Solar irradiation/radiation

There are new ideas and experiments on the rTCA cycle. A group from Harvard University studied some reaction steps in the rTCA cycle which were kept going by mineral photochemistry. The authors assumed that solar UV radiation can excite electrons in minerals, and that this energy is sufficient to initiate the corresponding reaction steps. In this photocatalytic process, semiconductor particles were suspended in water in the presence of a zinc sulphide colloid (sphalerite) the experiments were carried out in a 500 mL reaction vessel at 288 K. Irradiation involved a UV immersion lamp (200-410 nm) in the photoreactor. Five reactions out of a total of 11 in the rTCA cycle were chosen to check the hypothesis ... 

Fig. 5.43 The UV part of the sun spectrum, the erythema action spectrum and the biological effective solar irradiance. The biological effective irradiance has been obtained by folding the radiation density of the sun with the erythema action spectrum.

DNA strongly absorbs UV radiation, especially mid-range UVB (290 to 320 nm) radiation. Two major DNA lesions are induced following UV exposure, pyrimidine dimers and 6-4 pyrimidine-pyrimidone photoproducts. Because the action spectrum (induction of a biological activity as a function of wavelength) for erythema closely matches the action spectrum for pyrimidine dimer formation, DNA is believed to be the chromophore for sunburn.6 Pyrimidine dimer formation, or more properly, the failure to adequately repair dimers after solar irradiation is also the primary cause of sunlight-induced skin cancer formation.7-8... 

Franklin LA, Forster RM (1997) The changing irradiance environment consequences for marine macrophyte physiology, productivity and ecology. Eur J Phycol 32 207-232 Frederick JE, Snell HE, Haywood EK (1989) Solar ultraviolet radiation at the earth s surface. Photochem Photobiol 50 443 450... 

The sun s total radiation output is approximately equivalent to that of a blackbody at 10,350°R (5750 K). However, its maximum intensity occurs at a wavelength that corresponds to a temperature of 11,070°R (6150 K) as given hy Wien s displacement law. A figure plotting solar irradiance versus spectral distribution of solar energy is given in Fig. 9. See also Solar Energy. 

Zerefos C.S., Factors influencing the transmission of solar ultraviolet irradiance through the Earth s atmosphere, in Solar Ultraviolet Radiation, Modelling, Measurements and Effects, edited by C.S. Zerefos and A.F. Bais, pp. 133-142, NATO-ASI Series, vol.52, Springer Verlag, 1997. 

The 10 min sums of erythemal solar irradiances measured simultaneously during ten months at two locations in the Czech Republic were analysed. The altitude effect is about 4 to 8% per 1000 m, the radiation amplification factor is about 1.1 and both numbers vary only slightly with solar zenith angle. The statistical model relating erythemal solar irradiance with total column ozone and solar zenith angle was developed. This model and the annual cycles of the mean and variability of total column ozone are used to estimate variability of annual and daily cycles of mean erythemal solar irradiance. 

A Pyrex glass bottle of 50-mL capacity was used as batch reactor. In these flasks 40 mL of water was the total volume. Solar irradiation was simulated by a Hanau Suntest (AMI) lamp. Total radiation measurements were carried out with an YSI corporation power meter. Experiments were performed at room temperature (25°C) reaching up to 32°C during irradiation. 

Solar radiation is a form of thermal radiation having a particular wavelength distribution. Its intensity is strongly dependent on atmospheric conditions, time of year, and the angle of incidence for the sun s rays on the surface of the earth. At the outer limit of the atmosphere the total solar irradiation when the earth is at its mean distance from the sun is 1395 W/m2. This number is called the solar constant and is subject to modification upon collection of more precise experimental data. 

Fig. 3 The solar irradiance from X = 1 nm to X = 0.1 mm and normalized black-body radiation for T = 5770 K. Solar irradiance data are from SOLAR2000 http //www.spacewx.com/ solar spectrum.html for 8 February 2002...

The upper wavelength range in which reaction 9 has been studied is relatively near the lower end of solar UVB radiation, but at present very little information is available on the real environmental role of such a process, if it has any. However, since the occurrence of reaction 9 under UVB irradiation cannot be excluded, Mack and Bolton discussed the need to revisit the reaction pathways proposed for the transformation of organic molecules in the presence of irradiated nitrate and nitrite in the light of the findings concerning the possible formation of HOONO/ONOCT [24], Since new data concerning the transformation reactions of phenol in the presence of N03 + hv, N02 + hv and HOONO are now available, the possible role of peroxynitrous acid in that particular case will be discussed later (Sect. 3.2.3). 

The photochemical effects of solar irradiation on cellulose products have been ascribed to a complex set of reactions in which both the absorption of light and the presence of oxygen, moisture, and impurities are involved (35,51). Solar radiation usually is defined as an electro-... 

From Equation (5), it is clear that the basic parameter that decides the light harvesting ability of the photocatalyst is its band gap. The ideal limiting efficiencies for conversion of solar radiation calculated by Equation (5) as a function of the band-gap wavelength for standard AM 1.5 solar irradiation in a single band-gap device are represented in Figure 9. 

Concentrating collectors are only able to use a limited fraction of fhe diffuse solar radiation. This utilizable fraction can be estimated as the inverse of the concentration ratio of fhe collecfor (1/Cr) (Rabl, 1985). Because of this, parabolic trough photocatalytic reactors, which have a concentration ratio around 15 or higher, miss practically all diffuse radiation. This amounts to losing around half of fhe available UV solar irradiance. 

In addition to the above, the reduction in treatment time with concentration is also an attractive feature of the 2 suns collector, in spite of the fact that it misses aroimd 25% of the available radiation. Due to the abundance of solar irradiation in the test site (Temixco, Morelos, Mexico), it does not appear that sacrificing a part of the UV radiation is such a great concern. However, in depth techno-economic analyses are required to support this assertion. 

Figure 4-5. Wavelength distributions of the sun s photons incident on the earth s atmosphere and its surface. The curve for the solar irradiation on the atmosphere is an idealized one based on Planck s radiation distribution formula (Eq. 4.3a). The spectral distribution and the amount of solar irradiation reaching the earth s surface depend on clouds, other atmospheric conditions, altitude, and the sun s angle in the sky. The pattern indicatedby the lower curve is appropriate at sea level on a clear day with the sun overhead.

Essentially all of the energy for life originates in the form of electromagnetic radiation from the sun. In radiometric units the radiant flux density of solar irradiation (irradiance) perpendicularly incident on the earth s atmosphere—the solar constant — is about 1366 W m-2. The solar constant varies by up to 3.4% from the average due to the earth s elliptical orbit. The value given is for the mean distance between the earth and the sun (the earth is closest to the sun on January 3, at 1.471 x 10s km, and furthest away on July 4, at 1.521 x 108 km). There are additional variations in solar irradiation based on changes in solar activity, such as occur for sun spots, which lead to the 11-year solar cycle (Pap and Frolich, 1999). In Chapter 6 (Section 6.5) we will consider the solar constant in terms of the annual photosynthetic yield and in Chapter 7 (Section 7.1) in terms of the energy balance of a leaf. 

Figure 7-2. Wave number and wavelength distributions for direct solar irradiation, skylight, and radiation emitted by a leaf at 25°C. Wave number (introduced in Problem 4.2) equals the reciprocal of wavelength and thus is proportional to energy (see Eq. 4.2a Ex = hv = hc/Xvac). The areas under the curves indicate the total energy radiated 5direct is 840 W m-2, iSsky is 80 W m-2, and the IR emitted is 860 W m-2.

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