Page 214 - Chemistry ICSE Class IX

202 ICSE Chemistry – 9

Let us say it Again

— Environment. The physical and biological world around us is called environment.
— Environmental pollution. The contamination of the environment with harmful toxic, poisonous substances due to
certain natural phenomenon and human activities is called environmental pollution.
— Types of environmental pollution. Environmental pollution can be categorised in the following types:
 Atmospheric pollution (or Air pollution)
 Water pollution
 Soil pollution (or land pollution)
 Thermal pollution
 Noise pollution
 Radiation pollution
— Atmosphere. The cover of the air surrounding the earth is called atmosphere.
— Atmospheric pollution. Contamination of the atmospheric air with harmful toxic gases, smoke and particulate matter,
e.g. dust, etc., is called atmospheric pollution.
— Air pollution. Contamination of the air around us (in the troposphere) by harmful toxic gases, smoke and particulate
matter, beyond certain permissible level is called air pollution.
 Air pollutants are of two types: Gaseous pollutants and particulates.
— Smog. The smoke + fog conditions are called smog. There are two types of smog.
 Chemical smog
 Photochemical smog
— Acid rain. All forms of precipitation, such as rain, snowfall, fog, and dew, which are more acidic than normal water are
called acid rain.
 Acid rain is caused by the dissolution of oxides of sulphur and nitrogen in atmospheric moisture or rain.
 Acid rain damages structures made of iron and marble (or lime). It is harmful for vegetation, aquatic life.
— Global warming. The gradual increase in the global temperature (or temperature of the earth) caused by the increased
concentration of the greenhouse gases in the atmosphere is called global warming.
— Greenhouse gases. Carbon dioxide (CO ), Methane (CH ), Nitrous oxide (N O), Ozone (O ), Water vapour (H O) and
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2
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Chlorofluorocarbons (CFCs) are called the greenhouse gases (GHG).
— Greenhouse effect. Heating up of the earth’s atmosphere due to the trapping of infrared radiation of longer wavelength
by carbon dioxide in the atmosphere is called the Greenhouse Effect.
— Ozone destruction. The decrease in the concentration of ozone in the upper layer of the atmosphere is called destruction
or depletion of the ozone layer.
 Ozone layer. The blanket of ozone (16 km-23 km) around the earth is called ozone layer. Ozone layer is one of the most
important life-support systems.
 Ozone hole. The zone of lower concentration of ozone in the atmosphere is called ozone hole.
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 Ozone is mainly destroyed/depleted by chlorine radical (CI ) and chlorine monoxide radical ( CIO) released during
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volcanic activity and also during reactions of ozone with NO, O and OH.