Accurately Quantifying Clear-Sky Radiative Cooling Potentials: A Temperature Correction to the Transmittance-Based Approximation

• Published in: Atmosphere Vol. 12; no. 9; p. 1195
• Main Authors: Mandal, Jyotirmoy, Huang, Xin, Raman, Aaswath P.
• Format: Journal Article
• Language: English
• Published: Basel MDPI AG 01.09.2021
• Subjects: Approximation; Atmosphere; atmospheric irradiance; Atmospheric models; atmospheric optics; Carbon dioxide; Clear sky; Cooling; cooling potential; Downwelling; Geoengineering; Greenhouse gases; Heat; Heat loss; Irradiance; Mathematical analysis; Meteorological conditions; MODTRAN; Radiation; Radiative cooling; Sky; Temperature; Transmittance; transmittance model; Upper atmosphere
• ISSN: 2073-4433; 2073-4433
• DOI: 10.3390/atmos12091195

Theoretical calculations of the cooling potential of radiative cooling materials are crucial for determining their cooling capability under different meteorological conditions and evaluating their performance. To facilitate these calculations, accurate models of long-wave infrared downwelling atmospheric irradiance are needed. However, the transmittance-based cosine approximation, which is widely used to determine radiative cooling potentials under clear sky conditions, does not account for the cooling potential arising from heat loss to the colder reaches of the atmosphere itself. Here, we show that use of the approximation can lead to >10% underestimation of the cooling potential relative to MODTRAN 6 outputs. We propose a temperature correction to the transmittance-based approximation, which accounts for heat loss to the cold upper atmosphere, and significantly reduces this underestimation, while retaining the advantages of the original model. In light of the widespread and continued use of the transmittance-based model, our results highlight an important source of potential errors in the calculation of clear sky radiative cooling potentials and a means to correct for them.