Solar attenuation

Photochromic lenses for eyewear serve as variable density optical filters. Other appHcations for photochromic light filters have been proposed including gla2ing appHcations for solar attenuation, variable transmission camera lenses, and shields for protection against the light flash from a nuclear explosion. 

W.G. Sunda, S.A. Huntsman (1990). Effects of sunlight and anthropogenic alterations in atmospheric solar attenuation on manganese redox cycles in surface seawater. In N.V. Blough and R.G. Zepp (Eds), Effects of Solar Ultraviolet Radiation on Biogeochemical Dynamics in Aquatic Environments (pp, 104-107). Technical Report No. WHOI-90-09. Woods Hole Oceanographic Institution. Woods Hole, MA. 

Cinnseleach R., Boschloo G., Rao S.N., Fitzmaurice D. Electrochromic windows based on viologen-modified nanostructured Ti02 films. Sol. Energy Mater. Sol. Cells 1998 55 215-233 Cogan S.F., Plante T.D., Parker M.A., Rauh R.D. Electrochromic solar attenuation in crystaUine and amorphous Li WOs. Sol. Energy Mater. Sol. Cells 1986 14 185-193 Coleman J.P., Lynch A.T., Madhukar P., Wagenknecht J.H. Antimony-doped tin oxide powders Electrochromic materials for printed displays. Sol. Energy Mater. Sol. Cells, 1999 56 375-394 Corr D., Bach U., Fay D., Kinsella M., McAtamney C., O Reilly F., Rao S.N., Stobie N. Coloured electrochromic paper-quality displays based on modified mesoporous electrodes. Solid State Ion. 2003 165 315-321... 

The attenuation of solar radiation has been studied by McCormick and his associates (11, 12) using the Voltz sun photometer, which makes mea-... 

The rate of photolytic transformations in aquatic systems also depends on the intensity and spectral distribution of light in the medium (24). Light intensity decreases exponentially with depth. This fact, known as the Beer-Lambert law, can be stated mathematically as d(Eo)/dZ = -K(Eo), where Eo = photon scalar irradiance (photons/cm2/sec), Z = depth (m), and K = diffuse attenuation coefficient for irradiance (/m). The product of light intensity, chemical absorptivity, and reaction quantum yield, when integrated across the solar spectrum, yields a pseudo-first-order photochemical transformation rate constant. 

In the preceding discussion, we have calculated the attenuation factors for 10Be for three periods, 200, 7 x 103 and 10s years. Of these the 200 and 7000 year periods are well established and have been ascribed to solar cycle variations and earth s magnetic field excursions, respectively. For detailed calculations on the effect of these variations on the production rates of isotopes by cosmic rays reference is made to Castagnoli and Lal, 75.)... 

California has nine solar stations with 11 square miles of mirrors focused on steam drums that drive steam turbines. They can generate 413 megawatts (MW) of electricity which is less than 1% of the state s capacity. Because the sun sets at night and is sometimes attenuated by clouds, the plant production only averaged 0.3% of California s electricity. 

Figure 19.2 Spectral power distribution of UV radiation from a solar simulator (ORIEL) (SSUV) simulated solar zenithal UV (intense solar UVB domain) (DUV) simulated daily UV (attenuated solar UVB domain) (UVA) solar UVA (no UVB).

T0544 National Renewable Energy Laboratory Solar Detoxification of Water T0546 Natural Attenuation—General... 

Outside the atmosphere, the solar flux approximates blackbody emission at 5770 K. However, light absorption or scattering by atmospheric constituents modifies the spectral distribution. The attenuation due to the presence of various naturally occurring atmospheric constituents is shown by the hatched areas in Fig. 3.12. 

Photochemistry of the Polluted Stratosphere. The intensity of solar ladi.i tion reaching the stratosphere is attenuated by oxygen and ozone. Sim < < < s is transparent to radiation of wavelengths above 1800 A, while 03 absi.il, light weakly in the region 1900 to 2100 A [see Figs. VI-12b and 12c. 11,< effective wavelengths of solar radiation for photodissociation are 18(>o n. 2200 and above 2900 A in the stratosphere (843). 

The data calculated from satellite readings of extraterrestrial solar flux may be accurate for cloudless and aerosol free skies. In the case of cloud covered skies the retrieval of aerosol attenuation factor becomes extremely complicated. In the case of cloudless skies, the aerosol attenuation factor q for UV flux at the earth s surface depends on the optical (and chemical properties) of he aerosol, i.e. as to whether the aerosol is absorbing or non absorbing at the wavelengths of interest. This is well depicted in figure 9 below. (Krotkov et al., 1998). 

Figure 9 Aerosol attenuation factor I) (A)= 1- F er (A)/ Fckjr (A) at 325 nm for nonabsorbing (triangles) and absorbing (diamonds) aerosols as a function of the TOMS Lambert-equivallent reflectivity (R-0.05)/0.9 (the true surface reflectivity Rj= 0.05). Solar zenith angle is 50°, satellite zenith angle 32° and azimuth 90°...

Figure 10 Global map of aerosol UV-flux attenuation factor rj= 1-F,er/Fd(air = l-exp -(k/b)AI, estimated from the aerosol index map. The conversion factor k/b= 0.25, was obtained from the clear sky radiative transfer calculations, assuming single layer (dust or smoke) between 2and 4 km and solar zenith angle 30°. The map shows that aersosol absorption can produce very large reduction in UV flux ( 50%) in certain parts of the world (from plate 2 of Krotkov et al. 1998).

Lean, D. 1998. Attenuation of solar radiation in humic waters. In Aquatic Humic Substances (D. O. Hessen, and L. J. Tranvik, Eds.), pp. 109-124. Springer-Verlag, Berlin. 

---