موضوع
عن التلوث بالانجليزي the pollution
موضوع عن التلوث بالانجليزي the pollution
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Main regulated
pollutants:
O3 (Ozone)
Ozone is a
secondary pollutant formed in the lower atmosphere from a mixture of gaseous
precursors composed of nitrogen oxides and volatile organic compounds. These
pollutants required to produce ozone are mainly emitted by human activities.
and also by vegetation. Solar radiation controls the intensity of ozone
production.
High surface
concentrations therefore occur in the summer period when sunshine is important
and when the weather conditions are not very dispersive and promote
accumulation. Generally it is during a weather situation under anticyclonic
influence that episodes of pollution with ozone are observed. The episode will
be even more important if the anticyclonic situation persists.
Ozone has a
lifespan of a few days in the lower layers of the atmosphere, so it can be
transported far from its production area: this pollution is usually observed
more intensively in peri-urban areas and rural downwind of agglomerations.
Ozone from
the lower atmosphere affects ecosystems and human health. It therefore has a
toxic effect which is to oppose the role of stratospheric ozone whose
significant concentrations are located at more than 10 km altitude and which
filters a harmful part of the ultraviolet rays of solar radiation. Ozone is an
aggressive gas that penetrates deep into the lungs and can react to cellular
components and affect respiratory capacity. These effects are accentuated by
the presence of other pollutants such as oxides of sulfur and nitrogen, or
during physical exertion and prolonged exposure. Ozone has a detrimental effect
on vegetation (crop yield, for example) and on some materials.
The chemical
production of an ozone molecule (O3) is always the result of a reaction between
a molecule of oxygen (O2) and an oxygen atom (O). It is the photodissociation
of nitrogen dioxide (NO2) that produces the required oxygen atom (O), provided
that the nitric oxide (NO) reacts with a hydroperoxyl (HO2) radical rather than
with O3, which would have a zero balance. In low-pollution areas, HO2 is
derived from the oxidation of carbon monoxide (CO) and methane (CH4) present in
the natural atmosphere. But in polluted areas, the production of ozone is
favored, because the oxidation of volatile organic compounds (VOCs) is faster
than that of CO or CH4. In highly polluted zones, and under certain conditions
of insolation, the high concentrations of NOx, can lead to nocturnal
destruction of ozone (titration effect).
NOx
(Nitrogen oxides)
The family
of nitrogen oxides groups mainly nitrogen dioxide (NO2) and nitric oxide (NO).
NOx is mainly emitted during high temperature combustion; whether by oxidation
of the nitrogen present in the fuel or by fixing the nitrogen present in the
air at very high temperature. Combustion generally emits NO, part of which is
oxidized to NO2 directly in the combustion chamber, and another part continues
its oxidation in the atmosphere. NOx are precursors of ozone, as well as some
strong acids, responsible for acid rain events.
Among the
main emitting sectors of NOx, the road sector is predominant (56% of national
emissions in 2011), followed by manufacturing (14% in 2011) and agriculture /
forestry (10% in 2011). Large combustion plants and the residential / tertiary
sector are also major contributors.
VOCs
(Volatile Organic Compounds)
VOCs are
gases composed of at least one carbon atom, combined with one or more of the
following: hydrogen, halogen, oxygen, sulfur, phosphorus, silicon or nitrogen.
There is often methane (CH4), which is the most common VOC in the atmosphere
but is not directly harmful to health or the environment but is, on the other
hand, a greenhouse gas. The rest of the VOCs are commonly referred to as NMVOCs
(Non-Methane Volatile Organic Compounds). VOCs are precursors of ozone and fine
particles (secondary organic aerosols).
Anthropogenic
NMVOCs are emitted during combustion phenomena but also by the evaporation of
solvents (contained in paints for example), fuels, etc. There is a very large number
of VOCs that can be either directly emitted or produced in the atmosphere.
The main
sectors emitting VOCs are the residential sector (38% of emissions in 2011) due
to the use of solvents for domestic use or in the building industry, the
manufacturing industry (paints), then the transportation, the transformation of
the energy then agriculture / forestry.
