Solar Light Intensity Research Articles

Experimental study of a hybrid photocatalytic hydrogen production reactor for Cu–Cl cycle

In this study, we perform experimental investigations of a novel hybrid photocatalytic hydrogen production reactor for a Cu–Cl cycle. The effects of different operating conditions, such as solar light intensity, mass of zinc sulfide and mass of Cu–Cl on rate of hydrogen production are studied. The experimental results show that the photocatalytic hydrogen production rate increases from 0.21 to 0.50 μg/s with an increase in solar light intensity, mass of CuCl and mass of ZnS from 400 to 500 W/m2, 5–10 g and 2–4 g, respectively. It is also observed that increasing the solar light intensity and the mass of ZnS from 400 to 500 W/m2 and 2–4 g, respectively results in increase in hydrogen production rate from 0.28 to 0.48 μg/s. The experimental results further show that replacing the electrolyzer component of Cu–Cl with the studied hybrid photocatalytic reactor can help in making the Cu–Cl cycle more environmentally benign.

Enhanced Solar Photocatalytic Degradation of Phenol with Coupled Graphene-Based Titanium Dioxide and Zinc Oxide

In this study, graphene-based titanium dioxide and zinc oxide composites (TiO2-G, ZnO-G) were synthesized using a hydrothermal process. Materials were characterized using X-ray diffraction, X-ray photoelectron spectroscopy, Raman spectroscopy, UV–vis spectroscopy, scanning electron microscopy, and transmission electron microscopy. Photocatalytic activity of the composite materials under simulated solar light was studied using phenol as a model compound. A ca. 30% improvement on the degradation performance by the TiO2-G composite (and ZnO-G) was observed when reaction rate constants were compared with TiO2 (and ZnO) only. This demonstrates the positive effect of graphene on suppressing charge recombination and extending the light absorption range. Further improvement on the photocatalytic degradation rate of phenol was obtained by coupling the two composites, ZnO-G and TiO2-G. This is attributed to more efficient charge separation and longer lifetime of the charge carriers, which eventually enhances the photocatalytic activity. The optimum stoichiometric amount of each component was obtained experimentally. Systematic parametric studies were also performed to study the effect of catalyst loading, initial phenol concentration, solution pH, and solar light intensity. Complete solar degradation of 40 ppm phenol was achieved within 60 min while using the coupled ZnO-G/TiO2-G photocatalysts at the optimum conditions.

EFFECT OF COVERING MATERIAL AND SHADING ON INTERIOR LIGHT INTENSITY IN POLY-GREENHOUSES

The objective of this research was to examine the influence of two different poly-greenhouse covering material types and their properties on the interior light intensity to choose the proper one for covering under Fayoum depression climatic conditions. Measurements of global solar radiation (GSR) and light intensity were made inside and outside six poly-greenhouse-covered prototype structures (Quonset-style). Each prototype structure was 1.0 m length, 1.0 m width and 0.8 m height. Two small doors in the narrow sides of each prototype were kept open during the day-light for natural ventilation. Results showed that the average transmittance in GSR of both new white polyethylene films and new black screen shade net sheets were 74.05% and 55.45%, respectively. Exposure the poly-greenhouse cover to the climatic conditions reduced its transmittance to global solar radiation (GSR). The relative losses of GSR transmittance were 13.96 % and 17.64 % for both old-cleaned and old-dirty polyethylene films, respectively, as compared with the new polyethylene film (74.05%). The average losses of GSR transmittance were 12.93% and 19.42% for both old-cleaned and old-dirty black screen shade net, respectively, as compared with the new black screen shade net cover (55.45%). The new white polyethylene films and new black screen shade net sheets reduced the interior light intensity of the prototypes by an average of 18.3% and 68.4% as compared with the average exterior light intensity, respectively. In addition, old-cleaned and old-dirty polyethylene films reduced the interior light intensity by an average of 20.8% and 34.8% as compared with the identical new white polyethylene film, respectively. While, old-cleaned and old-dirty black screen shade net reduced the interior light intensity by an average of 27.3% and 39.9 % as compared with the identical new black screen shade net, respectively.

Solar photocatalysis: A green technology for E. coli contaminated water disinfection. Effect of concentration and different types of suspended catalyst

Photocatalytic and photolytic disinfection of Escherichia coli in water was studied under natural sunlight using different types of photocatalyst (TiO2 P-25, PC500, Ruana and Bi2WO6) at different concentrations. The solar photo-inactivation yielded complete inactivation results, which varied with the solar light intensity. Meanwhile, dark control samples in the lab (temperature constant at 25 °C) remained at constant concentration and dark samples outside laboratory showed a decrease due to the mild solar heating occurred during the experiments. The adding of any kind of photo-catalyst to the water accelerated the bactericidal action of solar irradiation and led to complete disinfection (until detection limit). The photocatalytic disinfection efficiency was not enhanced by the increase of catalyst concentration above 0.5 g/L for P-25, PC500 and Bi2WO6, where about 106 CFU/mL were completely inactivated within 5 min, 30 min and more than 150 min of solar exposure under clear sky, respectively. An increase of the concentration to 1 g/L slightly decreased the total inactivation time. Rutile (Ruana) catalyst behaves differently, optimal concentration was lower than for the other titania materials; agglomeration of particles occurred as the concentration of catalyst increases. Durability of photocatalytic treatment and chemicals analyses of inorganic anions and cations have also been investigated.

Solar photocatalytic treatment of phenolic wastewaters: influence of chlorides, sulphates, aeration, liquid volume and solar light intensity

The solar photocatalytic treatment of phenolic wastewater over TiO2 suspensions was investigated. The study focused on the effect of various operating parameters on the treatment efficiency including chlorides (50–200 mg/L), sulphates (50–200 mg/L), aeration (pre-aeration, with and without aeration), liquid volume (0.25–1.5 L) and solar light intensity (throughout the year). The presence of chloride and sulphate ions decreased the degradation rate of phenol due to a decrease in the adsorption of the pollutant and act as hydroxyl ion scavengers. It was observed that the phenol removal efficiency was 30, 85 and 77% for pre-aeration, with and without aeration, respectively. The phenol removal efficiency was 99, 94 and 79% and 46% for wastewater volume of 0.25, 0.50, 1.0 and 1.5 L, respectively. It was observed that as the volume of wastewater was increased, the phenol removal was found to decrease. The phenol removal efficiency reached its maximum of 95% at maximum UV light intensity of 32 W/m2 and the minimum phenol removal efficiency of 59% at minimum UV light intensity of 20 W/m2.

Performance assessment of solar-based integrated Cu–Cl systems for hydrogen production

The present study analyzes two integrated systems for hydrogen production, namely, (a) integrated solar heliostat, Cu–Cl cycle and Kalina cycle system and (b) integrated solar heliostat, Cu–Cl cycle, Kalina cycle and electrolyzer system. The systems operating parameters, such as, solar radiation intensity, mass fraction of hydrochloric acid and ambient temperature are varied to investigate their effects on hydrogen production rate by both systems, amount of hot water required by the Cu–Cl cycle, amount of water required at state cc[1] and energy and exergy efficiencies of the systems. A comparative study is also carried out to compare the effects of operating parameters on the hydrogen production rate and energy and exergy efficiencies of both the systems. The results show that the system 2 produces 297.7L/s of hydrogen as compared to 289.4L/s produced by the system 1 at a solar light intensity of 1200W/m2. It is also found that the system 1 performs 2.15% and 3.36% better than the system 2 from energy and exergy perspectives, respectively when solar light intensity is varied. From energy and exergy perspectives, the system 1 performs 1.92% and 2.91% better than the system 2, respectively with variation in the mass fraction of hydrochloric acid. The results show that energy efficiency is not affected by the increase of ambient temperature while the corresponding exergy efficiency increases considerably.

Sequential deposition as a route to high-performance perovskite-sensitized solar cells

Following pioneering work, solution-processable organic-inorganic hybrid perovskites-such as CH3NH3PbX3 (X = Cl, Br, I)-have attracted attention as light-harvesting materials for mesoscopic solar cells. So far, the perovskite pigment has been deposited in a single step onto mesoporous metal oxide films using a mixture of PbX2 and CH3NH3X in a common solvent. However, the uncontrolled precipitation of the perovskite produces large morphological variations, resulting in a wide spread of photovoltaic performance in the resulting devices, which hampers the prospects for practical applications. Here we describe a sequential deposition method for the formation of the perovskite pigment within the porous metal oxide film. PbI2 is first introduced from solution into a nanoporous titanium dioxide film and subsequently transformed into the perovskite by exposing it to a solution of CH3NH3I. We find that the conversion occurs within the nanoporous host as soon as the two components come into contact, permitting much better control over the perovskite morphology than is possible with the previously employed route. Using this technique for the fabrication of solid-state mesoscopic solar cells greatly increases the reproducibility of their performance and allows us to achieve a power conversion efficiency of approximately 15 per cent (measured under standard AM1.5G test conditions on solar zenith angle, solar light intensity and cell temperature). This two-step method should provide new opportunities for the fabrication of solution-processed photovoltaic cells with unprecedented power conversion efficiencies and high stability equal to or even greater than those of today's best thin-film photovoltaic devices.

Photophoretic interaction of aerosol particles and its effect on coagulation in rarefied gas medium

By computations we demonstrate a new form of interaction between aerosol particles—a photophoretic interaction of a gas-kinetic nature that emerges when the particles are illuminated in a rarefied gas medium. Under the effect of light, the temperatures of particles differ from the temperature of the ambient gas and, under the effect of other particles in the gas medium, upsets the uniformity of accommodation of molecular energy and momentum over the surface of these particles to bring forth forces affecting the particles. Photophoretic forces were calculated on the basis of a free molecular flow regime approximation and a previously developed Monte Carlo algorithm. Calculations showed that when submicron particles that are soot-like in their optical properties are irradiated with solar light, significant repulsive forces arise between them that are by orders of magnitude higher than gravity, and these forces decrease approximately as the inverse square of the distance between the particles. Forces calculated for the free-molecule approximation are fairly accurate for a rarefied gas when the Knudsen number of the aerosol system is greater than one. Molecular collisions essentially decrease the photophoretic interaction forces for low Knudsen number. Photophoretic repulsion can be increased manyfold as the intensity of the incident radiation increases. Photophoretic interaction results not only in the repulsion of particles but can also be the cause of their attraction. For example, at night in the Earth's atmosphere at altitudes close to the stratopause the particles do not repulse but are attracted to each other. A study of individual aerosol particles interacting with clusters demonstrates noticeable spatial asymmetry of this interaction. The photophoretic interaction is shown to decrease the coagulation constant of submicron particles strongly absorbing radiation by orders of magnitude compared to the constant in darkness, even at an intensity of the external radiation equal to the solar light intensity. The significant effect of the photophoretic interaction on coagulation has been demonstrated.

A modeling study of seasonal variations of sea ice and plankton in the Bering and Chukchi Seas during 2007–2008

A nutrient (N), phytoplankton (P), zooplankton (Z), and detritus (D) ecosystem model coupled to an ice‐ocean model was applied to the Bering and Chukchi Seas for 2007–2008. The model reasonably reproduces the seasonal cycles of sea ice, phytoplankton, and zooplankton in the Bering–Chukchi Seas. The spatial variation of the phytoplankton bloom was predominantly controlled by the retreat of sea ice and the increased gradient of the water temperature from the south to the north. The model captures the basic structure of the measured nutrients and chl‐a along the Bering shelf during 4–23 July 2008, and along the Chukchi shelf during 5–12 August 2007. In summer 2008, the Green Belt bloom was not observed by either the satellite measurements or the model. The model‐data comparison and analysis reveal the complexity of the lower trophic dynamics in the Bering and Chukchi Seas. The complexity is due to the nature that the physical and biological components interact at different manners in time and space, even in response to a same climate forcing, over the physically distinct geographic settings such as in the Bering and North Aleutian Slopes, deep Bering basins, Bering shelf, and Chukchi Sea. Sensitivity studies were conducted to reveal the underlying mechanisms (i.e., the bottom‐up effects) of the Bering–Chukchi ecosystem in response to changes in light intensity, nutrient input from open boundaries, and air temperature. It was found that (1) a 10% increase in solar radiation or light intensity for the entire year has a small impact on the intensity and timing of the bloom in the physical–biological system since the light is not a limiting factor in the study region; (2) a 20% increase in nutrients from all the open boundaries results in an overall 7% increase in phytoplankton, with the Slope region being the largest, and the Bering shelf and Chukchi being the smallest; and (3) an increase in air temperature by 2°C over the entire calculation period can result in an overall increase in phytoplankton by 11%.

A Solar Power Storage Trolley

In order to improve the accumulating efficiency of solar energy, we designed a trolley with a 2-DOF attitude regulation structure of solar panels. In it, a solar orientation sensor was used to detect the solar orientation and the solar light intensity. A trolley’s differential wheels and a steering engine were used to keep the solar panels of the trolley vertically facing the Sun. At a certain interval, the steering engine adjusted the elevation angle of the solar panels and the trolley’s differential wheels adjusted the solar panels’ azimuth angle. Test experiment results show that the trolley can improve the accumulating efficiency of solar energy.

Diffusion Length in Nanoporous Photoelectrodes of Dye-Sensitized Solar Cells under Operating Conditions Measured by Photocurrent Microscopy.

We determined the carrier diffusion lengths in nanoporous layers of dye-sensitized solar cells by using scanning photocurrent microscopy. The diffusion lengths were found to be 60-100 μm for the conventional cells. In addition, we found a correlation between the carrier diffusion lengths and the cell efficiency, which proved that improvement in the diffusion length is one of the crucial factors for optimizing device performance. The diffusion length was measured for various operating conditions by varying parameters such as solar light intensity and applied electrical voltage. In particular, we observed electric-field-driven, carrier transport phenomena (i.e., drift current) in modified cells. Fitting with the drift-diffusion model enabled us to extract the electric field strengths present in the TiO2 nanoporous layer.

Facile fabrication of dye-sensitized solar cells utilizing carbon nanotubes grown over 2D hexagonal bimetallic ordered mesoporous materials

High-surface area and well-ordered mesoporous Fe incorporated SBA-15 (Fe-SBA-15), Fe–Cr incorporated SBA-15 (Fe–Cr-SBA-15) and Cr incorporated SBA-15 (Cr-SBA-15) catalysts are synthesized following a controlled post synthesis grafting process. The activities of all the catalysts are tested systematically and quantitatively towards the production of carbon nanotubes (CNTs) by chemical vapour deposition. In order to obtain CNTs with high quality and quantity, the parameters like temperature, reaction time and gas flow rate are optimized. Under optimum conditions, the Fe–Cr-SBA-15 catalyst is produced with high yield and uniform diameter of CNTs. The transmission electron microscopy result reveals high purity and well-graphitized structure of CNTs. The synthesized CNTs are used as counter electrode material for dye-sensitized solar cells (DSSCs). The CNTs based counter electrode shows good chemical stability, lower charge-transfer resistance and higher electrocatalytic activity towards I3−/I− redox reaction than that of platinum (Pt) counter electrode. The energy conversion efficiency of the CNTs counter electrode based DSSCs reaches 8.86% under irradiation with a simulated solar light intensity of 100 mW cm−2. The results prove that CNTs are one of the suitable candidates for Pt free counter electrode for DSSCs.

On the structure and function of “chlorosomes” of green bacteria

An assertion is substantiated that what is widely termed the chlorosomes of green bacteria are not bioparticles, but simply microscopic bacteriochlorophyll c crystals. Apparently, formation of a “chlorosome” represents the first, largely unsuccessful, evolutionary attempt to create a regulatory mechanism that would respond to variations in the intensity of solar light reaching the earth surface. Without bacteriochlorophyll cooperation with proteins, this was a dead end.

Role of iron species in the photo-transformation of phenol in artificial and natural seawater

The role played by iron oxides (goethite and akaganeite) and iron(II)/(III) species as photo-sensitizers toward the transformation of organic matter was examined in saline water using phenol as a model molecule. The study was carried out in NaCl 0.7M solution at pH 8, artificial (ASW) and natural (NSW) seawater, in a device simulating solar light spectrum and intensity. Under illumination phenol decomposition occurs in all the investigated cases. Conversely, dark experiments show that no reaction takes place, implying that phenol transformation is a light- activated process. Following the addition of Fe(II) ions to aerated solutions, Fe(II) is easily oxidized to Fe(III) and hydrogen peroxide is formed. Regardless of the addition of Fe(II) or Fe(III) ions, photo-activated degradation is mediated by Fe(III) species.Several (and different) hydroxylated and halogenated intermediates were identified. In ASW, akaganeite promotes the formation of ortho and para chloro derivatives (2- and 4-chlorophenol, 2,4-dichlorophenol and 2,4,6-trichlorophenol), while goethite induces the formation of 3-chlorophenol and bromophenols. Conversely, Fe(II) or Fe(III) addition causes the formation of 3- and 4-chlorophenol and 2,3- or 3,4-dichlorophenol. 4-Bromophenol was only identified when irradiating Fe(II) spiked solutions.Natural seawater sampled in the Gulf of Trieste, Italy, has been spiked with phenol and irradiated. Phenol photo-induced transformation in NSW mediated by natural photosensitizers occurs and leads to the formation of numerous halophenols, condensed products and nitrophenols. When NSW is spiked with phenol and iron oxides, Fe(II) or Fe(III), halophenols production is enhanced. A close analogy exists between Fe(III), Fe(II)/goethite in ASW and NSW products. Different halophenols production in the natural seawater samples depends on Fe(II)/goethite (above all for 3-chlorophenol, 2,3-dichlorophenol and 4-bromophenol formation) and on Fe(III) colloidal species (3-chlorophenol).

Treatment of Color Filter Wastewater by Fresnel Lens Enhanced Solar Photo-Fenton Process

Treatment of color filter wastewater using solar photo-Fenton process enhanced by high-concentrating Fresnel lens was investigated in this paper. Optimal reaction conditions based on response surface methodology (RSM) were established as under an initial pH of 5, a [H2O2]0/COD0ratio of 1~1.35 and a [H2O2]0/[Fe2+]0ratio of 15 for a reaction time of 60 min, which could reach a readily biodegradable level, that is, the biodegradability (BOD5/COD) of wastewater was more than 0.3. With the assistance of Fresnel lens, the solar photo-Fenton process increased the COD degradation rate and mineralization rate by a factor of 4.5 and 6.5, respectively. In addition, the microtoxicity (TU50) of wastewater was almost diminished after a 60 min of treatment, whereas the microtoxicity of treated wastewater without the assistance of Fresnel lens remained a TU50value of 1.166. This could be mainly due to the concentrating effect of Fresnel lens for solar energy, resulting in an increase of 2~3 times of solar light intensity and a raising heat irradiation in terms of 15~30 °C of wastewater temperature. These results revealed that solar energy could be concentrated effectively by using Fresnel lens and showed a significant promoting effect on the photo-Fenton reaction for treating color filter wastewater.

Solar Photocatalytic Degradation of Azo Dye in AqueousTiO2Suspension Assisted by Fresnel Lens

Solar TiO2photocatalytic process assisted by a Fresnel lens was investigated for treating an azo dye wastewater of Acid Orange 10 (AO10). Response surface methodology (RSM) was employed to assess the effect of critical process parameters (including initial pH of wastewater, concentration of TiO2, and reaction time) on treatment performance in terms of COD and TOC degradation efficiency. Optimized reaction conditions based on the analysis of RSM were established under an initial pH of 6.0, a concentration of TiO2of 1 g/L, and a reaction time of 2 h for reaching a 90% COD and TOC degradation of AO10 wastewater. With the assistance of Fresnel lens, the TOC degradation rate of AO10 wastewater increased significantly from 0.606 h−1and 0.289 h−1to 1.477 h−1and 0.866 h−1in summer (June) season (UV280–400 nm nm: 39.9–44.8 W/m2) and winter (December) season (UV280–400 nm nm: 23.9–26.9 W/m2), respectively. This could be mainly due to the concentrating effect of Fresnel lens for solar energy, resulting in an increase of 2~2.5 times of solar light intensity and a raising heat irradiation in terms of 10~15 °C of wastewater temperature. These results revealed that solar energy could be concentrated effectively by using Fresnel lens and showed a significant promoting effect on the TiO2photocatalytic degradation of dye wastewater.

Low temperature preparation of a high performance Pt/SWCNT counter electrode for flexible dye-sensitized solar cells

A platinum/single-wall carbon nanotube (Pt/SWCNT) film was sprayed onto a flexible indium-doped tin oxide coated polyethylene naphthalate (ITO/PEN) substrate to form a counter electrode for use in a flexible dye-sensitized solar cell using a vacuum thermal decomposition method at low temperature (120 °C). The obtained Pt/SWCNT electrode showed good chemical stability and light transmittance and had lower charge transfer resistance and higher electrocatalytic activity for the I 3 −/I − redox reaction compared to the flexible Pt electrode or a commercial Pt/Ti electrode. The light-to-electric energy conversion efficiency of the flexible DSSC based on the Pt/SWCNT/ITO/PEN counter electrode and the TiO 2/Ti photoanode reached 5.96% under irradiation with a simulated solar light intensity of 100 mW cm −2. The efficiency was increased by 25.74% compared to the flexible DSSC with an unmodified Pt counter electrode.

Outdoor H2 production in a 50-L tubular photobioreactor by means of a sulfur-deprived culture of the microalga Chlamydomonas reinhardtii

In the past decade, H₂ production using the green microalga Chlamydomonas reinhardtii has been extensively studied under laboratory-scale photobioreactors, while information on outdoor cultures is still lacking. In this paper, the results of experiments conducted with sulfur-deprived cultures of C. reinhardtii carried out in a 50-L horizontal tubular photobioreactor are presented. Hydrogen production experiments were carried out under both artificial and direct solar light. In both cases, the H₂ output attained was 18-20% of what obtained in the laboratory. However, no significant changes in the H₂ production were observed when cells grown outdoors were tested under laboratory conditions. Chlorophyll fluorescence measurements showed that outdoor cultures were subjected to strong photo-inhibition, due to the combination of high solar light intensity and sulfur-deprivation. Indeed, H₂ production was only achieved outdoors when cultures were previously acclimated to sunlight, a condition that caused a number of physiological changes, namely: (i) a decrease in the chlorophyll content per unit of dry weight; (ii) an increase in the photosynthesis and respiration rates, and (iii) a higher induction of the xanthophyll cycle pigments as compared to non-acclimated cultures. It was concluded that the reduced H₂ output achieved in the 50-L photobioreactor was due to the different illumination pattern to which the cultures were exposed (one-sided vs. two-sided illumination provided in the laboratory), as well as to the great difference in the mixing times (60 min vs. 15.5s achieved in the lab-scale photobioreactor). To the very best of our knowledge this is the first time that H₂ production with green algae has been achieved by means of solar light.

Polyvinyl pyrrolidone aided preparation of TiO 2 films used in flexible dye-sensitized solar cells

Polyvinyl pyrrolidone (PVP) is introduced to low temperature preparation of a good quality TiO 2 film used in flexible dye-sensitized solar cells (DSSCs). The samples are characterized by scanning electron microscopy and UV–vis absorption spectra, the photovoltaic performance of the DSSC is measured. It is found that PVP can improve the dispersion of TiO 2 particles and the adherence of TiO 2 particles to flexible substrate, as well as the adsorption of sensitized dye to TiO 2 film. Additionally, ultraviolet light irradiation can eliminate organics remained on the surface the TiO 2 film and improve the surface state of TiO 2 film. Under an optimal condition, a flexible DSSC using TiO 2 film doped PVP and UV irradiation treated achieves a light-to-electric energy conversion efficiency of 3.02% under irradiation with a simulate solar light intensity of 100 mW cm −2.

A solid-phase chemical actinometer film for measurement of solar UV penetration into snowpack

A solid-phase actinometer system suitable for measuring 295–400 nm solar light intensity and penetration into snowpack has been developed and field-tested. Snow and atmospheric chemists are concerned with ultraviolet light irradiance as this spectral range has been linked to NOx and ·OH radical formation within snowpack. The actinometer, prepared as thin films, consists of 2-nitrobenzaldehyde (2NB) dispersed in a polymethylmethacrylate (PMMA) matrix. The concentration of 2NB at the film surface decreases due to ultraviolet light exposure and is quantified using attenuated total reflectance infrared spectroscopy (ATR-IR); either relative or absolute light intensity can be determined. The films are inexpensive, physically robust and can be easily deployed in cold-weather environments that are inhospitable to electronic instrumentation or liquid actinometer systems. Measurements of light penetration into seasonal snowpack near Barrow, Alaska, were made in 2007 and 2008. E-folding depths of 8–26 cm were observed, depending on snow conditions; alternatively, the depth of snow required to attenuate 75% of solar UV-A incident on the snowpack surface was found to range from < 5 cm for aged snowpack to 15 cm for snowpacks undergoing annual melting. The variation in penetration depth is dependent on the recent history of the snowpack and is likely to determine the extent of photochemical transformations occurring within the snowpack.