Solar measurement conditions

Atmospheric density decreases disproportionately with altitude. Most of the atmosphere is below an altitude of 57 miles and 20% of it is under 1 mile above sea level. All these attributes of solar energy are constantly changing. A constant value must be chosen for each in order to compare the solar spectral properties of materials. Effective communications about an object s solar properties must be limited to its spectral response under specified solar energy conventions and under standardized measuring conditions. 

Following the same procedure, the kinetic constants have been determined for very different electrochemical conditions. When n-WSe2 electrodes are compared in contact with different redox systems it is, for example, found9 that no PMC peak is measured in the presence of 0.1 M KI, but a clear peak occurs in presence of 0.1 M K4[Fe(CN)6], which is known to be a less efficient electron donor for this electrode in liquid junction solar cells. When K4[Fe(CN)6] is replaced by K3[Fe(CN)6], its oxidized form, a large shoulder is found, indicating that minority carriers cannot react efficiently at the semiconductor/electrolyte junction (Fig. 31). 

This new analytical method determines the rate constant and activation energy of Kevlar s photooxidative processes. The 0.2 atm of oxygen-18-labelled environment in a solar chamber simulates the air-exposure under sunlight conditions. The technique also allows the radial 0-distribution measurement from the fiber surface toward the fiber center. The data from the accelerated experimental conditions in the solar chamber in an 02-atmosphere are differentiated from the usual daylight exposure effects. 

The PV characteristics of the CIGS2 thin-film solar cell on opaque Mo back contact, as measured at the NREL under AM 1.5 conditions, were as follows short-circuit current density sc of 20.88 mA/cm2, open-circuit voltage 1% of 830.5 mV, fill factor FF of 69.13%, and PV conversion efficiency // of 11.99%. 

Figures 7.5 and 7.6 give the measured spectral reflectances and transmittances of fabrics. It is clear from Figure 7.5 that color (6,white 7,black 1,yellow) has a significant effect in reflecting solar irradiance, and also we see why these colors can be discriminated in the visible spectral region of 0.6 pm. However, in the spectral range relevant to fire conditions, color has less of an effect. Also, the reflectance of dirty (5a) or wet (5b) fabrics drop to <0.1. Hence, for practical purposes in fire analyses, where no other information is available, it is reasonable to take the reflectance to be zero, or the absorptivity as equal to 1. This is allowable since only thin fabrics (Figure 7.6) show transmittance levels of 0.2 or less and decrease to near zero after 2 pm.

There are other ways to appreciate the catalytic potency of enzymes in addition to that provided above. A second way to understand the same point is to accurately measure ratios between rates of enzyme-catalyzed reactions and the corresponding uncatalyzed reactions under the same conditions, a refinement of the qualitative argument just made. These ratios are frequently not easy to obtain since the rates of the uncatalyzed reactions may be so slow as to make them exceedingly difficult to measure. Nonetheless, a number of these ratios are known and they typically vary between abont 10 (one thousand) and 10 (one quadrillion), truly enormous values. To help understand just how large 10 is, consider a chemical reaction begun at the time of the creation of our solar system whose progress would be barely detectable at the present day. That same reaction would be nearly complete in 1 minute if catalyzed IQi -fold. 

However, tropospheric ozone formed as an air pollutant by VOC-NOx chemistry discussed throughout this book can also impact solar radiation reaching the earth s surface. For example, Frederick et al. (1993) reported that measurements of broadband UV in Chicago had a marginally significant negative correlation to surface 03 concentrations under clear-sky conditions. 

The use of the sun or moon as the light source allows one to measure the total column abundance, i.e., the concentration integrated through a column in the atmosphere. This approach has been used for a number of years (e.g., see Noxon (1975) for NOz measurements) and provided the first measurements of the nitrate radical in the atmosphere (Noxon et al., 1978). As discussed later in this chapter, such measurements made as a function of solar zenith angle also provide information on the vertical distributions of absorbing species. Cloud-free conditions are usually used for such measurements as discussed by Erie et al. (1995), the presence of tropospheric clouds can dramatically increase the effective path length (by an order of... 

Crowley et al. (1994) have measured the absorption cross sections of CH3OCl and calculate a lifetime with respect to photolysis under stratospheric conditions of 4 h at a solar zenith angle of 80°. The rate of the heterogeneous reaction (38) is not known. 

A similar conclusion is reached using direct measurements of solar fluxes at the top of the atmosphere (TOA) and at surface sites under clear compared to cloudy conditions (e.g., Cess et al., 1995, 1996b Evans et al., 1995). Figure 14.51a shows the absorptance, defined as the fraction of the down-... 

A third way in which thermodynamics can be used is to invert the measured major, minor, and trace element compositions of coexisting minerals to estimate the temperature, pressure, and oxidation state under which they formed. Valid results can only be obtained if the system was truly in equilibrium at the inferred conditions and the minerals did not subsequently change composition. Nevertheless, this is a powerful way to infer the formation conditions of various solar-system materials. 

---