Clouds' Clout on the Aerosol Size Distribution - Modelling Detailed Chemical Processing

Clouds have, by introducing the liquid phase as a chemical reaction chamber, the ability to change the aerosol size distribution. In as short as 40 minutes, the mass of an aerosol particle can increase by an order of magnitude due to chemical processing, with commensurate impacts on the precipitation efficiency and cloud optical properties. To study the chemical processing of aerosols in clouds, we developed the Chemical Mechanism Integrator (Cminor), a new, open-source, stand-alone Fortran environment for particle-based simulation of chemical multiphase mechanisms. Cminor employs advanced mathematical techniques tailored to heavily exploit the structure of chemical kinetic systems, multiple aqueous phases, and efficient evaluation of rate constants. Cminor uses the idea of Lagrangian cloud microphysics, i.e., computational particles, each representing a multitude of identical particles (e.g., aerosol particles of specific chemical composition). In addition to chemistry, Cminor predicts the activation of aerosol particles to cloud droplets and their subsequent growth by condensation, which enables us to directly investigate some impacts of the processed aerosol size distribution on cloud microphysics. While Cminor is currently applied in an adiabatic parcel framework, in which the influence of chemical processing on the aerosol size distribution is reliably captured, it will be coupled to a three-dimensional large-eddy simulation model shortly, which allows us to investigate the interactions of atmospheric chemistry, dynamics, and cloud physics with an unprecedented degree of detail.