48
H.-J. Bolle
Westrum (1999) point out that the natural regrowth of burned forests in Greece
partially depends on the grazing goats which eat leaves and suppress the recovering
of deciduous trees like Quercus species.
Often in burned areas monocultures of Pinus are re-forested rather then mixed
cultures and the carpet of fallen needles underneath suppresses undergrowths and
degrades soils by acidification.
The burning of agricultural debris as well as the wildfires are an important
source for aerosols and cause a hazy atmospheric boundary layer over large areas.
The burning thus have an impact on the radiative transfer but also an atmospheric
chemistry since with the water vapour, carbon dioxide and aerosols also large
amounts of the BVOes are set free by the fires. These fires are concentrated at the
end of the vegetation period and at the beginning of the rainy period. Some of the
material therefore is washed out and deposited at the surface. Since these are partly
acidic components it contributes to acidify the soils.
5.4 The Role of Aerosols
The aerosol content of the Mediterranean atmosphere varies largely. Few
measurements indicate that the amount of aerosol increased since the fifties at least
in some heavily industrialized areas. Aerosols interact in various ways with the
atmospheric radiative transfer and constitute an important climate factor. Dry
aerosols reduce the solar radiation at the surface and hygroscopic aerosols are
responsible for cloud formation and rain, if the moisture is present. Aerosols
furthermore interact with remote sensing from space. The limi ted knowledge of their
radiative properties and concentrations hampers the correction of satellite data. One
of the great deficits for coping with these different aspects is the lack of an aerosol
climatology for the Mediterranean basin.
Four types of aerosols are of specific importance in the Mediterranean area:
Industrial aerosols, sea-spray aerosols, sand particles, and aerosols ofbiogene origin.
They act in different ways. Hygroscopic salt particles produced by sea spray foster
the condensation as do many of the industrial aerosols. The presence of Saharan
sand particles is an outstanding feature of the Mediterranean atmosphere. Desert
sand particles are not hygroscopic and due to absorption of solar radiation they may
even warm the dusty atmosphere, dissolve clouds, and thus prevent condensation,
a process which sometimes can be observed in satellite images. Their climatic effect
primarily is the backscattering of solar radiation to space and thus the reduction of
the short wave radiant energy which reaches the surface. This counteracts the
greenhouse effect since it causes cooling at the surface. The same effect have
sulphate particles of industrial origin. On the other hand, in the thermal infrared,
they make the atmosphere more opaque which increases the long wave atmospheric
radiation. The ratio of their longwave to shortwave properties determine which of
the effects dominates - cooling or warming. From the many fires in the
Mediterranean area of partly wet material not only aerosols are emitted, at which
immediately condensation takes place, but in addition biogene substances emerge
H.-J. Bolle
Westrum (1999) point out that the natural regrowth of burned forests in Greece
partially depends on the grazing goats which eat leaves and suppress the recovering
of deciduous trees like Quercus species.
Often in burned areas monocultures of Pinus are re-forested rather then mixed
cultures and the carpet of fallen needles underneath suppresses undergrowths and
degrades soils by acidification.
The burning of agricultural debris as well as the wildfires are an important
source for aerosols and cause a hazy atmospheric boundary layer over large areas.
The burning thus have an impact on the radiative transfer but also an atmospheric
chemistry since with the water vapour, carbon dioxide and aerosols also large
amounts of the BVOes are set free by the fires. These fires are concentrated at the
end of the vegetation period and at the beginning of the rainy period. Some of the
material therefore is washed out and deposited at the surface. Since these are partly
acidic components it contributes to acidify the soils.
5.4 The Role of Aerosols
The aerosol content of the Mediterranean atmosphere varies largely. Few
measurements indicate that the amount of aerosol increased since the fifties at least
in some heavily industrialized areas. Aerosols interact in various ways with the
atmospheric radiative transfer and constitute an important climate factor. Dry
aerosols reduce the solar radiation at the surface and hygroscopic aerosols are
responsible for cloud formation and rain, if the moisture is present. Aerosols
furthermore interact with remote sensing from space. The limi ted knowledge of their
radiative properties and concentrations hampers the correction of satellite data. One
of the great deficits for coping with these different aspects is the lack of an aerosol
climatology for the Mediterranean basin.
Four types of aerosols are of specific importance in the Mediterranean area:
Industrial aerosols, sea-spray aerosols, sand particles, and aerosols ofbiogene origin.
They act in different ways. Hygroscopic salt particles produced by sea spray foster
the condensation as do many of the industrial aerosols. The presence of Saharan
sand particles is an outstanding feature of the Mediterranean atmosphere. Desert
sand particles are not hygroscopic and due to absorption of solar radiation they may
even warm the dusty atmosphere, dissolve clouds, and thus prevent condensation,
a process which sometimes can be observed in satellite images. Their climatic effect
primarily is the backscattering of solar radiation to space and thus the reduction of
the short wave radiant energy which reaches the surface. This counteracts the
greenhouse effect since it causes cooling at the surface. The same effect have
sulphate particles of industrial origin. On the other hand, in the thermal infrared,
they make the atmosphere more opaque which increases the long wave atmospheric
radiation. The ratio of their longwave to shortwave properties determine which of
the effects dominates - cooling or warming. From the many fires in the
Mediterranean area of partly wet material not only aerosols are emitted, at which
immediately condensation takes place, but in addition biogene substances emerge