Deadline for manuscript submissions: 24 April 2020.

Dear Colleagues,

Although we call what we breathe “air”, it is by no means a molecular mixture of nitrogen, hydrogen, and oxygen. The ambient air is full of tiny particles, which—along with gas molecules—form aerosols. Aerosol particles in the Earth’s troposphere originate from either direct emission (i.e., primary particles) or in-situ nucleation (i.e., secondary particles). While nucleation itself is a fundamental physico-chemical process, which is important wherever second-order phase transitions occur, secondary particles formed via nucleation (or new particle formation (NPF)) dominates particle number concentrations in many parts of the troposphere and has important implications for air quality and climate. Although the typical size of particles nucleating in the atmosphere seldom exceeds a couple of nanometers, their impact on a wide range of properties of large- and global-scale atmospheric systems is very strong. In particular, atmospheric models are very sensitive to rates at which such particles nucleate under atmospheric conditions. Atmospheric nucleation occurs at the edge of molecular scale and nanoscale, and thus its rates are very sensitive to the initial steps of the particle formation, at which nucleating particles are in a state that is neither gaseous nor liquid, but in the indeterminate state of molecular cluster. Since molecular clusters are deeply within the quantum region, their interactions with condensable vapor molecules and each other are controlled by the corresponding wave functions. Cluster–molecule and cluster–cluster interactions at the quantum level strongly impact rates at which secondary particles nucleate in the Earth’s atmosphere, which in turn largely control the physico-chemical properties of (macroscopic) atmospheric systems at local, regional, and global levels. This means that nucleation is a bridge between the quantum world and the planetary atmosphere. The bridge is yet to be built, as atmospheric nucleation mechanisms, chemical composition of nucleating particles, and rates at which they nucleate in the Earth’s atmosphere are still puzzling. We invite theoreticians, experimentalists, modelers, and data analysts to share their expertise, knowledge, and passion for atmospheric nucleation with the audience of Atmosphere, and to contribute to this Special Issue by submitting research articles, rapid communications, and reviews dedicated to this puzzling phenomenon.

Dr. Alexey B. Nadykto
Dr. Yisheng Xu
Prof. Dr. Qingzhu Zhang
Guest Editors