Ozone Layer Depletion

Ozone layer depletion refers to the decline in amount of ozone in Earth's stratosphere (commonly known as Ozone layer) and a large springtime decrease in stratospheric Ozone around the Antarctic region.

Stratospheric ozone is highly beneficial as it protects the living organisms on the Earth's surface from harmful UV radiations of the sun. Ozone is continuously formed and removed in the stratosphere and thus there is an apparent equilibrium in the ozone layer with the concentration of ozone remaining constant.

However satellite data indicated a large hole in the ozone layer over Antarctica. The main process which was responsible was found to be catalytic destruction of ozone by atomic halogens. The main source of these atomic halogens are Chlorofluorocarbons (CFC), Hydrochlorofluorocarbons (HCFC) and Chlorofluorobromine. These gases are used as refrigerants, solvents, propellants and foam-blowing agents. They are very stable and are inert in lower atmospheric regions but get destroyed when exposed to UV rays resulting in release of atomic halogens. This destruction of ozone layer by atomic halogen takes place through the following processes as outlined below.

CF₂Cl₂ + UV Radiations → CF₂Cl + Cl

This free chlorine atom then acts as a catalyst for the following reactions.

Cl + O₃ → ClO + O₂
ClO + O → Cl + O₂
O₃ + O → 2O₂

The chlorine is thus free to repeat after this two-step cycle. On an average, a single chlorine atom is able to react with 100,000 ozone molecules before it is removed from the catalytic cycle. This fact plus the amount of chlorine released into the atmosphere yearly by chlorofluorocarbons (CFCs) and hydrochlorofluorocarbons (HCFCs) demonstrate how dangerous CFCs and HCFCs are to the environment.

Global Warming

Global warming is the increase of Earth's average surface temperature due to the effect of greenhouse gases like carbon dioxide which is produced due to burning of fossil fuels or from deforestation. These greenhouse gases trap the heat radiated from the Earth's surface and thus increase the temperature. This phenomenon is known as greenhouse effect.

Greenhouse gases such as water vapor, carbon dioxide, methane, nitrous oxide, ozone and chlorofluorocarbons (CFC) absorb most part of radiations from Earth's surface. The atmosphere is, thus, heated and then some energy is radiated back to Earth while some of it goes to space. If there were no greenhouse gases, all the energy would have been radiated to the space and the our planet would have been very cold. Hence greenhouse gases are essential for maintaining the Earth's temperature at the present conditions. However increase in concentration of greenhouse gases beyond acceptable limit will increase absorption of radiations and increase the Earth's surface temperature.

Effects of Global Warming

- Melting of ice caps and glaciers
- Rising sea levels

- Changes in rainfall patterns
- Widespread decrease of flora and fauna
- Spread of diseases like malaria, dengue etc.
- Loss of plankton due to warming seas

Sources of Pollution

An air pollutant is a substance in the air that can have adverse effects on human beings and other living things. The substance may be solid particles, liquid droplets or gases. It can be of natural origin or man-made.

The air pollutants are classified into two main types:

1. Primary Pollutants

2. Secondary Pollutants

1. Primary Pollutants

These substances are emitted directly into the atmosphere. Carbon oxides, sulfur oxides and nitrogen oxides emitted by automobiles are examples of primary pollutants.

2. Secondary Pollutants

These substances are not emitted directly into the atmosphere, but are formed by various physical processes in the atmosphere. Ground level ozone and peroxyacetyl nitrate (PAN) are examples of secondary pollutants.

Air Pollution: Introduction

Air pollution is the introduction of harmful substances at an undesirable concentration into the Earth's atmosphere which make the air unsafe for living.

Air is precious and is essential for sustaining life on the planet. It provides oxygen required for respiration, carbon dioxide for photosynthesis, and nitrogen for synthesis of amino acids and proteins. The ozone layer in stratosphere absorbs harmful UV rays, thus protecting the living organisms from harmful effects of these radiations.

Any change in composition and quality of air caused by introduction of harmful substances can affect life on Earth severely. The main sources of air pollution are automobile emissions, burning of fossil fuels and industrial processes. Naturally occurring processes like volcanoes, dust storms, forest and grassland fires also cause air pollution.