Aerosol particles are ubiquitous in Earth's atmosphere, influencing the quality of life through their climatic and health effects and by affecting visibility. In recent years, the formation and growth of nanometer-scale particles have been observed in situ in many different atmospheric environments, including urban plumes, clean Arctic air, the continental boundary layer, and coastal environments. However, as Kulmala explains in his Perspective, the mechanisms of atmospheric nucleation have not yet been resolved. An interdisciplinary approach involving laboratory experiments, continuous field observations, new theories, and dynamic models will be required to determine which mechanisms dominate in different environments.
