Tiny, invisible aerosol particles in the atmosphere significantly influence Earth’s temperature and cloud formation. For a long time, scientists operated under the assumption that intense heat prevented these particles from forming, believing high temperatures would simply cause atmospheric gases to evaporate.However, a surprising new study published in the journal Science reveals that heat waves actually trigger the creation of new aerosol particles, even at sweltering temperatures of 40°C (104°F).Intense sunlight during a heat wave triggers chemical reactions in the atmosphere. These reactions convert gases, which are emitted by both human activities and plants, into organic acids. These acid molecules then spontaneously aggregate, acting like tiny building blocks, to form solid nanoparticles as small as 3 nanometers.Typically, atmospheric aerosols act as “seeds” that attract water vapor to build clouds. These clouds then act like a giant sunshade to help cool the planet. But there is a major catch with these newly discovered, heat-born particles: they repel water.Because these specific nanoparticles cannot easily gather moisture, they fail to form cooling clouds. Without a protective cloud cover, more sunlight blasts the Earth’s surface, making the heat wave even more severe. This creates a dangerous feedback loop: hotter temperatures create more water-repelling particles, which in turn lead to even less cloud cover and more warming.In addition to their climate impact, these nanoparticles pose a direct threat to public health. Due to their extremely small size, they can be easily inhaled deep into the lungs and can enter other organs, leading to inflammation and cellular stress.Researchers are optimistic that this newly discovered mechanism will assist scientists in refining future climate models and in shaping public health policies as global heat waves become more frequent.