AIR POLLUTION

                                       AIR POLLUTION

                  Air pollution means the presence of air contaminants in the outdoor atmosphere such as dust, fumes, gas, mist, odor, smoke, or vapor in quantities or characteristics, and of duration, such as to be injurious to human, plant or animal life.

PHYSIOLOGICAL EFFECTS ON PLANTS:

Some of the important air pollutants and their effects on plant growth and development are 

Sulphur dioxide (SO2):

It is a primary product of the combustions of sulphur containing fossil fuels.Coal burning presently accounts for 60 per cent of the sulphur dixoxide pollution. Sulphur oxides are absorbed by water and go into solution in water. If not absorbed, it soon oxidized to the less toxic SO3 and finally to sulfuric acid mist. Sulphuric acid mists on Condensation nuclei and fall upon the vegetative canopy and affect the plant growth.

Oxides of nitrogen (NO):

These are the byproducts of combustion of atmospheric nitrogen and oxygen. The initial product of this reaction, nitric oxide (NO) is oxidized to Nitrogen dioxide (NO2), utilizing the oxygen in the atmosphere. Energy from sunlight quickly splits the NO2 back to NO and atomic oxygen which combines with the molecular oxygen of the atmosphere to form ozone (O3).

Thus, Ozone (O3) accumulates in the atmosphere. When the leaves are exposed to O3, the guard cells of the epidermis quickly lose turgor and the stomatal aperture closes. Ozone may destroy structural integrity of membranes.It damages tobacco, tomato, bean, pine etc. NO in the urban atmosphere reacts with several hydrocarbons  and thus helps in production of secondary pollutants like PAN(Peroxy Acyl Nitrates).

Carbon dioxide (CO2):

Combustion of fossil fuels and automobile exhausts increase the CO2 in the atmosphere.Continued increase in CO2 (0.5 % per annum)has a warming effect that melts the polar ice and bring changes in the ecology of seas. Large scale floods are some of the potential consequences. On the other hand, increased CO2 content could increase the rate of photosynthesis.

Carbon monoxide (CO):

It also comes mostly from exhaust fumes of motor vehicles and industrial works.At high concentrations, plants produce toxic symptoms like leaf curling, ageing and reduction in leaf size.

The CO competitively inhibits nitrogen fixation by legumes.

Fluorides:

Both gaseous and particulate fluorides are released into the atmosphere for the aluminum factories, manufacturing units of fluoride compounds, glass, pottery and brick works. Fluoride enters the plant through stomata. In intercellular spaces they dissolve in water and transported to the leaf tips and margins where it accumulates.Chloroplasts are presumed to be the major site of accumulation of fluorides.Accumulation of toxic concentrations of fluorides in broad-leaved species causes necrosis, chlorosis or both at leaf tip and margin.

 

Methyl-Isocyanate (MIC):

Methyl Iso cynate gas is deadly poisonous to human beings, animals and plants as well. It emanates from pesticide preparations and its accidental leakage.The Bhopal gas tragedy which occurred in 1984 caused complete defoliation in a variety of trees.The fruits of guava developed cracks but surprisingly mango, palms and banana were not at all affected.

CONTROL OF AIR POLLUTION:

1. Use of settling chambers, bag filters, electrostatic precipitators, gas absorbers, catalytic                          combustion agents.

2. Chimneys should be raised so that smoke and particulate matters are thrown high and are carried            by wind for dispersa.

3. Recycling of harmful chemicals and their reuse.

4. Use of high temperature incinerators for reduction in particulate ash production.

5. Generally industrial activities should be located away from residential localities.

6. Environment engineers should have say before setting up industries in particular place. Because the        nature of pollution, local conditions and meteorology may not be suitable for particular industry in         particular area.

7. Use of non-combustive sources of energy, e.g. solar power, unclear power, geothermal power, tidal        power etc.