Scientists have observed frequent formation of new particles at high temperatures close to 40 °C during heat waves.[1] Multifunctional carboxylic acids, such as di- and triacids, form the main component of nanoparticles in the nucleation mode with a size of 3 to 25 nm, while the proportion of sulfuric acid increases with increasing size.[1] Using field observation and quantum-chemical calculations, they measured the chemical composition of nanoparticles as small as 3 nm.[1] The study revealed a spontaneous mechanism for the formation of supramolecular organic nanoparticles through the self-assembly of carboxylic acids by hydrogen bonds.[1] This mechanism explains the unexpected new formation of particles at high temperatures, which traditional theories based on volatility do not explain.[1] The findings have implications for assessing the impact of aerosols on cloud formation, public health and climate in relation to more frequent heat waves caused by global warming.[1]