Here we are providing the short notes on Chemistry which will be help to crack science part in may examinations like SSC, Railway and other competitive exams.
The substance which causes pollution is known as pollutant.
Pollutants are of two types
— Primary pollutants persist in the environment in the form, they are produced, e.g. sulphur dioxide (), nitrogen dioxide () etc.
— Secondary pollutants are the products of reaction of primary pollutants, e.g. peroxyacetye nitrate (PAN), ozone , aldehyde etc.
Major Gaseous Air Pollutants
Major gaseous air pollutants are oxides of sulphur, nitrogen, carbon and hydrocarbons.
It is highly toxic for both animals and plants, bronchitis, asthma, emphysema. It also causes eye and throat irritation and breathlessness.
Sulphur dioxide reduces the rate of formation of chloroplast and thus, causes chlorosis. is highly corrosive and damage buildings, marbles (Taj Mahal) and textiles.
is oxidized to which reacts with water to give remains suspended in the air as droplets or come down in the form of acid rain.
Oxides of nitrogen
Among the oxides of nitrogen, nitric oxide (NO), a colourless, odourless gas and nitrogen dioxide , a brown gas with pungent odour act as tropospheric pollutants.
is highly toxic for living tissues causes leaf fall. It is a corrosive oxide and helps in the formation of smog.
In the presence of oxygen, reacts with water or moisture and produces nitric acid which is an important factor for making acid rain.
Carbon monoxide (CO)
From more stable carboxyhaemoglobin complex with haemoglobin due to which the delivery of oxygen to the organs and tissues is blocked.
Out of the hydrocarbons, methane is the most abundant hydrocarbon pollutant. Higher concentrations of hydrocarbons given carcinogenic effect, i.e. are cancer producing. They cause ageing of plants, breakdown of plant tissues and shedding of leaves.
Consequences of Atmospheric Pollution
Green house gases such as carbon dioxide, methane and water vapours trap the heat radiated from Earth. This leads to an increase in Earth’s temperature. This heating up of Earth and its objects due to the trapping of infrared radiation by green house gases in the atmosphere, is called green house effect.
Green house effect is very essential for the existence of life because in its absence, Earth would be converted into extremely cold planet. When concentration of green house gases increases, green house effect also increases. This is known as global warming.
It is caused by the presence of oxides of nitrogen and sulphur in the air. These oxides dissolve in rain water and from nitric acid and sulphuric acid respectively. The rain carrying acids, is called acid rain.
Diseases caused by particulate
|Pneumoconiosis||Due to inhalation of coal dust|
|Silicosis||Due to inhalation of free silica ()|
|Black lung disease||Found in workers of coal mines|
|White lung disease||Found in textile workers|
|Byssinosis||Due to inhalation of cotton fibre dust|
It is two types:
These occur in cool, humid climate. Sulphur dioxide and particulate matter from fuel combustion are the main components of classical smog.
These occur in warm, dry and sunny climate. It consists of a mixture of primary pollutants (nitrogen oxides and carbon monoxides) and secondary pollutants (ozone, formaldehyde).
Peroxyacetyl nitrate (PAN) and aldehydes present in smog causes irritation in eyes. PAN has the highest toxicity to plants. It attacks younger leaves and causes bronzing and glazing of their surfaces.
In stratosphere, ozone layer absorbs the ultraviolet radiation of the Sun which are harmful to living organisms.
Depletion of ozone layer causes skin cancer and cataract in human and reduction of planktons in ocean and depletion of plants.
Depletion of ozone layer is caused by chlorofluoro carbons which are used in refrigeration, fire extinguishers and aerosol sprayers.
In stratosphere, the depletion of ozone layer leading to ozone hole has been mainly observed in the stratosphere of Antarctica.
The formation of this hole occur due to the accumulation of special clouds in the region called Polar Stratospheric Clouds (PSCs) and inflow of chlorofluoro carbons (CFCs).
In some part of India, drinking water is contaminated by the impurities of arsenic, fluoride, uranium, etc.
In water, some dissolved Oxygen (DO) is also present. For a healthy aquatic life, the optimum value of DO is 5-6 ppm. If DO is below 5 ppm, the growth of fishes is inhibited.
Biochemical Oxygen Demand (BOD) is the total amount of oxygen (in mg) required by microbes to decompose the organic matter present in 1L of water sample while Chemical Oxygen Demand (COD) refers to the total amount of oxygen (in ppm) consumed by the pollutants in a water sample.
For clean water, BOD is less than 5 ppm while for highly polluted water, it is 17 ppm or more.