● The `color{brown}("‘bad ozone’")` is formed in the lower `color{violet}("atmosphere (troposphere)")` that harms`color{violet}(" plants")` and `color{violet}("animals.")`

● There is `color{brown}("‘good ozone’")` also; this `color{violet}("ozone")` is found in the upper part of the atmosphere called the `color{brown}("stratosphere"`, and it acts as a shield absorbing `color{violet}("ultraviolet radiation")` from the `color{violet}("sun.")`

● `color{violet}("UV rays")` are highly injurious to `color{violet}("living organisms")` since `color{violet}("DNA")` and proteins of `color{violet}("living organisms")` preferentially absorb UV rays, and its high `color{violet}("energy breaks")` the `color{violet}("chemical bonds")` within these molecules.

● The thickness of the `color{violet}("ozone")` in a column of air from the ground to the top of the atmosphere is measured in terms of `color{brown}("Dobson units (DU).")`

● `color{violet}("Ozone gas")` is continuously formed by the action of `color{violet}("UV rays")` on `color{violet}("molecular oxygen")`, and also `color{violet}("degraded")` into `color{violet}("molecular oxygen")` in the `color{violet}("stratosphere.")`

● There should be a balance between production and `color{violet}("degradation of ozone")` in the stratosphere.

● Of late, the balance has been disrupted due to enhancement of `color{violet}("ozone degradation")` by `color{brown}("chlorofluorocarbons (CFCs).")`

● `color{violet}("CFCs")` find wide use as `color{violet}("refrigerants.")`

● `color{violet}("CFCs")` discharged in the `color{violet}("lower part")` of atmosphere move upward and reach stratosphere.

● In stratosphere, `color{violet}("UV rays")` act on them releasing `color{brown}(Cl "atoms.")`

● `color{violet}(Cl "degrades ozone")` releasing molecular `color{violet}("oxygen,")` with these atoms acting merely as `color{brown}("catalysts;")` Cl atoms are not consumed in the reaction.

● Hence, whatever `color{violet}("CFCs")` are added to the `color{violet}("stratosphere,")` they have permanent and continuing affects on `color{violet}("Ozone levels.")`

● Although `color{violet}("ozone depletion")` is occurring widely in the stratosphere, the `color{violet}("depletion")` is particularly marked over the `color{violet}("Antarctic region.")`

● This has resulted in formation of a large area of `color{violet}("thinned ozone layer")`, commonly called as the `color{brown}("ozone hole.")`

● `color{violet}("UV radiation")` of wavelengths shorter than `color{brown}("UV-B")`, are almost completely absorbed by `color{violet}("Earth’s atmosphere,")` given that the ozone layer is intact.

● But, `color{violet}("UV-B")` damages `color{brown}("DNA")` and mutation may occur.

● It causes aging of `color{violet}("skin, damage")` to `color{violet}("skin cells")` and various types of skin cancers.

● In human eye, cornea absorbs `color{violet}("UV-B radiation,")` and a high dose of `color{violet}("UV-B")` causes inflammation of cornea, called `color{brown}("snow-blindness")` cataract, etc.

● Such exposure may permanently `color{violet}("damage the cornea.")`

● Recognising the `color{violet}("deleterious affects")` of `color{violet}("ozone depletion")`, an international treaty, known as the `color{brown}("Montreal Protocol,")` was signed at Montreal (Canada) in 1987 (effective in 1989) to `color{violet}("control the emission")` of `color{violet}("ozone depleting substances.")`

● Subsequently many more efforts have been made and protocols have `color{violet}("laid down")` definite `color{violet}("roadmaps, separately")` for developed and developing countries, for `color{violet}("reducing the emission of CFCs")` and other `color{violet}("ozone depleting chemicals.")`

● The `color{violet}("degradation")` of natural resources can occur, not just by the action of `color{violet}("pollutants")` but also by `color{violet}("improper resource utilization")` and maintenance practices including:

`star` `color{green}("Soil erosion and desertification")`
`star` `color{green}("Waterlogging and soil salinity")`
`star` `color{green}("Deforestation")`

● The development of the fertile top-soil takes centuries.

● But, it can be `color{brown}("removed very easily")` due to human activities like `color{violet}("over-cultivation,")` unrestricted grazing, `color{violet}("deforestation")` and`color{violet}(" poor irrigation")` practices, resulting in arid patches of land.

● When large barren patches extend and meet over time, a `color{violet}("desert is created. ")`

● Internationally, it has been recognised that `color{brown}("desertification")` is a major problem nowadays particularly due to `color{violet}("increased urbanisation.")`

● Irrigation without proper drainage of `color{violet}("water leads")` to `color{brown}("waterlogging in the soil.")`

● Besides affecting the `color{violet}("crops, waterlogging draws salt")` to the `color{violet}("surface of the soil.")`

● The `color{violet}("salt")` then is deposited as a `color{violet}("thin crust")` on the `color{violet}("land surface")` or starts collecting at the roots of the `color{violet}("plants.")`

● This increased `color{violet}("salt content")` is inimical to the `color{violet}("growth of crops")` and is extremely damaging to agriculture.

● `color(brown}("Waterlogging and soil salinity")` are some of the problems that have come in the wake of the `color{violet}("Green Revolution.")`