Background
Air pollution can be defined as the presence
in the outdoor or indoor atmosphere of one or
more gaseous or particulate contaminants in quantities,
characteristics and duration such as to be injurious
to human, plant or animal life or to property,
or which unreasonably interferes with the comfortable
enjoyment of life and property.
Air pollution problems may vary
greatly with the geography, demography and the
socio-economic profile of a region, which will
determine the source and emission rate of the
pollutant. The climate and topography a region
will influence the distribution and atmospheric
processes of the pollutant and ultimately its
effect on the environment and human health.
Sources
- Carbon
dioxide (CO2): Carbon dioxide is not by
definition an air pollutant but a natural component
of the atmosphere. Increasing emissions of CO2
in the atmosphere over the past 100 years resulted
in global warming by the following process:
CO2 is transparent to short-wave solar radiation
but absorbs infrared radiation and traps it
in the lower atmosphere. This phenomenon is
known as the "green house effect".
- Carbon
monoxide (CO): Carbon monoxide is one of
the most common and widely distributed air pollutants.
There is evidence to suggest that global emissions
of CO have risen in line with the massive growth
of motor vehicle numbers and mileage. Concentrations
inside motor cars often exceed those in the
surrounding atmosphere. Forest clearance, savanna
burning and the oxidation of methane are the
other sources of CO.
- Sulphur
dioxide (SO2): Man-made emissions include
fossil fuel combustion, power plants and industries.
Natural emissions form from soil, plants, the
burning of biomass, marine biogenic sea spray
and volcanoes.
-
Particulate matter: On a global scale
particulate matter is one of the most prevailing
atmospheric pollutant. Natural sources include
wind blown dust, sea spray, pollen, forest fires
and volcanoes. The following are some of the
natural and man-made emissions for the different
particulate matter:
| a. |
Fine particulate matter (up to 2 ?m): Combustion,
gas particles condensation and conversions
mainly from from SO2 and NOx. |
| b. |
Large
particles (2 -100 ?m): They are usually natural
particles or industrial dust. |
| c. |
Black elemental carbon particles: Diesel vehicle
emissions and Coal use. |
| d. |
Toxic
trace metals in the particulate fraction:
Potentially toxic trace metals such as As,
Pb, Cd and Hg from metals melting and coal
combustion. |
| e. |
Lead in the particulate fraction: Forms from
using Lead (Pb) as an anti-knock petrol additive,
paint pigment and in the manufacturing of
batteries. |
| f. |
Polynuclear
(Polycyclic) aromatic hydrocarbons (PAH):
A large group of organic compounds with two
or more benzene rings formed by pyrolytic
processes resulting from incomplete combustion
and are very often absorbed on to particulate
matter. Shipping, heavy industry, biomass
burning, heating with coal are the other sources
of man-made emissions. Carbonization is the
principle natural source. |
-
Hydrocarbons: Petrol and Diesel fuel
consists of a large number of hydrocarbons.
Aromatic hydrocarbons are added to petrol to
aid refining. In some countries large quantities
of alcohol or ethanol are added to petrol which
give rise to large numbers of Volatile Organic
Compounds (VOCs).
-
Nitrogen Oxides (NOx): They are significant
pollutants on both local and regional scale.
NOx emissions result from fossil fuel combustion
and half of these man-made emissions are from
mobile sources. Natural production is from bacterial
action in soils, lightning and forest fires.
- Photochemical
Smog: Nitrogen oxide and other primary pollutants
react under certain climatic conditions to form
secondary pollutants such as NO2, O3 and peroxyacyl
nitrates (PANs). These photochemical oxidants
in combination with various organic compounds
are referred to as "photochemical smog".
Human
Impact
Most atmospheric pollutants pose a
risk to human health. Health effects vary according
to the intensity and duration of exposure and
health status of the population exposed. In recent
years, a growing body of scientific evidence has
indicated that indoor air can be more seriously
polluted than outdoor air, even in cities with
relatively poor air quality. People spend approximately
90% of their time indoors, therefore it is likely
that the risk to the health may be greater due
to air pollution indoors. The most susceptible
members are the very young, the elderly and the
chronically ill who spends the longest periods
indoors.
Environmental
Impacts
It
is now generally accepted that the increase in
atmospheric CO2 together with other green house
gases, CH4, N2O, O3 and CFCs leads to an increase
in average global temperature. This will alter
global weather patterns, ocean currents with an
expected rise of mean sea level 30 to 50 cm by
the year 2050. Thus, effecting world agriculture
and marine ecosystems. Other impacts include the
deposition of many air pollutants in the marine
environment and the atmospheric oxidation and
hydrolysis of others to form acidic precipitation.
Many gaseous pollutants also inhibit plant growth
and development and cause direct damage to various
structures and materials.
Control
Strategies
Strategies for controlling air pollution depends
upon national and regional authorities setting
air quality and emission standards. By requiring
adherence to such a set of performance standards
governments can encourage industry to develop
new and better technologies.
Air
Pollution in the Arab World
Coming
Soon !
References
Used
UNEP
1992. Chemical Pollution: A Global Overview
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