September 16 was designated by the
United Nations General Assembly as the
International Day for the Preservation of the Ozone Layer. This designation had been made on December 19, 2000, in commemoration of the date, in 1987, on which nations signed the
Montreal Protocol on Substances that Deplete the Ozone Layer.
World Ozone Day has been celebrated since 1994 and was established by the United Nations General Assembly. The day is mainly intended to spread awareness of the depletion of the Ozone Layer and search for solutions to preserve it.
The theme for the celebration of this year’s World Ozone Day to be marked on 16th September is “Keep Cool and Carry on”. The theme is accompanied by the tagline: The Montreal Protocol. The Montreal Protocol on substance that Deplete the Ozone Layer has so far been successful in phasing out of 99% of ODS globally. As a result, the abundance of ODS in the atmosphere is declining and a recent study has indicated that the ozone layer is recovering. Due to the significant reduction of ODSs globally and the starting of recovery of the ozone layer, the Montreal Protocol has been recognized as the most successful environment treaty, globally. The Protocol has been ratified by all 197 member countries of United Nations.
Ozone Layer Depletion
Ozone depletion describes two related events observed since the late 1970s : a steady lowering of about four percent in the total amount of
ozone in
Earth's atmosphere (the
ozone layer), and a much larger springtime decrease in
stratospheric ozone around Earth's polar regions. The latter phenomenon is referred to as the ozone hole. There are also springtime polar
tropospheric ozone depletion events in addition to these stratospheric events.
The main cause of ozone depletion and the ozone hole is manufactured chemicals, especially manufactured halocarbon refrigerants,
solvents,
propellants and foam-
blowing agents (
chlorofluorocarbons (CFCs), HCFCs,
halons), referred to as ozone-depleting substances(ODS). These compounds are transported into the stratosphere by the winds after being emitted from the surface. Once in the stratosphere, they release halogen atoms through
, which
the breakdown of ozone (O3) into oxygen (O2). Both types of ozone depletion were observed to increase as emissions of halocarbons increased.
Ozone depletion and the ozone hole have generated worldwide concern over increased cancer risks and other negative effects. The ozone layer prevents most harmful
wavelengths of
light (UV light) from passing through the
. These wavelengths cause
,
and
, which were projected to increase dramatically as a result of thinning ozone, as well as harming plants and animals. These concerns led to the adoption of the
in 1987, which bans the production of CFCs, halons and other ozone-depleting chemicals.
The ban came into effect in 1989. Ozone levels stabilized by the mid-1990s and began to recover in the 2000s. Recovery is projected to continue over the next century, and the ozone hole is expected to reach pre-1980 levels by around 2075.The Montreal Protocol is considered the most successful international environmental agreement to date.
Because all sunlight contains some UVB, even with normal stratospheric ozone levels, it is always important to
.
UVB radiation affects the physiological and developmental processes of plants. Despite mechanisms to reduce or repair these effects and an ability to adapt to increased levels of UVB, plant growth can be directly affected by UVB radiation.
Indirect changes caused by UVB (such as changes in plant form, how nutrients are distributed within the plant, timing of developmental phases and secondary metabolism) may be equally or sometimes more important than damaging effects of UVB. These changes can have important implications for plant competitive balance, herbivory, plant diseases, and biogeochemical cycles.
Phytoplankton forms the foundation of aquatic food webs. Phytoplankton productivity is limited to the euphotic zone, the upper layer of the water column in which there is sufficient sunlight to support net productivity. Exposure to solar UVB radiation has been shown to affect both orientation and motility in phytoplankton, resulting in reduced survival rates for these organisms. Scientists have demonstrated a direct reduction in phytoplankton production due to ozone depletion-related increases in UVB.
UVB radiation has been found to cause damage to early developmental stages of fish, shrimp, crab, amphibians, and other marine animals. The most severe effects are decreased reproductive capacity and impaired larval development. Small increases in UVB exposure could result in population reductions for small marine organisms with implications for the whole marine food chain.
Increases in UVB radiation could affect terrestrial and aquatic biogeochemical cycles, thus altering both sources and sinks of greenhouse and chemically important trace gases (e.g., carbon dioxide, carbon monoxide, carbonyl sulfide, ozone, and possibly other gases). These potential changes would contribute to biosphere-atmosphere feedbacks that mitigate or amplify the atmospheric concentrations of these gases.
Synthetic polymers, naturally occurring biopolymers, as well as some other materials of commercial interest are adversely affected by UVB radiation. Today's materials are somewhat protected from UVB by special additives. Yet, increases in UVB levels will accelerate their breakdown, limiting the length of time for which they are useful outdoors.
