Deposition (aerosol physics)

Under the atmospheric deposition fluxes from the atmosphere to be understood on the earth's surface, that is, the discharge and the deposition of dissolved and particle -bound and gaseous substances in the air on surfaces ( acceptors ) biotic or abiotic systems. Biotic acceptors are the aboveground shoot parts of plants, especially the leaves and needles. Abiotic acceptors of soil, surface water, snow cover or buildings (roofs, roads, etc.) to be.

Deposition principles

Atmospheric deposition is a complex, existing mechanisms of many individual process. Larger particles and droplets follow the gravity and sediment. Smaller particles are floating with the turbulence of the air currents deposited on surfaces ( impaction ). Gases are released to moist surfaces or adsorbed from dry surfaces.

Dry atmospheric deposition is the discharge of substances by solid particles and small liquid particles ( fog and cloud droplets ) and gases from the atmosphere, including its filing on Akzeptoroberflächen. The operation of the discharge and the storage of materials by small liquid particles ( droplets) is also referred to separately as wet atmospheric deposition. Wet atmospheric deposition is the discharge of dissolved and undissolved ( of particles adhering ) substances obtained by aqueous precipitation such as rain, snow and hail.

A special feature of wet deposition, the Interzeptionsdeposition dar. This is the sediment load, with the dripping of plants precipitation ( in trees: Kronentraufwasser ) reaches the ground. Above-ground parts of plants, especially leaves and needles in forests, also in dry periods or during fog events represent a significant Akzeptoroberfläche ( Auskämmeffekt, fog eaves). When precipitation events, the previously dry deposited and meanwhile partially metabolized substances can be washed off. The wet deposition rates on the floor are characterized in forests, particularly in the non- winter bald coniferous forests, usually increased significantly compared to the field.

Global differences

The discharge of substances from the atmosphere by deposition is not completely irreversible process. A portion of the deposited amount of substance can evaporate back into the atmosphere (remission ). Because the Reemissionrate in warm climatic regions is higher than in cold and also decreases the microbiological activity with temperature, it comes with time to an accumulation of long-lived re-emitted substances in the polar regions ( grasshopper effect).

Measurement of deposition rates

The rate of the deposition with deposition collectors, which are in principle open to the top pots or funnel with a collection vessel. For the measurement of the total deposition of the collecting unit is open during the entire collection period through to the atmosphere (bulk collector ). For the separate determination of wet and dry deposition collectors possess a sensor for detecting precipitation events, the automatic opening and closing a shutter over the collecting unit controls (Wet -only collectors or Dry -only collectors ).

From collecting area, rainfall and concentration, the deposition rate can be calculated. This is the per unit time and unit area deposited amount of substance. Customary units ( milli-, micro - ) grams per square meter per day or ( kilo ) grams per hectare per year.

About the deposition of substantial amounts of substances from the atmosphere to be entered on and in the soil. These also include air pollutants. For certain pollutants (eg POP), the deposition is even the only cause of their ubiquitous distribution in soils. The measurement, knowledge and reduction of the deposition rate is therefore an important part of environmental protection, especially soil conservation and forestry sciences.

• Conservation
• Ecosystem Research