Direct observation of atmospheric new-particle formation using air ion spectrometers

Aerosol particles play an important role in the Ea rth’s atmosphere and in the climate system: They scatter and absorb solar radiation, facilitate ch mical processes, and serve as seeds for cloud formation. Secondary new-particle formation (NPF) i s a globally important source of these particles. Currently, the mechanisms of particle formation and the vapors participating in this process are, howe ver, not truly understood. In order to fully explain atm ospheric NPF and subsequent growth, we need to measure directly the very initial steps of the form ation processes. Air ion spectrometers measure the mobility distributions of charged aerosol particles in the mobility diameter range of 0.8–42 nm. Neutr al cluster and air ion spectrometers measure additiona lly the mobility distribution of neutral particles larger than 2 nm in diameter by charging the aerosol sampl e with unipolar corona chargers. According to earli r studies, the atmospheric nucleation and cluster act ivation take place at the mobility diameter range o f 1.5–2 nm. Therefore, the ion spectrometers allow direct m easurements at exactly the size where atmospheric nucleation takes place. The results indicate that t he ion-induced nucleation contributes ~1-30% to the newparticle formation events in most atmospheric condi tions.