Optical properties of aerosols

Most widely used space bom measurement for the wildfire studies is MODIS. There are two MODIS s onboard satellites and they cover the Earth s surface every 1-2 days. MODIS gives information on the location of fires and also on the optical properties of aerosol. Optical properties of the smoke particles have also been studied by using the ozone monitoring instrument [32] onboard EOS-Aura satellite. Cloud-aerosol lidar with orthogonal polarization provided the vertical profile of the plume during the smoke episode in 2010 [32], In addition to comparison with ground-based instruments, the data from the space bom instruments has been used in the modeling of smoke plumes (e.g., [10]). 

A fundamental factor required for consideration of the optical properties of aerosols is the particle refractive index m. The refractive index of a material is defined as the ratio of the speed of light in a vacuum to the speed of light in the material. When there is appreciable absorption of radiation in the aerosol particle as well as scattering, it is necessary to express the refractive index of a material as a complex number of the form... 

Zhang Y, Hu X-M, Wang K, Huang J-P, Fast JD, Gustafson Jr. WI, Chu DA, Jang C (2005b) Evaluation of WRF/Chem MADRID with satellite and surface measurements chemical and optical properties of aerosols. Oral presentation at the 2005 AGU Fall Meeting, San Francisco, CA, 5-9 Dec 2005... 

As noted in Section 4.04.2.3, key optical properties of aerosols are represented by the light-scattering coefficient, and light-absorption coefficient, both with reference to the particulate matter. The light-scattering coefficient of an aerosol can be measured by using nephelo-metry (Table 2). The integrating nephelometer (Anderson et al., 1996) exposes an aerosol to... 

Sloane, C. S. (1983) Optical properties of aerosols Comparison of measurements with Model calculation, Atmos. Environ. 17, 409 -19. 

A, A, Kokhanovsky and E, P, Zege, Optical properties of aerosol particles A review of approximate analytical solutions, J. Aerosol Set, 28 1-21, 1997... 

Vallius M, Ruuskanen J, Mirme A et al (2000) Concentration and estimated soot content of PMj, PM2.5 and PMio in a subarctic urban atmosphere. Environ Sci Technol 34 1919-1925 Vrekoussis M, Liakakou E, Kocak M et al (2005) Seasonal variability of optical properties of aerosols in the Eastern Mediterranean. Atmos Environ 39 7083-7094 Waisel Y, Ganor E, Epshtein V et al (2008a) Airborne pollen, spores, and dust across the East Mediterranean Sea. Aerobiology 24 125-131... 

The optical properties of aerosols are responsible for many spectacular atmospheric effects, such as richly colored sunsets, halos around the sun or moon, and rainbows. They also cause the degradation of visibility associated with atmospheric pollution. The interaction of aerosol particles with light forms the basis for an important class of instruments used for measuring aerosol particle size and concentration. Optical measurement methods have the advantages of being extremely sensitive and nearly instantaneous and of not requiring physical contact with the particles. 

Sinclair, D., Optical Properties of Aerosols, in Handbook on Aerosols, USGPO, Washington, DC (1950). 

An important factor in deriving 03 concentrations is the presence of aerosol particles, which also scatter light at 0.6 ixm. Thus, correction for their contribution to extinction at this wavelength must by applied to derive the ozone concentrations. This requires some assumptions regarding aerosol particle properties such as the size distribution, which is not known. It is also commonly assumed that the optical properties of particles do not change with altitude. Such problems introduce uncertainties into the calculation of the particle contribution (e.g., Steele and Turco, 1997a, 1997b Thomason et al., 1997 Fussen, 1998) and hence into the ozone concentrations extracted from such data. 

Patterson, E. M., Optical Properties of the Crustal Aerosol Relation to Chemical and Physical Characteristics, J. Geophys. Res., 86, 3236-3246 (1981). 

Pilinis, C., and X. Li, Particle Shape and Internal Inhomogeneity Effects on the Optical Properties of Tropospheric Aerosols of Relevance to Climate Forcing, J. Geophys. Res., 103, 3789-3800 (1998). 

Atmospheric aerosols usually means the solid and liquid particles in the earth s atmosphere, excluding the solid and liquid water particles in clouds, fog, and rain. Although very tenuous and highly variable, they act as condensation nuclei for cloud droplets, alter the optical properties of clouds, and possibly play a role in the formation of smog and acid rain. And an understanding of their optical properties is needed for many applications ... 

Predicting optical properties of atmospheric aerosols from calculations for homogeneous, spherical particles leaves much to be desired. Mie theory may be a gross oversimplification. In addition, there may not be accurate optical constants for the constituents, even those that are known and they may not all be known. Yet even minor constituents can be major contributors to absorption. 

Marenco F. V. Santacesaria, A. Bais, D. Balis, A. Di Sarra, A. Papayannis and C.S. Zerefos (1997) Optical properties of tropospheric aerosols determined by lidar and spectrophotometric measurements (PAUR campaign), Applied Optics, 36,27, 6875-6886. 

The effect of aerosol on the UV flux reaching the earth s surface is reviewed. Under cloudless conditions UV is scattered or absorbed by aerosol. The net effect depends on the optical properties of the aerosol (scattering or absorbing). In cloudy conditions the UV flux attenuation is more pronounced but depends also on the cloud type. In most instances of clear or cloudy skies an attenuation occurs, with a noteworthy departure the case of partly cloudy sky in a rural area. 

Steele, H.M., and Hamill, P. (1990) Effects of temperature and humidity on the growth and optical properties of sulphuric arid-water droplets in the stratosphere, J. Aerosol Sci, 12,517-528. 

The indirect climatic impact of aerosol at the ABL is determined by numerous interactions between aerosol and the dynamics of the microphysical and optical properties of clouds. The input to the atmosphere of anthropogenic aerosol particles functioning as CCN favors an increase in cloud droplet number density. As mentioned above, the related increase in the optical thickness and albedo of clouds, with their constant water content, was called the first indirect effect , which characterizes the climatic impact of aerosol. 

Brenguier et al. (2003) discussed the results of eight series of aircraft measurements of the microphysical characteristics of marine stratocumulus clouds in a broad range of observation conditions (different physico-chemical properties of aerosol, number density values in the interval 50 cm 3-25 cm-3, etc.)- The unique complex of synchronous observations of the microphysical and radiative characteristics of cloud cover obtained can be used to assess the indirect impact of aerosol on clouds and climate based on analysis of the ratio between the cloud optical thickness and effective radius of cloud droplets. Correlation between these values is usually negative, but in a heavily polluted atmosphere it can be positive. From the observational data obtained during ACE-2, the polluted systems of clouds turned out to be somewhat drier and therefore thinner, resulting in the positive correlation between the indirect impact of aerosol on climate and the effective radius of droplets. 

There are many pitfalls in measuring the properties of aerosols. One of the most critical is sampling of particulate matter without disturbing the aerial suspension. There are some optical devices that make measurements of an aerosol in situ without disturbance. However, most devices requires that a small sample be taken from the gas-particle suspension. Because of inertial forces acting on particles, it can be deduced readily that siphoning part of the fluid... 

The optical effects of aerosols are spectacular. Clouds, haze, and smoke all appear as they do because of the optical properties of the individual particles and the effects of these particles on each other. Few people are not affected by the drama of light scattering and absorption brilliant sunsets inspire, myriad cloud colors excite, and dense, thick fogs disorient. 

Baumer D, Vogel B, Kottmeier Ch (2004) Parameterizing optical properties of soot-containing aerosols. European Aerosol Conf, Budapest, H, September 6-10, 2004, J. Aerosol Science, 35, pp 1195-1196... 

The IWLAAP participants have also undertaken a study of the dependence of the optical properties of StA on the percentage of ammonium sulfate in the particles, as a model of interior mixing of aerosols (Table 1). 

These data, apart from being of purely practical interest, are also important from the viewpoint of understanding the laws of formation of the optical properties of the internally mixed atmospheric aerosol. 

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