Water spectral irradiance

The remaining 19.1% of the energy required to split water has to be supplied for the production step. Figure 4 depicts the terrestrial solar direct normal spectral irradiance distribution computed using SMARTS version 2.9.2 model with input file from ASTM Standard Table G 173-03. ... 

The Sun delivers a spectral irradiance at the Earth s surface at AM 1.0 (air mass), without concentrator, of 1.16 W m nm at 2 = 700 nm [2]. The solid angle represented by the Sun seen from the Earth is Q = 6.8 x 10 steradian. From Eq. (10), one calculates in this case Tr = 5500 K, and from Eq. (12) with T = 298 K one obtains rj = 0.946. If the solar spectrum were that of a black body, all wavelengths would lead to the same values of Jr and Figure 1 shows that this condition is fulfilled only if the receiver is outside the atmosphere. At the Earth s surface, absorption by atmospheric oxygen, ozone, water, and carbon dioxide makes the structured solar irradiance spectrum deviate significantly from the ideal black-body spectrum and requires rR(A) to be calculated for each wavelength. 

The light absorption rate of a given chromophore in a water body depends both on the solar spectral irradiance reaching the water surface and on changes in the spectral irradiance as it penetrates down into the water (20, 21). Light absorption and scattering in the stratosphere and troposphere affect... 

Direct photoreaction (eq 4) is important only for halocarbons (e.g., aromatic compounds) that significantly absorb radiation at wavelengths >295 nm, the cutoff for solar spectral irradiance at the earth s surface. Because saturated chlorinated and fluorinated organic compounds, including methylchloroform and chlorofluorocarbons, absorb solar radiation very weakly, their direct photoreaction is very slow in the sea and in fresh waters. As discussed in a later section, photoreactions of these compounds may be accelerated by sorption and indirect photoreactions in natural waters. Saturated and olefinic polv-brominated and iodinated organic compounds have long absorption tails that extend beyond 295 nm. Direct photoreaction of such compounds in aquatic environments may be significant. 

K. S. Baker, R.C. Smith (1982). Spectral Irradiance penetration in natural waters. In J. Calkins (Ed.), The Role of Solar Ultraviolet Radiation in Marine Ecosystems, NATO Conference Series IV, Marine Sciences (Vol. 7, pp. 233-246). Plenum Press, New York. 

FIGURE 4.9 (a) Solar spectral irradiance at the top of the atmosphere and at sea level. Shaded regions indicate the molecules responsible for absorption. Absorption spectra for (b) molecular oxygen and ozone, (c) water vapor, and (d) the atmosphere, expressed on a scale of 0-1. 

Fig. 1. Hemispherical solar spectral irradiance incident on a 37°-tilted surface facing the equator (air mass 1.5, albedo 0.2, turbidity 0.27, ozone 3.4 mm, precipitable water 14.2 mm). Based on data in Table 1 of ASTM G159-98 2. Courtesy of the American Society for Testing and Materials.

Fluorescent ultraviolet lamps within an apparatus that allows condensation cycles rather than the water spray typical of xenon arc tests have been developed for plastics testing (279). The spectral cutoff wavelength of the lamps used in the apparatus determines the severity of the test. Ultraviolet B (UVB) 313 lamps allow a significant irradiance component below 290 nm, which is normally filtered out by the earth s atmosphere. Ultraviolet A (UVA)... 

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