Aerosols In The Atmosphere

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Aerosols are ever-present and highly-varying constituents of our atmosphere. They play roles in many physical and chemical processes that shape the composition of the atmosphere and thereby affect cloud formation, visibility, and air quality. They interact both directly and indirectly with radiation and thus affect the amount of radiative energy reaching the surface and reflected to space. The shortwave part of the radiative energy at the surface (insolation) is an important component of the surface energy budget, and a necessary input to models of land-surface processes.
To describe the interaction of the earth's atmosphere with solar radiation, the atmosphere's composition must be understood. The atmosphere is composed of a group of nearly
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Natural background aerosols are present in the absence of human activity, while urban aerosols are dominated by anthropogenic sources. In both cases, the primary particles are continuously emitted into the atmosphere, while the secondary ones are formed via oxidation, photolysis and mixing processes. Aerosols are ubiquitous in the air and are often observable as dust, smoke and haze (see Figure 1.1). On a global basis, aerosol mass derives predominantly from natural sources, mainly dust and sea salt. However, anthropogenic aerosols, arising primarily from a variety of combustion sources, can dominate in, and downwind of, highly populated and industrialized regions and over areas of intense biomass burning. Atmospheric aerosols might affect the global climatic system in many ways, that is, by attenuating the solar radiation reaching the ground, by modifying the solar spectrum, by re-distributing the earth-atmosphere energy budget and by influencing cloud microphysics and even the hydrological cycle (IPCC, 2007). Although the optical properties of aerosols are well known, large uncertainties still occur about aerosol-climate interaction due to the variety of aerosol types, their changing optical and physico-chemical properties, the influence of dynamic and synoptic scale meteorology and the mixing (internal and external) processes in the…show more content…
Anthropogenic aerosols are emitted from densely populated and industrialized regions over the globe due to anthropogenic activities and having the greatest climate effect. These are short-lived and mostly fine particles (size <1μm). The main chemical components of anthropogenic aerosols are sulfate, nitrate, organic and inorganic carbonaceous compounds produced by several physical and chemical processes such as gas-to-particle conversion, biomass burning and fossil fuel burning. A substantial fraction of the organic aerosols is water soluble and constitute the efficient Cloud Condensation Nuclei (CCN) which is the important sink for organic aerosols. The marine aerosols are composed of both natural and anthropogenic constituents such as liquid sea water drops, dry sea-salt particles, dust and minerals transported from continental origin and from volcanoes, biological particles (bacteria, viruses), sulfate, nitrates, ship exhaust emissions, soot. The marine aerosols can be generated by several processes such as gas-to-particle conversion, nucleation, condensation and their size ranges from nanometers to millimeter. After emission in the atmosphere sea-salt particles can be internally and externally mixed with other aerosols. Sulfate particles are produced by the aqueous phase reaction within cloud droplets by oxidation of 〖SO〗_2 via gaseous phase

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