The School of Earth and Atmospheric Sciences Presents Dr. Pengfei Liu, Harvard University

Climate-Relevant Properties of Atmospheric Organic Aerosols

Atmospheric aerosol particles are ubiquitous in the atmosphere and exert a significant influence on regional and global climate. The aerosol particles affect climate by scattering and absorbing solar radiation, as well as by serving as nuclei for cloud formation. A large fraction of the sub-micrometer particle mass consists of secondary organic material, produced by atmospheric oxidation of volatile organic compounds. The properties of secondary organic material remain uncertain given the diversity of precursor types and oxidation conditions.

Further, there is limited understanding about how organic aerosol particles interact with surrounding gas molecules. These interactions can affect the production and chemical aging of organic particles in the atmosphere. Here, I developed novel thin-film-based experimental approaches to characterize the climate-relevant properties of secondary organic material.

These properties include the optical constants, phase states, volatility, and hygroscopicity. These new measurements can be used to answer the following scientific questions: 1) How organic particles interact with solar radiation? 2) How do organic particles interact with water vapor and serve as cloud condensation nuclei? 3) How does the phase state of organic particles influence the gas-particle partitioning of semi-volatile species and multiphase reactions rates?

The results highlight different properties observed between secondary organic materials derived from anthropogenic and biogenic sources. These differences should be considered in the modeling of atmospheric organic aerosols.