Acid Rain & Ozone Depleting Substances

Acid Rain

Acid rain (Ph < 5.6) is caused by emissions of sulfur dioxide and nitrogen oxide, which react with the water molecules in the atmosphere to produce acids (H₂SO₄& HNO₃). Acid rain is a popular term referring to the deposition of wet (rain, snow, sleet, fog, cloud water, and dew) and dry (acidifying particles and gases) acidic components.

Ozone depleting substances (ODS)

Scientific evidence indicates that stratospheric ozone is being destroyed by a group of manufactured chemicals, containing mainly chlorine or bromine, called “ozone-depleting substances” (ODS).
ODS are very stable, nontoxic, non-flammable and environmentally safe in the lower atmosphere, which is why they became so popular in the first place
However, their very stability allows them to float up, intact, to the stratosphere & once there, they are broken apart by the intense ultraviolet light, releasing chlorine and bromine.
Chlorine and bromine demolish ozone at an alarming rate, by stripping an atom from the ozone molecule

Main ODS – CFCs, HCFCs, Halons, CCl4, NOx, CH3CCl3 (Methyl chloroform)

Major Sources: Solvent Cleansing products >Refrigeration & Air conditioners > Foam Products

Chlorofluorocarbons (CFCs)

The most widely used ODS, accounting for over 80% of total stratospheric ozone depletion.
Used as coolants in refrigerators, freezers and air conditioners in buildings and cars manufactured before 1995.
Also found in industrial solvents, dry-cleaning agents and hospital sterilants.
Also used in foam products — such as soft-foam padding (e.g. cushions and mattresses) and rigid foam (e.g. home insulation)

Halons & Hydrobromofluorocarbon (HBFC)

Halons, unlike CFCs, contain bromine, which destroys ozone 100 times more than chlorine
Halons are used primarily in fire extinguishers & methyl bromide (Pesticide)

Methyl Chloroform

Used mainly in industry as cleansing solvent — for vapour degreasing, cold cleaning, adhesives and chemical processing.

Carbon Tetrachloride

Mainly used as solvent & in fire extinguishers.

Hydrofluorocarbons (HCFCs)

Major, “transitional” substitutes for CFCs- much less harmful to stratospheric ozone than CFCs
But still cause some ozone destruction and are potent greenhouse gases

Impacts of Ozone Depletion

Skin cancers, sunburns and premature aging of the skin
UV radiation can damage several parts of the eye, including the lens, cornea, retina and conjunctiva
Weakening of the human immune system
Several of the world’s major crop species are particularly vulnerable to increased UV, resulting in reduced growth, photosynthesis and flowering
Plankton are threatened by increased UV radiation

Ozone hole mainly in Antarctica not in Arctic pole, because

Southern polar region more colder & isolated than north, which favor the formation of polar stratospheric clouds (PSCs) which in turn serve as platforms for catalytic ozone breakdown
As a consequence of having less land, the circulation over the Antarctic is more persistent and vortex-like, which favours PSCs
Air inside the vortex is prevented from mixing with warmer, ozone-rich air from lower latitudes (This vortex is not a feature of the Arctic)

Ozone

Ozone in atmosphere is measured in dobson unit.
A Dobson unit of gas is equal to a layer of gas, at the surface of the Earth, with a thickness of one hundredth of a millimeter
The ozone in the atmosphere is about 300 Dobsons, which means if you brought all of the ozone in the atmosphere down to a layer of pure ozone at the surface; it would be about three millimeters thick.