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Atmospheric aerosol is a suspension of liquid and solid particles, with radii varying from a few run to larger than 100μm, in air. The particles can be directly emitted into the atmosphere (e.g., sea spray aerosol, dust, biomass or fossil fuel burning aerosol, volcanic ash, primary organic aerosol) or produced from precursor gases (e.g., sulfates, nitrates, ammonium salts, secondary organic aerosol)...
Tropospheric aerosols significantly influence global climate, by changing the radiative energy balance as well as the hydrological cycle (e.g., IPCC [2007]). Also known as suspended airborne particles, or particulate matter (PM), aerosols are a component of smog and air pollution (e.g., USEPA [2003], [2002] and [1997]) and a regulated criteria air pollutant (e.g., http://www.epa.gov/oar/particlepollution/naaqs-rev2006...
Atmospheric aerosols interact with sunlight by scattering and absorbing radiation. By changing the irradiance at the Earth surface, modifying cloud fractional cover and microphysical properties and by a number of other mechanisms, they affect the energy balance, hydrological cycle, and planetary climate [IPCC, 2007]. In many world regions there is a growing impact of aerosols on air quality and human...
The retrieval of aerosol characteristics over land from satellite data has been a challenge up to now. Currently, several well known techniques for retrieving aerosol optical thickness (AOT) have been developed for satellite instruments including MODIS (Kaufman et al., 1997; Remer et al., 2005), MERIS (Santer et al., 1999, 2000), POLDER (Deuze et al, 2001), and MISR (Martonchik et al., 2002). While...
Aerosols play an important role in climate and air quality. They have a direct effect on climate by scattering and/or absorbing the incoming solar radiation [Haywood and Boucher, 2000]. Reflection of solar radiation increases the atmospheric albedo, causing a negative radiative effect and therefore cooling of the atmosphere. On local scales absorbing aerosols can cause net positive radiative forcing...
Atmospheric aerosol particles play a critical role in the Earth’s radiation budget, yet the global radiative forcing by aerosols is widely recognized as a major uncertainty in our understanding of the climate [IPCC, 2007]. The radiative characteristics of aerosol particles are determined by their shape, size, total amount and chemical composition [Kaufman et al., 1997a]. Overall though, aerosols have...
This chapter describes an optimal estimation retrieval scheme for the derivation of the properties of atmospheric aerosol from top-of-atmosphere (TOA) radiances measured by satellite-borne visible-IR radiometers. The algorithm makes up part of the Oxford-RAL Aerosol and Cloud (ORAC) retrieval scheme (the other part of the algorithm performs cloud retrievals and is described in detail elsewhere [by...
Air pollution by solid and liquid aerosol particles suspended in the air is one of the major concerns in developed countries because of potential health impact of increasing numbers of nano-particles in particular from diesel engines (see, e.g., [2002] and [2004]), as well as in developing countries with their high particle concentrations in the air. Furthermore, windblown dust can also act as carrier...
Global and regional mapping of aerosol properties, including column amount, particle type and effective size, is of great interest for environmental and climate studies. Increased aerosol production results in decreased insolation (a direct aerosol effect), mitigating the rise in global surface air temperature caused by enhanced concentrations of greenhouse gases, though on different spatial and temporal...
Writing from the S.S. Narkunda, near Aden, [1921] that using a Nicol prism ‘serves to cut off a great deal of the blue atmospheric “haze” which usually envelops a distant view, and mostly consists of polarized light. ’ Although the reason for the color and polarization of the sky had been explained some time before by [1871], later Lord Rayleigh, and the neutral points, where the polarization of the...
Passive spaceborne imagers observe radiation that has interacted both with the atmosphere and the surface. Interactions with the atmosphere include gaseous absorption and scattering by molecules and particulate matter or aerosols. Their characterization from remote sensing observations relies essentially on their capacity to modify differently the amount of radiation observed as a function of the...
Aerosol remote sensing from space is predominantly based on sensor data of reflected sunlight in solar spectral regions, where the attenuation by trace-gases can be neglected or easily accounted for. But even at these spectral regions retrievals of aerosol properties are by no means a simple task, as explained in the previous chapters of this book. This is mostly due to the following major reasons:...
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