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5.3 Dry vs. Wet Deposition
For several decades, it has been clear that humanity, in addition to extraordinary
successes in many areas of science and technology, is facing environmental threats.
Of particular concern are anthropogenic emissions of pollutants into the atmosphere
in which complex chemical reactions and dynamic processes take place. Substances
emitted into the atmosphere are subject to certain transformation processes over
time, with the formation of new compounds that are deposited on the earth’s surface
together with the originally emitted substances. This deposition takes place without
the participation of water molecules (dry deposition) or with the participation of
water molecules (wet deposition). This leads, in addition to the phenomenon of
cleaning the atmosphere, to certain problems in the environment such as acidification of soil and water systems and damage to biological materials, endangering
human health.
The theoretical processes of dry and wet deposition are very complex. However,
atmospheric pathways and the characteristics of standard and non-standard pollutants are much better described for aerosols than for gaseous substances, for both
wet and dry deposition. Wet deposition refers to acid rain, fog, and snow. All these
acidic precipitations outside and through the ground affect plants and animals. The
strength of this influence depends on a number of factors, the degree of acidity of
the water, chemical and receiving capacity of the soil, and the type of trees, fish, and
other organisms in water (Ajmone-Marsan et al. 2008). Dry deposition refers to acid
gases and particles. About half of the acidity in the atmosphere falls to earth in the
form of dry deposition. The wind causes acid particles and gases on buildings, cars,
houses, and trees. Dry deposited gases and particles can also be washed away by
rain, making the water even more acidic. Dry deposition refers to gases and particles, is independent of atmospheric precipitation, and is regulated by the concentration of pollutants in the air and transport through the boundary layer, the chemical
and the physical nature of the depositional species, and the efficiency of the surface
that accepts or absorbs the deposited material. It is part of the total exchange of matter between the atmosphere and the earth’s surface, all the more so because the
deposited gases are sometimes reversibly absorbed so that, under certain conditions,
they can be re-emitted into the atmosphere (White 2013; Keller et al. 2015). Direct
measurement of dry deposition is complex and very rarely performed in the world
and is estimated by mathematical modelling (Bourennane et al. 2010).
Dry and wet deposition of pollutants in the gaseous state and particles take place
in different ways. The basic characteristics of dry deposition are that the vertical
concentration gradient pushes the molecules toward the soil, thus enabling their
adsorption in the first layers of the soil, or they are retained in the layers of air that
move laminarly in their direct contact with the soil or chemically react with molecules that are on the ground (Gjengedal and Steinnes 1990).
For wet gas deposition, it is characteristic that pollutants reach the ground by
washing with snow or rain. These compounds primarily reach the clouds where
chemical reactions take place, followed by leaching in the form of droplets and
B. Balabanova et al.
5.3 Dry vs. Wet Deposition
For several decades, it has been clear that humanity, in addition to extraordinary
successes in many areas of science and technology, is facing environmental threats.
Of particular concern are anthropogenic emissions of pollutants into the atmosphere
in which complex chemical reactions and dynamic processes take place. Substances
emitted into the atmosphere are subject to certain transformation processes over
time, with the formation of new compounds that are deposited on the earth’s surface
together with the originally emitted substances. This deposition takes place without
the participation of water molecules (dry deposition) or with the participation of
water molecules (wet deposition). This leads, in addition to the phenomenon of
cleaning the atmosphere, to certain problems in the environment such as acidification of soil and water systems and damage to biological materials, endangering
human health.
The theoretical processes of dry and wet deposition are very complex. However,
atmospheric pathways and the characteristics of standard and non-standard pollutants are much better described for aerosols than for gaseous substances, for both
wet and dry deposition. Wet deposition refers to acid rain, fog, and snow. All these
acidic precipitations outside and through the ground affect plants and animals. The
strength of this influence depends on a number of factors, the degree of acidity of
the water, chemical and receiving capacity of the soil, and the type of trees, fish, and
other organisms in water (Ajmone-Marsan et al. 2008). Dry deposition refers to acid
gases and particles. About half of the acidity in the atmosphere falls to earth in the
form of dry deposition. The wind causes acid particles and gases on buildings, cars,
houses, and trees. Dry deposited gases and particles can also be washed away by
rain, making the water even more acidic. Dry deposition refers to gases and particles, is independent of atmospheric precipitation, and is regulated by the concentration of pollutants in the air and transport through the boundary layer, the chemical
and the physical nature of the depositional species, and the efficiency of the surface
that accepts or absorbs the deposited material. It is part of the total exchange of matter between the atmosphere and the earth’s surface, all the more so because the
deposited gases are sometimes reversibly absorbed so that, under certain conditions,
they can be re-emitted into the atmosphere (White 2013; Keller et al. 2015). Direct
measurement of dry deposition is complex and very rarely performed in the world
and is estimated by mathematical modelling (Bourennane et al. 2010).
Dry and wet deposition of pollutants in the gaseous state and particles take place
in different ways. The basic characteristics of dry deposition are that the vertical
concentration gradient pushes the molecules toward the soil, thus enabling their
adsorption in the first layers of the soil, or they are retained in the layers of air that
move laminarly in their direct contact with the soil or chemically react with molecules that are on the ground (Gjengedal and Steinnes 1990).
For wet gas deposition, it is characteristic that pollutants reach the ground by
washing with snow or rain. These compounds primarily reach the clouds where
chemical reactions take place, followed by leaching in the form of droplets and
B. Balabanova et al.