Fig. 4. Schematic representation of the atmospheric coevolution of BBA composition and INA.

The particle contains minerals depicted in shades of brown, soot depicted in black, and OA depicted in green. Evaporation of OA leads to increased availability of ice-active sites. Oxidation of OA changes its chemical composition to be more oxidized and water-soluble organic carbon such that, when the particle is immersed in a droplet, the OA can dissolve more readily to reveal ice-active sites. SOA condensation from oxidation and condensation of organic carbon onto the particle conceals ice-active sites. This schematic represents the different BBA aging processes that may occur in the atmosphere, which are not ordinarily decoupled as depicted and can occur simultaneously or in competition to varying degrees.