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.

中文翻译：

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准确量化晴空辐射冷却潜力：对基于透射率的近似值的温度校正

辐射冷却材料冷却潜力的理论计算对于确定其在不同气象条件下的冷却能力和评估其性能至关重要。为了便于这些计算，需要长波红外下涌大气辐照度的准确模型。然而，基于透射率的余弦近似广泛用于确定晴空条件下的辐射冷却潜力，但并未考虑由于热量损失到大气本身较冷区域而产生的冷却潜力。在这里，我们表明使用近似值会导致相对于 MODTRAN 6 输出的冷却潜力低估 > 10%。我们建议对基于透射率的近似值进行温度校正，这说明了冷高层大气的热量损失，并显着减少了这种低估，同时保留了原始模型的优点。鉴于基于透射率的模型的广泛和持续使用，我们的结果突出了晴空辐射冷却潜力计算中潜在误差的一个重要来源以及纠正它们的方法。