Absorption by aerosols

Gerber, H., and E. Hindman, 1982. Light Absorption by Aerosol Particles, Spectrum Press, Hampton, Va. 

The two important atmospheric processes are molecular absorption and molecular and aerosol scattering. Absorption by aerosols, both liquid and particulate, is not thought to be important. 

The problem of the optical characteristics of the aerosols, soot particles included, was discussed at the First International Workshop on Light Absorption by Aerosol Particles (IWLAAP) [24]. The real part, , of the StA complex refractive index in the visible (0.3-0.7 Pm), according to V. Egan [24], varies from 1.665 to 1.775 (w c 2.0-li, for the visible). 

Fraction of light incident upon an aerosol that is removed from the primary beam per unit length by absorption by aerosol particles depends on RH, wavelength A, and complex index of refraction m... 

Amott W. P., MoosmuUer H., Rogers C. F., Jin T. F., and Bruch R. (1999) Photoacoustic spectrometer for measuring light absorption by aerosol instrument description. Atmos. Environ. 33, 2845—2852. 

Fig. 2-10. Upward directed flux Fv, downward directed flux Fn, and total actinic flux FT as a function of altitude in the lower atmosphere. Values are given relative to a solar constant of unity for two wavelengths, 332.5 and 575 nm, and for two zenith angles, 20° and 78°. The calculations of Peterson (1976) took into account Rayleigh scattering, absorption by ozone, and scattering and absorption by aerosol particles.

Figure 3.10 illustrates the schematic diagram of various radiation types contributing to the actinic flux. Thus, for the calculation of F(X), all of the processes, such as absorption by stratospheric ozone, Rayleigh scattering by atmospheric molecules, scattering and absorption by aerosols and clouds, and reflection at the earth s surface have to be considered, and not only the direct radiation from the sun but also the light from all directions reflected and scattered by aerosols must also be accounted for. 

A non-uegligible fraction of the solar radiation incident on the earth is lost by reflection from the top of the atmosphere and tops of clouds back into outer space. For the radiation penetrating the earth s atmosphere, some of the incident energy is lost due to scattering or absorption by air molecules, clouds, dust and aerosols. The radiation that reaches the earth s surface... 

Apart from the economic significance of such loss there are potentially adverse effects on the environment arising from acidification of rain and soil. Ammonia may react with hydroxyl radicals in the atmosphere to produce NOx contributing to the acidification of rain (4). Wet and dry deposition of NH3/NH4+ inevitably contributes to soil acidification through their subsequent nitrification. This effect can be accentuated in woodland by absorption of aerosols containing NH4+ within the canopy followed by transport to the soil in stem flow (5). In more extreme cases, NH3 emission from feedlots, pig and poultry... 

Ehrhardt C, Fiegel J, Fuchs S, Abu-Dahab R, Schaefer UF, Hanes J, Lehr CM (2002) Drug absorption by the respiratory mucosa Cell culture models and particulate drug carriers. J Aerosol Med 15 131-139... 

There are also more limited treatments of scattering. McCartney (1976, Chaps. 4-6) confines his attention to scattering by atmospheric particles. This is also discussed by Twomey (1977, Chaps. 9-10) in his treatise on atmospheric aerosols. In Goody (1964, Chap. 7) there are discussions of absorption by gases and, in less detail, extinction by molecules and by droplets. Parts of books on electromagnetic theory or optics include the theory of scattering by a sphere, most notably Stratton (1941, pp. 563-573) and Born and Wolf (1965, pp. 633-664). The latter also derive the Ewald-Oseen extinction theorem and apply it to reflection and refraction at a plane interface (pp. 98-104). 

Fischer, K., 1970. Measurements of absorption of visible radiation by aerosol particles, Beitr. Phys. Atmos., 43, 244-254. 

---