Organic Aerosol Dynamics: Single Particles and Modest Driving Forces

Carnegie Mellon University, Pittsburgh PA

Investigators

Abstract

In this project funded by the Environmental Chemical Sciences program in the Division of Chemistry of NSF, Professors Neil Donahue and Ryan Sullivan of the Carnegie Mellon University Center for Atmospheric Particle Studies will investigate the mixing of organic aerosols under conditions typically found in the atmosphere. Atmospheric particles consist of rich mixtures, often containing thousands of different organic compounds in a single particle. The way organic compounds form mixtures can profoundly influence how rapidly particles grow from tiny sizes (clusters of a few molecules) up to sizes that influence human health and climate (of order 100 nm in diameter) as well as their ultimate size. The research team also engages in outreach, combining the results of this research with broader issues of climate and health effects as part of the Science and Engineering Ambassadors program of the National Academy of Sciences. The team will probe the behavior of individual particles, either in isolation or in aerosol suspensions, to measure these key properties for both carefully prepared simple mixtures and rich mixtures consisting of secondary compounds formed via atmospheric oxidation of more volatile precursors. A key method will be to prepare two different aerosol suspensions in separate containers, often using isotopic labels (D or 13C) to ensure that the constituent mass spectra are completely distinct from one another. After combining the two suspensions, the researchers will then monitor the evolution of individual particle mass spectra while the constituents of the two populations interchange (if they do) via gas-phase exchange. In some cases variables such as chamber temperature and humidity will be varied. Both the rates of exchange and the ultimate stable mixing state will be key observables.