Laboratory Investigations of Particle-Organic Vapor Interactions: Effects on Particle Formation, Growth, and Properties

This project is a collaborative effort among four institutions to improve understanding of the fundamental life cycle of atmospheric aerosol. The effort focuses on processes for the formation of very small particles in the atmosphere over a range of conditions. The goal of the proposed studies is to facilitate more accurate predictions of the influence of these particles on climate by conducting laboratory measurements that reduce uncertainties related to modeling their formation, growth and atmospherically important properties.

Together the project team has extensive capabilities that include the ability to produce primary aerosol particles such as soot and secondary organic aerosol (SOA), measure and control the particle size and mass distributions, control oxidative aging of such particles via hydroxyl radical and ozone reactions over equivalent atmospheric lifetimes ranging from hours to multiple days, control production of both inorganic and organic particle coatings, measure the chemical composition of gas- and condensed-phase organic compounds, measure the cloud condensation nuclei (CCN) activity of generated particles, and measure particle optical properties.

The proposed three-year laboratory research program will provide detailed information on relevant physiochemical properties of SOA as a function of oxidative processing, including interactions of gas-phase precursors with the condensed SOA. The SOA particles will be generated in conventional environmental chambers as well as in a more recently developed flow reactor that can produce SOA with high throughput over a wide range of simulated atmospheric conditions. The flow reactor enables controlled hydroxyl radical (OH) oxidation of atmospherically relevant gas phase and condensed-phase organic compounds. The residence time in the reactor is about two orders of magnitude shorter (minutes rather than days) and the OH concentration is two to three orders of magnitude higher than is attainable in environmental chambers.

This project will provide a more reliable database for modeling and predicting the role of aerosols in climate change and lead to a detailed understanding of how the chemical, physical and optical properties of carbonaceous aerosols are interconnected and how they change as a function of oxidative aging.