Air pollution is a widely known problem which can have significant effects on
plant health. In this regard, pollutants such as air particulates, ozone, nitrogen
oxides, Sulphur dioxides have a negative impact on plant physiology
and morphology.
Ozone is found both in the troposphere as well as in the stratosphere. The
stratospheric ozone layer is naturally occurring jacket of ozone molecules while
most of the tropospheric ozone is formed via manmade sources
.Stratospheric ozone is helpful in protecting biosphere, but the
tropospheric ozone is harmful to the plants and human health.
Ozone (O3) is a reactive gas that exists in two layers of the atmosphere: the
stratosphere (upper layer) and the troposphere (at ground level and up to
15km)
Recently, it has been noticed that most of the plant species are affected
by tropospheric ozone and particulate matter.
Ozone is heavier than air it is brought down from the stratosphere by
vertical winds produced during electrical storms .However, the tropospheric ozone
is produced when sunlight reacts with nitrogen oxides and hydrocarbons emitted
by the combustion of coal or petroleum fuels (Finlayson-Pitts and Pitts,
1997). Ozone levels can be relatively constant throughout the day and night .
Tropospheric ozone is of universal curiosity as when oxidant levels in the air are
high at that particular time range the most of the air is ozone ( >90%). These levels
are usually at their highest point in the afternoon and are relatively low at night
(Atkinson, 2000). Plants are another major source of VOCs (volatile organic
chemicals)
Ozone has been shown to be harmful to human health, vegetation and crop
productivity
Due to different weather conditions NOx and VOCs both easily transported
to long distance and react to form ozone in the atmosphere, where it can persist for
many weeks. Ambient concentrations of ozone are maximum during calm,
sunny, spring and summer days when primary pollutants from urban areas are
present. Rural areas have high ozone level as compared to the urban areas, while at
high altitude the main source of OH∙ (the major tropospheric oxidant) and
as well as its action as a greenhouse
Gas-Phase Chemistry of Tropospheric Ozone
Figure 1 is a diagram of gas-phase ozone chemistry in the troposphere
highlighting the union between the cycles of O3, HOx, and NOx. Ozone is
transported from the stratosphere to troposphere via stratosphere-Troposphere
exchange (S-T exchange). Dry deposition removes it on to the surfaces. A
fraction is consumed in a chemical reaction within the troposphere.
Ozone was first described to have toxic effects on plants in the form of foliar injury
and suppressed growth in grape (Vitus sp.) (Richards et al., 1958).
Researchers have found that ambient ozone concentrations significantly reduces
the yields of susceptible crops, that leads to significant crop loss, and many
countries can further have adverse economic implications.
A schematic diagram of the sources and sinks of ozone in the troposphere.
Damaging effect ozone may be the highest during afternoon period when
its ambient concentration are high
FIG Cycle showing formation of ground-level ozone in the troposphere and the emission sources of
different precursor molecules.
What is Climate Change?
Climate change refers to significant, long-term changes in the global
climate.
The global climate is the connected system of sun, earth and oceans, wind,
rain and snow, forests, deserts and savannas, and everything people do,
too. The climate of a place, say New York, can be described as its rainfall,
changing temperatures during the year and so on.
What is Global Warming?
Global warming is the slow increase in the average temperature of the
earth’s atmosphere because an increased amount of the energy (heat)
striking the earth from the sun is being trapped in the atmosphere and not
radiated out into space.
The earth’s atmosphere has always acted like a greenhouse to capture the
sun’s heat, ensuring that the earth has enjoyed temperatures that permitted
the emergence of life forms as we know them, including humans.
Without our atmospheric greenhouse the earth would be very cold. Global
warming, however, is the equivalent of a greenhouse with high efficiency
reflective glass installed the wrong way around.
Ozone depletion and climate change
Climate change and the depletion of the stratospheric ozone layer have been
leading environmental issues for more than a quarter of a century
The amount of ultraviolet radiation (UV)† received at Earth’s surface has
important implications for human health, terrestrial and aquatic ecosystems,
biogeochemical cycles, air quality, and damage to materials, Increases in UVB due
to decreasing ozone amounts were observed during the 1980s and 1990s,
particularly at high latitudes (>~60), where ozone depletion was more pronounced.
However, because of the success of the Montreal Protocol‡ in reducing the ozone
depleting substances (ODSs), ozone is no longer decreasing and at unpolluted sites,
unaffected by changes in cloud cover, the increases in UV have not continued in
recent years. By the end of the 21st century, amounts of ozone in most regions are
expected to be greater than they were before ozone depletion began prior to 1980.
Therefore, in the absence of changes in other factors, UV-B would be expected to
decrease. However, at some locations it is possible that UV will remain elevated
due to decreasing extinctions by clouds and aerosols, particularly if the combustion
of fossil fuels is significantly reduced by that time. In some regions, such as at high
latitudes, where increases in cloud cover and reduction of the area of snow or ice
are projected as a consequence of climate change, decreases in UV at the surface
may be expected.
It is well known that UV radiation can have harmful effects on human health (e.g.,
skin cancer and eye damage), terrestrial and
aquatic ecosystems and materials. However, UV radiation also has beneficial
effects, for example by stimulating the production
of vitamin D in humans and other animals (adverse and beneficial effects .At mid-
and high latitudes, wintertime UV is very low, and human populations may be at
risk from insufficient vitamin D, a risk which may increase further if ozone
increases in the years ahead and if the current trend toward indoor living continues.
However, on the negative side, future reductions in GHGs arising from this
Montreal Protocol “windfall” will be slower, leading to more rapidly increasing
climate impacts from the main GHGs in the future. Further, the concentrations of
hydrofluorocarbons (HFCs), which are replacements for CFCs and are also GHGs,
are increasing rapidly. By 2050, the increased climate forcing from these HFCs
will exceed the reduction in climate forcing due to the phase-out of CFCs. It has
been suggested that rapid action to curb further emissions of HFCs may be among
the most effective means of limiting climate change
in the next few decades.
