Many people know hydrogen peroxide as a hair bleaching agent or disinfectant. However, the substance is also produced high up in the atmosphere in clouds and raindrops. There it has a massive impact on air quality. Researchers from the Leibniz Institute for Tropospheric Research in Leipzig (TROPOS), together with international colleagues, have now discovered a previously unknown source of such oxidants. The discovery could explain where five to 15 percent of the hydrogen peroxide in the atmosphere comes from.
The team investigated so-called alpha-keto acids. These substances are released into the air from plants and industrial waste gases. Until now, scientists have underestimated their importance for the atmosphere. The new study shows: When sunlight hits these acids in cloud droplets, strong oxidizing agents are formed.
Laboratory experiments reveal chemical reaction
The scientists tested three different alpha-keto acids in the laboratory. They proved that these substances form hydroperoxides when combined with light. This then produces hydrogen peroxide. These reactions take place in tiny water droplets that float in the air or occur in clouds. Scientists from China, Israel, Italy and Germany took part in the study. TROPOS in Leipzig used the laboratory data in its CAPRAM computer model. This model can simulate very complex chemical reaction chains in the atmosphere.
Importance for air quality and climate forecasts
The discovery is of great significance. Oxidizing agents such as hydrogen peroxide influence how pollutants form and disappear in the air. They also affect the formation of particles that create clouds and influence the climate
However, important data is still lacking. The researchers are therefore calling for systematic measurements of keto acid concentrations in different regions. This is the only way to incorporate the new findings into climate models. "Thanks to the international cooperation, we have managed to find another piece of the puzzle in the very complex multiphase atmospheric chemistry," explains Professor Hartmut Herrmann from TROPOS.
