Informations et ressources scientifiques
sur le développement des zones arides et semi-arides

Titre  : Studies aerosol properties using ground based measurements at semi arid region Anantapur

Auteur : Shaik, Mahammad Arafath

Université de soutenance  : Sri Krishnadevaraya University

Grade : Doctor of Philosophy (PhD) 2014

Préface partielle
Atmospheric aerosols are fine solid or liquid particles suspended in the atmosphere with sizes ranging from 10-3 to 102 µm. These particles are not distributed uniformly in the atmosphere. This results from the non-uniform sources and sinks of these particles. It is estimated that approximately 80% of the total aerosol particle mass is contained within the lowest one kilometer of the troposphere. Aerosols originate from different sources : sea-salt from oceans, mineral dust from arid and semi-arid locations, sulfate and nitrate from both natural and anthropogenic sources and organic and carbonaceous aerosols from biomass burning and industrial combustion. Aerosol particles are either emitted directly to the atmosphere (primary aerosols) or produced in the atmosphere from precursor gases (secondary aerosols). A series of epidemiologic studies has clearly shown the causative interconnection between particles and health effects ; frequency rates of chronic obstructive respiratory diseases seem to be increasing. Many studies have generally accepted that the ability for particles to cause health effects is dependent on their size. In spite of the fact that particles up to 100 µm enter the body through breathing, only very small particles, below 5 µm aerodynamic diameter can reach deep into the lung and these very small particles have the main potential for causing health effects. However, there are significant uncertainties in the quantification of the impact of atmospheric aerosols on climate because of a lack of knowledge about their sources, composition, properties, and mechanism of formation. Aerosols play an important role in the global climate balance, and therefore ii they could be important in climate change. Aerosols force climate in two ways (1) Direct radiative forcing, mainly by the scattering and absorption processes depending upon their size distribution, refractive index and total atmospheric loading resulting in the attenuation (or extinction) of solar radiation reaching the Earth’s surface. (2) Indirect radiative forcing, mainly by effects of aerosols on cloud properties (A minor indirect effect involves the heterogeneous chemistry of greenhouse gases : these gases may react at the surface of an aerosol and therefore change radiative properties). On balance, aerosol particles tend to scatter energy back to space and cool the planet. Some types of particles, however, absorb solar radiation and can contribute to local warming of the atmosphere. An example of light absorbing particles is carbon soot generated from combustion processes or forest fires. Because aerosols have much shorter lifetimes and more varied distributions than greenhouse gases, the net effect on global climate is hard to predict. This tends to offset the warming associated with greenhouse gases

Mots clés : aerosol properties using gorund based measurements

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