Aerosols are tiny particles suspended in the atmosphere which have an impact on our climate and on humans themselves – watch our video What are Aerosols? With the aerosol app we manage an easy access to aerosol classification and distribution. Catalysts develops the aerosol app in collaboration with LOA.
heating / cooling effect
Aerosols have an impact on the temperature in the atmosphere. As a result they can have a cooling or warming effect, depending on which type they correspond with and in what concentration they occur.
prevalent particle detection
In the atmosphere, there are large numbers of particles, but usually there is only one prevalent type. The aerosol app can identify those particles in many cases. The classification into different types happens due to their intrinsic properties, based on different criteria, described within the app. You are an Expert? We are looking forward to your feedback on our classification of aerosols:
Mineral dust is a term used to indicate atmospheric aerosols originated from the suspension of minerals constituting the soil. Mineral dust is considered as natural aerosol, although human activities also lead to increase of the dust load in the atmosphere. The Sahara is the major source of mineral dust, which subsequently spreads across the Mediterranean and Caribbean seas into northern South America, Central America, North America, and Europe. Additionally, it plays a significant role in the nutrient inflow to the Amazon rainforest. The Gobi Desert is another source of dust in the atmosphere, which affects Eastern Asia and Western North America.
Aerosol particles which form due to smoldering combustion occurring over a much longer period of time relative to the comparatively short lives flaming phase of the crown fires. Smoke particles of smoldering origin generally much less absorbing compare to particles of flaming combustion due to lower content of black carbon.
Aerosol particles that form from high-intensity fires, which are common in boreal forests, and these predominately flaming phase fires likely produce significant amounts of black carbon. Therefore, such smoke dominated particles produced by flaming combustion are generally characterised by high absorption.
Maritime aerosol found over the tropical Pacific Ocean (observations between 20°S and 20°N), still resembles mostly clean background conditions dominated by sea salt and water. The optical thickness is fairly stable with mean value of aerosol optical thickness at 500 nm about 0.07. Average Ångström exponent ranged from 0.3 to 0.7 characterises the wavelength dependence of the optical thickness. Over the tropical to subtropical Atlantic (observations between 7°S and 32°N) the optical thickness is significantly higher (up to 0.2) due to the frequent presence of dust, smoke and urban/industrial aerosol that also may lead to increase of the Ångström exponent values up to about 1.2.
Urban Aerosols are composed by particles of so-called fine and coarse mode. The generally dominant fine mode is comprised by nuclei, Aitken and accumulation mode particles. The nuclei mode (particle diameter < 0.01 µm) are thought to be generated by gas-to-particle conversion processes. The Aitken mode particles (extending from 0.01 to 0.1 µm in diameter) are formed by gas-to-particle conversion as well as by condensation of hot vapors during combustion processes. These particles act as nuclei for the condensation of low-vapor pressure gaseous species, causing them to grow into bigger particles. Particles with diameters between 0.1-1.0 µm are considered as the accumulation mode, representing a region of particle growth mainly due to the condensation of vapors onto existing particles and coagulation of the Aitken mode particles. The particles in this size range can also be introduced directly into the atmosphere through the incomplete combustion of wood, oil, coal, gasoline and other fuels. Because of the nature of their sources, particles in the fine mode are generally contain substantial amounts of organic material as well as soluble inorganics such as ammonium, nitrate and sulphate. The coarse mode particles (particle diameter > 1 µm) can be produced by growth of the fine mode particles and uplift of dust. Due to differences in the observed properties often two types of urban aerosol are differentiated:
- Urban Clean Aerosol is generally dominated by fine mode, composed by water and soluble materials (e.g. sulphates and ammonium nitrates) that are generally weakly absorb the solar light.
- Urban Polluted Aerosol – see below
Urban Polluted Aerosol has pronounced presence of coarse mode containing the particles that include carbonaceous materials generated in combustion processes and characterised by high absorption.
The background aerosol can be divided into two categories: tropospheric aerosol and stratospheric aerosols. The tropospheric background component is characterised by low concentration aerosol of local origin. The important source of particulate in the stratosphere (altitude from 11 to 50 km) is the formation of sulphuric acid droplets by gas-to-particle conversion of SO2 injected into the stratosphere by volcanic eruptions. These sulfuric acid droplets can serve as condensation nuclei to form clouds in the atmosphere. Major volcanic eruptions can result in long-term (several years) increase of the stratospheric particulate concentration by two orders of magnitude. For example, the Mount Pinatubo eruption in 1991 injected 14-20 Tg of SO2 into the stratosphere, causing the aerosol concentration to increase from 2-5 µg/m3 to 20-100 µg/m3.
Are you an expert? We are looking forward to your feedback on our empirical classification of aerosols