Conventional cooling systems, that is, air conditioners, should be replaced because they consume a substantial amount of energy and cause environmental pollution. In this context, radiative cooling systems, which perform cooling without consuming any energy or causing environmental pollution, are emerging as an alternative. However, most of the radiative coolers explored thus far include metals, such as silver, that are used as solar reflectors, thereby entailing problems in terms of practicality, mass production, cost, and light pollution. Herein, we propose calcium carbonate (CaCO3) micro-particle-based radiative cooling, which utilizes the high-energy band gap of CaCO3 for high-performance radiative cooling. As the cooler has only a single layer of a CaCO3 composite without any metal reflector, it is mass-producible, cheap, and does not cause light pollution. To demonstrate the cooling performance of CaCO3, optical properties and temperature changes are measured and compared with those of commercial white paint. As a result, it is demonstrated that the CaCO3-based radiative cooler has cooling power 93.1 W/m2 in calculation and can be cooled 6.52 ℃ and 3.38 ℃ under ambient temperature in daytime and nighttime respectively. Thus, it can perform as radiative cooler in entire day.
