Probing the Molecular Basis of the "Burying" Mechanism: An Additional Route to Secondary Organic Aerosol (SOA) Particle Growth

University Of California-Irvine, Irvine CA

Investigators

Abstract

This project investigates a novel mechanism for the growth of secondary organic aerosol (SOA) particles in the atmosphere. Uncertainties in the growth mechanisms of solid and semi-solid SOA particles limit the ability to predict their impacts on visibility, air quality, and atmospheric processes, and hinder the development of effective control strategies. The research will provide the basic kinetic and thermodynamic data needed to improve this predictive capability by examining how gases interact with and become incorporated into highly viscous organic particles. Improving the ability to predict how atmospheric particles form and grow will strengthen understanding of atmospheric processes that influence air quality, visibility, and environmental conditions that affect communities and ecosystems. Understanding the surface composition of organic particles is central to understanding the interaction of incoming gases with the surface and how this affects their uptake and contribution to particle growth. On a molecular level, it is expected that the residence time of gases on the surface of highly viscous particles will play a major role in their net uptake, yet there are few data on the fundamental parameters that determine this residence time. The ultimate goal of this research is to elucidate a hypothesized "burying" mechanism that incorporates gas phase species into highly viscous particles. A central aspect of this “burying” mechanism is the nature of the gas-surface interaction. The specific objectives of the experiments are to: (1) measure uptake coefficients as a function of temperature for a series of gases of selected structures and functional groups on self-assembled monolayers (SAMs) having well-defined terminal groups that are also common components of SOA particles as well as on SOA itself; (2) carry out temperature-programmed thermal desorption studies of the selected gases initially adsorbed on the SAMs to obtain kinetics data that will allow rate constants for desorption at different temperatures to be determined; and (3) carry out studies of the impact of lower volatility species with unique signatures on the uptake of organic nitrates into SOA particles formed from the ozonolysis of selected biogenics, with a focus on α-pinene. This award reflects NSF's statutory mission and has been deemed worthy of support through evaluation using the Foundation's intellectual merit and broader impacts review criteria.