Ozone depletion: Thinning of the stratospheric ozone layer is known as ozone depletion. Such depletion causes the 'ozone hole', resulting in poor screening of the harmful UV rays and increase in incidences of skin cancer. Some of the common agents that deplete ozone are CFCs.

Peroxyacetyl nitrate (PAN) is a secondary pollutant present in photochemical smog. It is thermally unstable and decomposes into peroxyethanol radicals and nitrogen dioxide gas causing eye irritation

Particulate matters are tiny particles of solid matter suspended in a gas or liquid. Combustion of fossil fuels, fly ash produced in thermal power plants, forest fires, asbestos mining units and cement factories are the main sources of particulate matter pollution.

Air pollutants can be
(i) discharge of dusts or particulate matter (PM: 2.5 and 10)
(ii) discharge of gases (SO_x, NO_x, CO and CO₂)

The alterations or changes in the composition of the Earth's atmosphere by natural or human activities (anthropogenic factors) are referred as Air Pollution.

Pollution is any undesirable change in the physical, chemical and biological characteristics of the environment due to natural causes and human activities.

Sources of water pollution can also be classified in three ways. They are municipal wastes, industrial wastes and agricultural wastes.

Ozone is found in the layer of the atmosphere called stratosphere. It acts as a protective covering that absorbs ultraviolet radiation from the sun. It is found about 15 and 50 kilometers from the ground level.

(i) 1992: Earth summit, Rio de Janeiro. Agenda 21, otherwise called Rio conference, Brazil
(ii) 1997: Kyoto Protocol, Japan.

4 'R' refers to refuse, reduce, reuse and recycle. It is the best available remedy for plastic waste pollution.

Air Quality Index (AQI) is a number used by government agencies to communicate to the public how polluted the air is at a given time.

The alteration or changes in the composition of the earth's atmosphere by natural or human activities (anthropogenic factors) are referred as air pollution.

Pollutants are classified into:
Non degradable and degradable pollutants. Degradable pollutants are further classified as rapidly degradable and slowly degradable.

The naturally occurring greenhouse gases in the air, mainly carbon dioxide, methane and water vapour trap radiation from the sun and act like a thermal blanket around our planet earth. Without the greenhouse gases, the earth would have an average temperature of -180 c and be covered in ice. The greenhouse effect keeps the earth warm enough to sustain life.

Green House Effect and Global warming:
Natural environment and climate are dynamic and keep changing over course of time. Reasons for climate change
a) Human population growth
b) Industrialization
c) Associated anthropological activities the changes.
Impact on Global Warming:
(i) Large-scale changes of global environment can lead to hazards, which may include climate change, stratospheric ozone depletion, changes in ecosystems due to loss of biodiversity, changes in hydrological systems and the supplies of freshwater, land degradation, urbanization, and stress on food-producing systems.
(ii) Greenhouse gases (GHG) water vapour, carbon dioxide, methane, nitrous oxide, ozone and some artificial chemicals such as chlorofluorocarbons (CFCs) causes greenhouse effect. The absorbed energy warms the atmosphere and the surface of the Earth
(iii) Global warming will have a significant impact on people and nature. As global average temperatures rise, precipitation patterns could be affected. Extreme wet and dry conditions can be expected (flooding and desertification). Coastal areas shall become more vulnerable to storm surges as sea level rises. Plant and animal species will migrate or disappear in response to climate change.
(iv) Global warming can directly affect the flora and fauna. This could also result in shortage of food and even lead to a food crisis and affect the health of the people and organisms.
Control Measures:
The UNO has several measures to control or reduce pollution. Through various conventions organized by UNO, the countries assured to take steps to control or reduce emissions by factories and automobiles.