

$~~~~~~~~~~~~~~~~~~~~$ O2$\require{AMScd} \begin{CD} @>uv>> \end{CD}$  O (g) + O (g)

$~~~~~~~~~~~~~~~~~~~~$ O (g) + O2 (g)  ⇌ O3(g)

Ozone is unstable and breaks down to oxygen molecule. Chlorofluorocarbons are the main reason of ozone depletion, they react with ozone to form chlorine monoxide radical and oxygen molecule. CFC’s are the agents which are producing chlorine radicals in the stratosphere and damaging the ozone layer. This damage to ozone layer is a threat to the survival of organisms as ozone protects the earth from harmful rays of the sun which can cause skin cancer.

We have seen the different types of pollutants in the atmosphere and the various reactions that occur in its layers. For any query on these topics call our mentor support team at Byju’s.’

#### Practise This Question

Recently discovered micro organisms capable of metabolising chlorinated hydrocarbons possess