Effects of humidity, aerosol, and cloud on subambient radiative cooling

Passive radiative cooling provides an eco-friendly solution for space cooling by spontaneously emitting thermal radiation to the cold higher sky through the atmospheric windows. The cooling performance of a radiative cooler is influenced by various environmental factors such as humidity, aerosol level, and cloud coverage, of which a comprehensive understanding is yet to be developed. Herein, we propose a theoretical model, which only requires the input of ground-level atmospheric parameters, to quantitatively evaluate the effects of different environmental factors on a radiator. Particularly, the vertical variations of both vapor concentration and temperature in the atmosphere, which are often missed in previous models, are found to remarkably influence the radiative cooling performance. Moreover, both aerosol scattering and cloud coverage can largely weaken the cooling performance while both are closely correlated to the humidity. The design strategies of radiative coolers in different climates are then explored. Based on the various environmental parameters relevant to the geographic locations, the potential of applying the spectrally selective radiative cooling technology in different regions is also evaluated and mapped.