Aerosols are tiny particles suspended in the atmosphere and that have an impact on our climate as well as on our health. Data provided by various sources is evaluated when a measurement is carried out by ATMOS Aerosol Research: geostationary and LEO-satellites, ground stations of Aeronet and/or targeted in-situ-measurements on a stationary basis or with the help of drone flights.
In order to evaluate the data properly, the so-called GRASP (Generalized Retrieval of Aerosol and Surface Properties) algorithm is used. GRASP is a high-precision aerosol retrieval algorithm that processes properties of aerosol and land surface reflections.
It comprises nearly 50 aerosol and surface parameters, including particle size distribution, spectral index of refraction, degree of sphericity and absorption. The algorithm has been developed to improve characterisation of aerosol properties using spectral, multiangle polarimetric remote observations. GRASP works under various conditions, including bright surfaces like deserts, where reflection overwhelms the signal of aerosols. GRASP is highly versatile and allows input from a variety of satellite and surface measurements.
What are Aerosols? | Video
What is GRASP? | Video
In the atmosphere numerous particles can be found, however, there is usually one prevalent type. A measurement carried out by ATMOS Aerosol Research can identify these particles. They are classified according to their inherent properties based on different criteria.
Aerosols influence the temperature in the atmosphere. Because of this they can have a cooling or warming effect, depending on their type and concentration.
Atmospheric aerosols that originate from the suspension of minerals in the ground are called mineral dust. Even though human activities lead to an increase in dust pollution in the atmosphere, mineral dust is considered to be a natural aerosol. The Sahara is the main source of mineral dust, which subsequently spreads across the Mediterranean and Caribbean Seas to the northern parts of South America, Central America, North America and Europe. It plays a significant role with regard to the supply of nutrients to the Amazon rainforest. The Gobi desert is another source of dust in the atmosphere, which affects East Asia and the western parts of North America.
Aerosol particles that originate from smouldering combustion can be found for a much longer period of time compared to the relatively short duration of flaming fire. Smoke particles of smouldering origin are generally less absorbent than particles stemming from flaming combustion because of their lower content of black carbon.
Fires in boreal woods are characterised by a predominant flaming phase and therefore release significant amounts of black carbon. Due to their high intensity these fires create aerosol particles dominated by smoke. These are generally characterised by high absorption.
Sea salt and water dominate in maritime aerosols above the tropical Pacific Ocean. In that region the aerosol optical thickness, a measure for the optical effective mass of aerosols, is stable at medium level. Above the tropical and subtropical Atlantic the aerosol optical thickness is significantly higher – due to the frequent presence of dust, smoke and urban / industrial aerosols.
Urban aerosols consist of particles of the so-called fine and coarse modes. Based on the differences in the observed properties two types of urban aerosols are usually distinguished: urban clean aerosols are characterised by a fine mode consisting of water and soluble material (e.g. sulphates and ammonium nitrate) which weakly absorb sunlight. Urban polluted aersols have a large number of particles with carbon-containing materials stemming from combustion processes and characterised by high absorption.