To cope with temperatures exceeding 40 degrees Celsius, many French citizens are using white chalk to reduce indoor heat, leading to a surge in sales for this product.
As heatwaves become more frequent and severe due to rising global temperatures, posing risks to urban residents, many are turning to an unexpected, simple, and affordable solution. In France, the demand for a powder known as Blanc de Meudon (Meudon chalk) is skyrocketing. To combat record-breaking temperatures, people are using this chalk to stay cool by applying it to the windows of schools and private homes. When mixed with water and painted onto glass, the opaque white coating allows light to pass through while reflecting heat, helping to cool the interior. According to IFL Science, white paint on walls and roofs is renowned for its cooling effect. White surfaces reflect sunlight and heat, whereas dark surfaces absorb them. Commercially available white paint can reduce temperatures by at least 1.7 degrees Celsius compared to the ambient temperature at noon. Furthermore, ultra-white paint not only reflects sunlight but also releases heat through radiative cooling, helping to lower indoor temperatures by several degrees. According to the BBC, a study on ultra-white paint by scientists at Purdue University in Indiana, USA, found that the coating can reflect up to 98.1 percent of sunlight, significantly higher than standard white paint at 85 percent. When combined with ultra-black primer, it can reduce daytime temperatures by up to 7.6 degrees Celsius. One reason chalk is an effective cooling agent lies in the properties of its main ingredient, calcium carbonate (CaCO3), which possesses high reflectivity and excellent resistance to solar radiation. According to Xiangyu Li, a scientist at the Cooling Technology Research Center at Purdue University, because it is primarily composed of CaCO3, chalk absorbs very little sunlight, including the visible light spectrum. Additionally, it does not absorb ultraviolet rays and absorbs very little near-infrared light, making it an ideal choice for reflecting sunlight. This property has prompted some researchers to incorporate calcium carbonate nanoparticles into new ultra-cooling paints. Moreover, chalk is relatively benign in terms of health and environmental impact, although there are some respiratory risks associated with inhaling chalk dust indoors.
Painting windows with white chalk powder can help keep indoor temperatures a few degrees cooler. Photo: TBS Bites
The demand for Blanc de Meudon has led to shortages across the country as residents struggle with temperatures above 40 degrees Celsius. Blanc de Meudon is typically used to paint shop windows during renovations or for greenhouses in gardens. Currently, the application of this powder is expanding to schools and apartment buildings. Beyond its low cost, the powder does not consume electricity, which would otherwise exacerbate the heat island effect and emissions issues associated with air conditioning. In addition to using chalk, European countries are adopting various other creative cooling solutions. According to Fast Company, the Paris municipal government has designed numerous cooling islands that utilize water, greenery, and shade structures to maintain spaces that are approximately 2.2 to 3.9 degrees Celsius cooler. Currently, the city has increased the number of these cooling islands from over 800 in 2019 to more than 1,400. In Barcelona, Spain, subway lines use AI-controlled ventilation systems to monitor air quality and temperature, helping to lower station temperatures by nearly 1.3 degrees Celsius. Meanwhile, in Amsterdam, the Netherlands, authorities recommend that residents hang curtains or blankets outside their windows to cool down during the summer.
Compiled by An Khang
