The properties and behavior of α-pinene secondary organic aerosol particles exposed to ammonia under dry conditions

with carboxylic acids on the particle surface, leading to a slight increase in particle size. We show that the reaction products form a solid semi-volatile coating that is a few nanometers thick. This solid coating prevents coagulating particles from coalescing for over two days. However, when the gas phase is diluted this semi-volatile coating evaporates in minutes, which is ensued by rapid coalescence. The ammoniated products in the particle bulk affect particles' evaporation kinetics, more so for the smaller particles that contain a higher fraction of ammoniated products.