Mechanistic insights into secondary organic aerosol formation from particle growth characteristics
Authors
Rahul Zaveri — Pacific Northwest National Laboratory
John E Shilling — Pacific Northwest National Laboratory
Chen Song — Pacific Northwest National Laboratory
Mikhail S. Pekour — Pacific Northwest National Laboratory
Dick C Easter — Pacific Northwest National Laboratory
Category
Modeling
Description
Several recent studies suggest that secondary organic aerosol (SOA) quickly becomes viscous and relatively non-volatile after formation, such that it does not evaporate upon dilution. However, the physical mechanism of SOA formation process itself still remains uncertain. SOA can form via three possible mechanisms:- Irreversible condensation of low volatility organic vapors
- reactive uptake of organic vapors
- Raoult’s Law-type absorption of organic vapors into pre-existing organic aerosol, followed by in-particle conversion to viscous, low-volatility products.
SOA formation via the first two mechanisms would be gas-phase diffusion-limited, and the growth will be controlled by aerosol surface area, while Raoult’s Law-based absorption and particle-phase chemistry would be controlled by aerosol volume. The size distributions resulting from these processes would be quite different. In this study, we probe the mechanism of SOA formation from a-pinene photooxidation in an environmental chamber by interpreting the observed evolution of aerosol size distributions with the MOSAIC box-model, which treats aerosol size distribution evolution due to coagulation and dynamic, multicomponent gas-particle mass transfer. The poster will describe the experimental and modeling approaches and discuss the mechanistic insights gained from this type of analysis.