Dear Kabilanji,
You have asked a good question. The polar ozone hole example shows how the whole world is
interconnected and how pollution in one place can affect an entirely different place.
Ozone depleting substances (ODS) Chlorofluorocarbons (CFCs), HCFCs
and halons, which are used in aerosol sprays, refrigerators and ACs; methyl bromide and
carbon tetrachloride (both pesticides) and methyl chloroform, a solvent. Now, the Earth's
atmosphere is continuously stirred. So, although ODS are mostly in the Northern
Hemisphere, they travel and some amount of ozone depletion is taking place everywhere.
So, why is there such a big ozone hole (23 million sq km at one
point) above Antarctica in the Southern hemisphere? Thats because of the extreme cold.
Antarctica's temperature falls below -78°C. In winters the region gets isolated due to a
special wind pattern called the polar vortex that keeps the cold air trapped over the
region and prevents it from mixing with warmer air from other regions of the globe leading
to the formation of clouds of nitric acid and water called polar stratospheric clouds
(PSC). These clouds are the medium on which reservoir chlorine compounds are converted
into ozone-destroying chlorine radicals. Chlorine cannot destroy ozone without the
addition of UV light, which is absent in winters. So, their concentrations rise until the
sun appears during the spring, when the chlorine is rapidly converted to chlorine monoxide
followed by rapid set of reactions, destroying upto 70% of the ozone in the lower
stratosphere (where ozone is situated) in weeks!
So why isn’t there a similar hole above the Arctic in the
Northern hemisphere? Thats simply because the Arctic isn’t as cold as Antarctica.
But with global warming, we could soon have an ozone hole there
too. For, a peculiar aspect of global warming that even though it increases the
temperature at the Earth's surface, temperatures in the lower stratosphere decrease to
lower temperatures triggering the ozone depletion reactions.
Dear Sureshji,
Chlorine is very good in cleaning bathrooms and fabrics and
also used for disinfecting water; but use of chlorine produces by-products which are very
toxic and harmful and put immense pressure on the eco-system.
The government still uses chlorine for water treatment as it is
the cheapest, most easily available and effective way of killing microbes. But this use
also produces disinfectant by-products (DBPs) which can cause cancer and other diseases.
Since in India millions die due to water borne diseases and costly
safe water cannot be provided to all, a rational trade-off has been done wherein using
chlorine saves far more lives by protecting people from water borne diseases, than causing
some diseases due to DBPs which are far less in numbers. Therefore, CSE as a organisation
is not against chlorine use in water treatment but against chlorine use in other products
where they can be easily substituted and phased out such as chlorine-based solvents in
industries because they are very toxic and pollutes the water ways. Also alternatives
exists for replacing these solvents. We are against use of PVCs (plastics) because they
accumulate in environment. We are against use of chlorinated pesticides because they are
very toxic and bioaccumulative. They accumulate in body fats and causes diseases like
cancer. Chlorinated compounds also damage the fertility system. Hence we need to
rationalise the use of chlorine. Where the benefits (economical, social, health and
environment) is more than drawbacks we should promote the use of chlorine, as is the case
in treating drinking water in India. But where the drawbacks overwhelm the advantages we
should get rid of it.
