Search Results (3)

Snow covers are greatly affected by particles deposited on their surface. In this work, an experimental campaign was carried out in the Sierra Nevada (Granada, Spain). The optical effect of different contaminating particles on the snow covers was measured using a field spectroradiometric system composed of three upwelling spectroradiometers and three downwelling ones. Sand collected from a Mediterranean beach (Spain), ash collected from the La Palma volcano eruption, haze collected from an event that occurred in Spain, and soot collected from a diesel vehicle were employed for contaminating the snow. Soot, ash, and sand were analysed with X-ray diffraction to obtain their mineralogical composition or their structural characteristics, whereas haze's mineralogical composition was obtained from the literature. From this information, the refractive index of each material was weigh-averaged, considering the refractive indices of their components. After measurements, snow samples were filtered and weighted to evaluate the particle concentrations in the snow. Previous contamination with soot was observed due to the existence of a nearby road. Snow albedo was calculated with the OptiPar model. The experimental and modelled results show that contaminating with sand decreases the snow albedo in the visible range whereas it increases the albedo in the infrared range. However, the rest of the materials lead to a decrease in the albedo in the whole spectrum, although with different intensities depending on the wavelength range. Full article

Snow covers are very sensitive to contamination from soot agglomerates derived from vehicles. A spectroradiometric system covering a wavelength from 300 to 2500 nm with variable resolution (from 2.2 to 7.0 nm) was used to characterize the effect of soot derived from a diesel vehicle whose exhaust stream was oriented towards a limited snowed area. The vehicle was previously tested in a rolling test bench where particle number emissions and size distributions were measured, and fractal analysis of particle microscopic images was made after collecting individual agglomerates by means of an electrostatizing sampler. Finally, the experimental results were compared to modelled results of contaminated snow spectral albedo obtained with a snow radiative transfer model developed by our research group (OptiPar) and with other models. Both experimental and modelled results show that increasingly accumulated soot mass reduces the snow albedo with a constant rate of around 0.03 units per mg/kg, with a predominant effect on the UV-VIS range. Based on the small size of the primary particles (around 25 nm), the Rayleigh-Debye-Gans approximation, further corrected to account for the effect of multiple scattering within the agglomerates, was revealed as an appropriate technique in the model. Full article

The broadband surface albedo of snow can greatly be reduced by the deposition of light-absorbing impurities, such as black carbon on or near its surface. Such a reduction increases the absorption of solar radiation and may initiate or accelerate snowmelt and snow albedo feedback. Coincident measurements of both black carbon concentration and broadband snow albedo may be difficult to obtain in field studies; however, using the relationship developed in this simple model sensitivity study, black carbon mass densities deposited can be estimated from changes in measured broadband snow albedo, and vice versa. Here, the relationship between the areal mass density of black carbon found near the snow surface to the amount of albedo reduction was investigated using the popular snow radiative transfer model Snow, Ice, and Aerosol Radiation (SNICAR). We found this relationship to be linear for realistic amounts of black carbon mass concentrations, such as those found in snow at remote locations. We applied this relationship to measurements of broadband albedo in the Chilean Andes to estimate how vehicular emissions contributed to black carbon (BC) deposition that was previously unquantified. Full article