Aerosol light-scattering

FIGURE 3 17 Increase in aerosol light-scattering efficiency as a result of aerosol growth. Compare with Figures 3-24 and 3-26. Reprinted with permission from O Brien et al. 

The effect of water on aerosol light scattering is sometimes expressed as the hygroscopic growth factor,... 

Sloane, C. S., Effect of Composition on Aerosol Light Scattering Efficiencies, Atmos. Environ., 20, 1025-1037 (1986). 

Li, X., H. Mating, D. Savoie, K. Voss, and J. M. Prospero, "Dominance of Mineral Dust in Aerosol Light-Scattering in the North Atlantic Trade Winds, Nature, 380, 416-419 (1996). 

Thus, it is important to differentiate between the perturbation effects caused on the atmosphere by light-induced heterogeneous processes on aerosols from those caused by photochemical gas-phase reactions induced or inhibited by aerosol light scattering. In the following subsections several examples of the former type will be discussed. The enhancement of homogeneous photolysis rates and the problem of ozone depletion will not be discussed, as they are outside the scope of the present chapter. 

Hegg D. A., Covert D. S., Crahan K., and Jonssen H. (2002) The dependence of aerosol light-scattering on RH over the Pacific Ocean. Geophys. Res. Lett. 29, doi 10.1029/ 2001GL014495. 

Li X., Mating H., Savoie D., Voss K., and Prospero J. M. (1996) Dominance of mineral dust in aerosol light-scattering in the North Atlantic trade winds. Nature 380, 416-419. 

Aerosol light scattering plays a major role in the design of aerosol meusuretncnt systems (discussed in the next chapter) and radiation transfer through the atmosphere. There are also technological applications in combustion and production of powdered material.s. This chapter provides an introduction to the subject. 

The integrating nephelometer provides information on total aerosol light scattering. Show how the characteristics of the instrument would appear within the framework of Table 6.3. 

Suspended particles are the most important factor in visibility reduction. In most instances, the visual quality of air is controlled by partide scattering and is characterized by the extinction coeffident The size of particles plays a crucial role in their interaction with light. Other factors are the refractive index and shape of the particles, although their effect is harder to measure and is less well understood. If we could establish these properties, we could calculate the amount of light scattering and absorption. Alternatively, the extinction coeffident associated with an aerosol can be measured directly. 

Figure 7-2 shows the vertical profiles of temperature, dew point, light scattering (a measure of aerosol concentration) and the concentrations of O3 and SO2. Here we see that up to about 1.5 km, the temperature, dew point, light scattering... 

One of the newest particle sizing techniques is light scattering. This technique is used to measure particle size distribution, colloid behavior, particle size growth, aerosol research, clean room monitoring, and pollution monitoring. 

In addition to ELS, charged aerosol (CA) or corona detector has more recently been introduced as a very promising HPLC detection system [105] while the sensitivity of the two systems is quite close, CA detector offers the advantage of a nearly linear response factor, particularly crucial for the assessment of enantiomeric purities, whereas ELS provides a nonlinear response at very low or high levels of analytes, resulting from several light scattering mechanisms and particle size distribution. 

Methods for analysis of the particle size distribution in the aerosol cloud include techniques such as time of flight measurement (TOE), inertial impaction and laser diffraction. Dynamic light scattering (photon correlation spectroscopy) is confined to particles (in suspension) in the submicron range. In addition to the size distribution, the particle velocity distribution can be measured with the Phase Doppler technique. 

Evaporative light scattering is gaining popularity due to its ability to detect analytes on a nonse-lective basis. Basically, this detector works by nebulizing the column effluent, forming an aerosol that is further converted into a droplet cloud for detection by light scattering. This type of detector has been applied to studies of small molecule combinatorial libraries [13,14], carbohydrates [15], and lipids [16,17]. 

FIGURE 7.13 Schematic of an evaporative light scattering detector. The three stages are nebulization, in which column effluent is aerosolized evaporation, in which the mobile phase is vaporized and optical detection, in which the light scattering of the residual solute particles is recorded. Some detectors also include an obstacle in the flow path for droplet discrimination, which leads to a more homogenous distribution of droplet sizes. 

Chemical Species Contributions to Light Scattering by Aerosols at a Remote Arid Site... 

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