text: While passive radiative cooling technologies have proven successful in mid-latitude regions of Earth, to reach the same level of performance has faced more difficulties in tropical climates. This has primarily been attributed to the higher solar irradiance and atmospheric radiation of these zones, particularly humidity and cloud cover. The average cooling potential of hot and humid climates varies between 10 and 40 W/m2, which is significantly lower than hot and dry climates.
  For example, the cooling potential of most of southeast Asia and the Indian subcontinent is significantly diminished in the summer due to a dramatic increase in humidity, dropping as low as 10–30 W/m2. Other similar zones, such as tropical savannah areas in Africa, see a more modest decline during summer, dropping to 20–40 W/m2. However, tropical regions generally have a higher albedo or radiative forcing due to sustained cloud cover and thus their land surface contributes less to planetary albedo.
  A study by Han et al. determined criteria for a PDRC surface in tropical climates to have a solar reflectance of at least 97% and an infrared emittance of at least 80% to achieve sub-ambient temperatures in tropical climates. The researchers used a  Barium sulphate|-Potassium sulphate| coating with a "solar reflectance and infrared emittance (8–13 μm) of 98.4% and 95% respectively" in the tropical climate of Singapore and achieved a "sustained daytime sub-ambient temperature of 2°C" under direct solar intensity of 1000 W/m2.