image: Figure 1 | Explanation and validation of the effect of haze on radiative cooling. (a-b), Schematic of passive daytime radiative cooling (PDRC) under clear and haze-polluted skies. Particulate matter (PM) in a haze-polluted atmosphere scatters both sunlight and infrared thermal radiation from the radiative cooler. While the former is beneficial, the latter is detrimental to PDRC. (c), Solar spectrum and atmospheric transmittance at various haze concentrations, indicated with various PM2.5. With the increase of PM2.5, the attenuation of solar radiation is more significant than that of atmospheric transmittance. This selective scattering is the basis of the analysis in this work.
Credit: Zhen Chen et al.
Urban heat islands (UHI) pose severe health risks, which are further aggravated by haze pollution from particulate matter (PM). Passive daytime radiative cooling (PDRC) offers a sustainable solution by reflecting sunlight and emitting heat to outer space; however, its performance under haze-polluted atmosphere remains unclear. In a new paper published in Light: Science & Applications, a team led by Professor Zhen Chen from Southeast University (China) develops a general framework to model and optimize PDRC under haze conditions. Their analysis reveals that haze selectively scatters sunlight more strongly than it degrades infrared thermal radiation through the atmospheric window. This asymmetry shifts the design priority: under haze-polluted skies, coolers should maximize infrared emission, even at the cost of slightly reduced solar reflectivity—a guideline that stands in marked contrast to clear-sky designs, which prioritize minimizing solar absorption.
To demonstrate this new guideline, the team optimized a polydimethylsiloxane (PDMS)-based transparent thermal emitter on a silver substrate. Theoretical and experimental results highlight the different design rules: while thinner coolers perform better under clear skies, thicker coolers excel in haze-polluted conditions due to enhanced infrared thermal emission. This work provides guidelines for designing radiative coolers in haze-polluted atmosphere.
As the scientists explain: "Our study reveals that haze pollution redefines the design rules for radiative cooling. While clear-sky designs focus on minimizing solar heating, haze‑polluted conditions call for maximizing infrared emission—an insight that also carries important implications for thermal design in desert, lunar, and Martian environments."
Journal
Light: Science & Applications
Article Title
Subambient daytime radiative cooling to mitigate haze-induced amplification of urban heat islands