Droplets From Mold May Seed Rain Forest Aerosols

Organic aerosol particles that form in the air above the Amazon rain forest likely arise from potassium-rich droplets emitted from rain forest flora and fauna, especially molds (Science, DOI: 10.1126/science.1223264). So-called secondary organic aerosols form from oxidation of airborne organic gases and play key roles in weather and climate by seeding clouds and absorbing or scattering sunlight, but their origin and properties are poorly understood. A research group led by Christopher Pöhlker, Ulrich Pöschl, and Meinrat O. Andreae of Germany’s Max Planck Institute for Chemistry studied aerosols in the Amazon basin, far from urban emissions. They found that all particles contained potassium, from 20% by mass for particles 0.15 µm in diameter to 0.3% for particles 1 µm in diameter. The researchers propose that Amazonian organisms emit potassium-rich aqueous droplets that undergo multiphase chemical reactions to produce secondary organic components. Fungal species in particular are known to emit droplets containing potassium when they discharge spores. The group is now working to understand emission rates and mechanisms and to determine whether similar processes are at work in other environments.