The reason why the French fight heat with white chalk

As heat waves become more frequent and intense due to rising global temperatures, endangering populations in cities, many people are looking for an unexpected, simple and cheap solution. In France, demand for a powder called Blanc de Meudon (Meudon powder) is skyrocketing. To cope with record high temperatures, people use this type of chalk to protect against heat and paint on windows in schools and private homes. When mixed with water and applied to glass, the opaque white coating allows light to pass through but reflects heat, helping to cool the home.

Theo IFL Sciencewhite paint on walls and roofs is famous for its cooling effect. White surfaces reflect sunlight and heat while dark surfaces absorb. White paint on the market can reduce the temperature by at least 1.7 degrees Celsius compared to the ambient temperature at noon. Even super white paint not only reflects sunlight but also radiates heat through the “radiative cooling” process, helping to reduce indoor temperatures by several degrees Celsius.

Theo BBCa study on super white paint by scientists at Purdue University in Indiana, USA, found that the paint layer can reflect up to 98.1% of sunlight, much higher than regular white paint (85%). When combined with super black primer, it can reduce daytime temperatures by up to 7.6 degrees Celsius.

One of the reasons why chalk has an effective cooling effect lies in the properties of the main ingredient calcium carbonate (CaCO3), which not only has high reflectivity but also withstands solar radiation well. According to Xiangyu Li, a scientist at the Cooling Technology Research Center at Purdue University, because it is mainly composed of CaCO3, chalk absorbs very little sunlight, including the visible light range. At the same time, chalk does not absorb ultraviolet rays and very little near-infrared light, so this is the ideal choice to reflect all sunlight. This property has prompted some researchers to use calcium carbonate nanoparticles in new super-cool paints. Additionally, chalk is relatively benign in terms of health and environmental impacts, although there are some risks to the respiratory system from inhaling chalk dust indoors.

Demand for Blanc de Meudon has led to shortages across the country as people struggle with temperatures above 40 degrees Celsius. Blanc de Meudon is often used to whiten shop windows during repairs or garden greenhouses. Currently, this powder application is expanding to schools and apartments. In addition to being cheap, chalk powder does not consume much electricity, exacerbating the heat effect and exhaust problems like air conditioning.

Besides using powder, European countries apply many other creative heat protection solutions. According to Fast Companythe government of Paris, France, designed many “cooling islands” that use water, trees and shade structures to maintain a cooler space of about 2.2 – 3.9 degrees Celsius. Currently, the city has increased the number of cooling islands from more than 800 in 2019 to more than 1,400.

In Barcelona, ​​Spain, the subway uses an AI ventilation control system to monitor air quality and temperature, helping to reduce temperatures at stations by nearly 1.3 degrees Celsius. Meanwhile, in Amsterdam, the Netherlands, authorities recommend residents hang curtains or blankets outside their windows to cool down in the summer.