The addition of any harmful substance into the environment that alters the original form of the environment is called pollution.
When one or more pollutant is added to the environment which causes an imbalance in the environment is called Air pollution ‘or’ When any substance is present in the air in a considerable amount that alters its physical, chemical or biological property and poses threat to life is called air pollution.
Sources of Air Pollution −
Burning of fossil fuels
Increasing industrial activity which is responsible for the release of harmful gases into the air.
Deforestation
Increase in the mining activities
Release of Chloro fluoro carbon from the fridges and Air conditioners.
Volcanoes and Wildfires.
Burning of garbage waste in an open area.
Urbanisation
Effects of Air pollution −
It is responsible for various respiratory, skin and GIT diseases.
Responsible for heavy smoke and fog in the urban areas
It is also responsible for property damage which occurs due to corrosion from acidic compounds present in the polluted air.
It also causes damage to vegetation.
Global warming
Ozone layer depletion
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Air pollutants are artificial or natural substances which are responsible for any physical, chemical or biological change in the environment. Air pollutants are of two types i.e.- “Criteria air pollutants” and “Hazardous air pollutants”. Criteria air pollutants are used to check the air quality standard of a particular region whereas Hazardous pollutants are the compounds which are responsible for causing cancer and other human chronic diseases. Hazardous air pollutants are also known as “Air toxins”. Fire hazards and corrosivity are some of the chemical hazards.
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Some of the air pollutants are listed below −
Carbon monoxide (CO) − When any carbon-containing substances undergo incomplete combustion i.e; in automobile industries etc, carbon monoxide is released as a by-product. It is a colourless and odourless gas. Apart from incomplete combustion, it is also released from some biological and non-biological sources.
Harmful effects of CO on human health − CO have a high affinity for Haemoglobin (240-270 times more than oxygen), thereby reducing the oxygen-carrying capacity of haemoglobin in the body organs. Due to this exposure oxygen cannot be delivered to the various body organs such as the heart, brain etc which ultimately leads to headaches, fatigue and blurred vision.
Sulphur dioxide − $\mathrm{SO_2}$ is one of the various forms of sulphur which is present in the atmosphere. The other forms of sulphur include $\mathrm{H_2S,\:H_2SO_4}$ and salts of sulphate. When sulphur-containing fossil fuels undergo combustion, coal and petroleum are burned, and $\mathrm{SO_2}$ is produced as a byproduct. It is also colourless and corrosive in nature. When sulphur trioxide reacts with water it results in the formation of sulphuric acid which is known as the "King of Acids". Harmful effects of $\mathrm{SO_2}$ on human health. It is responsible for various pulmonary diseases.
Nitrogen dioxide $\mathrm{(NO_2)}$ − It is formed as a result of high-temperature combustion and when some bacteria in the soil act on the nitrogen-containing compounds during the nitrogen cycle. When nitrogen dioxide combines with the water, it forms nitric acid which is responsible for acid rain. Acid rain is responsible for the destruction of property.
The harmful effect of $\mathrm{NO_2}$ on human health: It is also responsible for various acute and chronic pulmonary diseases.
Particulate matter − A mixture of organic and inorganic compounds are together termed Particulate matter. The source of their secretion may be natural (dust, storms, etc.) or man-made (Burning of domestic coal, etc.)
Ground level ozone − When nitrogen oxide reacts with volatile organic compounds in the presence of sunlight, it results in the formation of ground-level ozone. It is mainly responsible for global warming.
It affects the function of the lungs and causes breathing problems (Asthma).
All these five pollutants together form smog - a combination of smoke and fog. There are two types of smog- Reducing smog (which contains $\mathrm{SO_2}$ and particulate) and photochemical smog (Ozone and other oxidants).
The plant damaging substances are called phototoxicant. Various phototoxicant includes- $\mathrm{SO_2,F,HF,O_3,Cl,HCl,NH_3}$ etc.
$\mathrm{SO_2}$ and HF are responsible for the leaching of leaves and necrosis, affecting the rate of photosynthesis but HF is 10 times stronger than $\mathrm{SO_2}$
$\mathrm{O_3}$ is responsible for retarding the growth of plants, premature ageing, necrosis and bleaching.
$\mathrm{HCl}$ and $\mathrm{NH_3}$ are responsible for the development of chlorotic margins and also cause necrosis.
Atmospheric pollutants can have a negative impact on vegetation. This impact can be directly toxic or indirect (Alteration in the pH of soil and absorption of toxic salt metal salts like Aluminium). This affects the growth of vegetation. Air pollution also affects the habitat of vegetation and affects their ability to respire, thus posing threat to the environment.
Plants residing near industrial areas or on the highways tend to absorb the pollutants at the surface of their foliage. Due to air pollutants, various changes occur in the leaf structure which is as follows −
The size of stomata decreases.
The density of the leaf increases.
There occurs deposition of black phenolics in the mesophyll cells of the leave.
Many pollutants such as ozone are responsible for the development of lesions at the upper surface of leaves.
Cl is responsible for the development of lesions on the margins and between the veins.
Oxides of nitrogen are responsible for the development of black spots on the surface of leaves.
Ethylene causes epinasty of leave, abscission of leaf and chlorosis of leaf.
PAN mainly attacks young leaves and is responsible for bronzing the lower surface of leaves.
Pollution refers to any change in the physical, chemical, or biological properties of the environment. There are different types of pollution -Air pollution, water pollution, noise pollution, marine pollution etc. Air pollution refers to the addition of any substance that is harmful to human health and other organisms. Some of the causes of air pollution include deforestation, urbanisation, Industrialization etc. Air pollution is responsible for various diseases such as asthma, headache, and other pulmonary diseases. Air pollutants are the substances which cause pollution. Some of the air pollutants include $\mathrm{SO_2, NH_3,CO,O_3}$ etc. These pollutants affect the vegetation of an area and change the structure of leaves.
Q1. What is Chlorosis?
Ans: Chlorosis refers to the loss of chlorophyll.
Q2. Name some minor industrial pollutants.
Ans: Benzene, mercury and asbestos.
Q3. What is epinasty?
Ans: Epinasty refers to the downward bending of the leaf when there is excessive growth on the upper side of the leaf.
Q4. What does AQI stand for?
Ans: It stands for Air quality index which is used for assessing daily air quality.
Q5. How is AQI value related to air pollution?
Ans: More the AQI value, the more the pollution.
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