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Water In Ecosystems: A Non Renewable Resource
In rural areas, PAHs are present at much lower concentrations: TMC is 100 to 300
times less than in urban areas (0.3 to 2 ng.m- 3 ). The concentrations depend
considerably on the meteorological conditions and the contribution of air masses.
In Western Europe, minima are observed during rain episodes and when the humid
air masses come from the ocean, and maxima are observed when the air masses
come from the North or the North-East sector. In rural atmosphere all PAHs are
present, showing that the various pollution sources are mixed. Nevertheless, PAHs
characteristic of petrol-engined vehicles (Benzo ghi Perylene) and fuel oil
combustion (Fluoranthene and Pyrene) remain predominant in the atmospheric
aerosols.
The background level of tropical atmospheres is about the same as that in rural
European zones: TMC value is of the order of 200 pg.m- 3 (Ivory Coast). The air
quality is the same in European rural regions and in remote tropical regions, but
in the latter regions PAHs come mainly from biomass burning.
In a marine atmosphere the concentrations depend mainly on the sampling site,
the proximity of the sources and the prevailing wind. In the Mediterranean Sea,
concentrations are similar to those found in continental media (OA-5.5.ng.m- 3 ).
The many urban and industrial sites around the Mediterranean Sea explain these
relatively high levels. On the other hand, the atmosp'heric levels in the Pacific
ocean are 10 to 70 times lower (about 50 pg.m 3 ). Although low, these
concentrations are not negligible and prove that particulate PAH can be
transported over very long distances. During transport, the aerosols are diluted by
atmospheric dynamics. Rain or snow events scavenge the air masses and their
aerosol content.
These two phenomena result in a marked drop in the concentrations. Also it is
logical to find very low concentrations in receptor zones remote from the
pollution sources.
Particulate PAHs are also found in polar media (Greenland). The concentrations
are very low - at the limit of detection. The TMC is 20 pg.m- 3 . We observe
important seasonal variations, with maxima at the end of winter and minima in
summer.
The presence of significant amounts of PAHs in these regions shows that the whole
globe is contaminated by these potentially carcinogenic compounds. The PAH
profile is different from that observed in urban atmosphere or in biomass burning
aerosols. The polar PAH profile is a mixture of both; however the latter
predominate, showing the importance of the biomass burning source in the Arctic
regions.
In Arctic media, after their transport, the aerosols are deposited on the earth by
snowfall, covering the surface of the polar sheet, then accumulating in the ice. In
samples taken from surface snow the TMC value is 1350. pg.kg- i of snow and in a
deep ice core collected at the same site (75m deep), PAHs were detected in all
strata of the ice; the TMC is around a value of 800 pg.kg- i of ice.
This result proves that these compounds have been emitted, transported and
accumulated in the environment at least since the beginning of the industrial era
(200 years, corresponding to the 75 m sampled).
Water In Ecosystems: A Non Renewable Resource
In rural areas, PAHs are present at much lower concentrations: TMC is 100 to 300
times less than in urban areas (0.3 to 2 ng.m- 3 ). The concentrations depend
considerably on the meteorological conditions and the contribution of air masses.
In Western Europe, minima are observed during rain episodes and when the humid
air masses come from the ocean, and maxima are observed when the air masses
come from the North or the North-East sector. In rural atmosphere all PAHs are
present, showing that the various pollution sources are mixed. Nevertheless, PAHs
characteristic of petrol-engined vehicles (Benzo ghi Perylene) and fuel oil
combustion (Fluoranthene and Pyrene) remain predominant in the atmospheric
aerosols.
The background level of tropical atmospheres is about the same as that in rural
European zones: TMC value is of the order of 200 pg.m- 3 (Ivory Coast). The air
quality is the same in European rural regions and in remote tropical regions, but
in the latter regions PAHs come mainly from biomass burning.
In a marine atmosphere the concentrations depend mainly on the sampling site,
the proximity of the sources and the prevailing wind. In the Mediterranean Sea,
concentrations are similar to those found in continental media (OA-5.5.ng.m- 3 ).
The many urban and industrial sites around the Mediterranean Sea explain these
relatively high levels. On the other hand, the atmosp'heric levels in the Pacific
ocean are 10 to 70 times lower (about 50 pg.m 3 ). Although low, these
concentrations are not negligible and prove that particulate PAH can be
transported over very long distances. During transport, the aerosols are diluted by
atmospheric dynamics. Rain or snow events scavenge the air masses and their
aerosol content.
These two phenomena result in a marked drop in the concentrations. Also it is
logical to find very low concentrations in receptor zones remote from the
pollution sources.
Particulate PAHs are also found in polar media (Greenland). The concentrations
are very low - at the limit of detection. The TMC is 20 pg.m- 3 . We observe
important seasonal variations, with maxima at the end of winter and minima in
summer.
The presence of significant amounts of PAHs in these regions shows that the whole
globe is contaminated by these potentially carcinogenic compounds. The PAH
profile is different from that observed in urban atmosphere or in biomass burning
aerosols. The polar PAH profile is a mixture of both; however the latter
predominate, showing the importance of the biomass burning source in the Arctic
regions.
In Arctic media, after their transport, the aerosols are deposited on the earth by
snowfall, covering the surface of the polar sheet, then accumulating in the ice. In
samples taken from surface snow the TMC value is 1350. pg.kg- i of snow and in a
deep ice core collected at the same site (75m deep), PAHs were detected in all
strata of the ice; the TMC is around a value of 800 pg.kg- i of ice.
This result proves that these compounds have been emitted, transported and
accumulated in the environment at least since the beginning of the industrial era
(200 years, corresponding to the 75 m sampled).