|Class 11 Chemistry Environmental Chemistry||Air pollution|
“The contamination of air with harmful and undesirable substances “
Sources of pollutants:
Natural –like volcanic eruption, pollen grains, forest fires, etc.
The atmospheric pollution is basically contamination of troposphere and stratosphere.
Troposphere is mainly polluted by:
There are five major pollutants of troposphere are like Carbon dioxide, Carbon monoxide etc.
Carbon monoxide: It is colourless and odourless gas and it is released in air by human activities like:
Though the CO is produced still its level do not rise in atmosphere because of conversion of CO to carbondioxide by the bacteria present in soil so we can say microorganisms act as a sink for carbon monoxide but this sink is not available in urban areas due to less soil.
Effects of carbon monoxide:
The carbon monoxide is a poisonous gas if inhaled can combine with haemoglobin (Hb) to form defective type of complex that can lead to suffocation and also deathTherefore it is a fatal gas.
Carbon dioxide: it is released in atmosphere due to burning; respirationetc.Excess of it is removed by plants as they utilize it for photosynthesis.However, increased in its concentration leads to global warming.
Green House Effect
Global warming “is the increase in the concentration of certain gases like carbon dioxide, methane, etc. in air due to which infra-red rays get trapped in it and it leads to increase in overall temperature of earth.”
Oxides of Sulphur:They are produced by burning of Sulphurcontaining fossil fuels. This Sulphur dioxide can cause respiratory problems like asthma, emphysema, irritation to eyes, redness in eyes etc.
Oxides of nitrogen: The nitrogen oxides are formed due to lightning strikes at higher altitudes and also due to burning of fossil fuels.It causes irritant red haze, damage leaves of plant, retard rate of photosynthesis also respiratory disorders.
Both Sulphur dioxide and nitrogen dioxide are cause of acid rain
When rain falls, these gases combine and the following reaction takes place:
SO2 + H2O H2SO4
NO2+ H2O HNO3
As a result, rain water no longer remains only pure water it becomes acidic
Hydrocarbons:They are produced due to combustion of fuels are actually carcinogenic that causes cancer. They also harm plants as they cause ageing in plants, shedding of leaves etc.
Chlorofluorocarbons:They are released into the atmosphere from industries. They are actually manmade industrial chemicals used in air conditioners, refrigeratorsetc. and their vapours do not remain in lower layers of atmosphere they move up and cause thinning of ozone.
Ozone: It is a molecule consisting of three oxygen atoms i.e. O₃. It is present in stratosphere.
Ozone is formed when u-v rays in upper atmosphere split oxygen atoms that are: -
When oxygen molecule splits into atoms then each atom combine with undissociated molecule of oxygen to form ozone.
Ozone protect us from ultra violet radiations as it doesn’t allow ultra violet rays to enter earth’s atmosphere that if enter into earth may harm us in many ways such as:
For this some synthetic chemicals are responsible like ChloroFloro Carbons that are used in refrigerators, air conditioners, etc.
Now, instead of using CFC’s; HFC’S and PFC’s are used that is somehow helping in saving the ozone layer.
Non-viable particulates are classified according to nature and size of particles. They are as follows:-
Smoke: Itconsists of solid and liquid particles formed during combustion of fuels etc.
Dust: It is composed of fine solid particles produced during crushing, grinding of solid particles, like saw dust from wood, fly ash from factories etc.
Mist:They are produced by particles of spray liquids and condensation of vapors in air, like insecticides etc.
Fumes:They are obtained by condensation of vapors during sublimation, distillation, boilingetc., like metallic and non-metallic oxides
Smog and Photochemical smog
Harmful effects of photochemical smog
Photochemical smog can be controlled as:-