Is secondary organic aerosol yield governed by kinetic factors rather than equilibrium partitioning?

Abstract

The numerical description of the formation of secondary organic aerosol (SOA) in the atmosphere relies on the use of particle yields, which are often determined in chamber experiments. What is sometimes not appreciated is that such yields (i) can be defined in different ways and (ii) depend on atmospheric conditions. Here we show with the help of hypothetical scenario simulations that the differential SOA yield upon addition of oxidation products to an atmosphere already containing such products and SOA is more relevant in the ambient atmosphere than the commonly used integrative yield from chamber studies. Furthermore, we suggest that the SOA formation scenarios that have been studied so far comprise merely a subset of possible atmospheric situations. In particular, while in the standard scenarios factors such as volatility and aerosol loading are important, scenarios can be envisaged where these factors become less important while the differential yield approaches unity for all oxidation products. Finally, we suggest aerosol growth in the atmosphere should be seen as being determined by a dynamic situation arising from many simultaneously occurring kinetic processes rather than a thermodynamic equilibrium process.