Aerosol particles affect climate by changing the Earth’s atmospheric radiative balance. These climate effects are somewhat smaller than that of the greenhouse gases, generally opposite in sign and much more uncertain. The high uncertainties are due to the current, inadequate representation of aerosol interactions with solar radiation and clouds These interactions are complicated due to the complex composition, morphology, and size of particles, and the evolution of these properties throughout their atmospheric lifetimes. Organic compounds are found on almost all atmospheric particles through secondary organic aerosol (SOA) formation processes and may significantly influence particle behavior. However, the effect of SOA on climate is still not well understood. Modeling procedures have not been adequate for predicting climate forcing by SOA because of major gaps in our understanding of atmospheric processes that affect SOA formation, chemical composition, hygroscopicity, and optical properties.

            Understanding the fundamental aerosol life cycle (from nucleation to growth to CCN formation) is required to predict aerosol number and loading in the current, past and future atmospheres, each with variable natural and anthropogenic emissions along with changing anthropogenic activity and land use. For SOA this requires investigation of complex molecular species over a range of precursors and simulated atmospheric oxidation conditions. Environmental chamber experiments have to date been the source of most laboratory SOA data used in atmospheric models, but chamber methods are limited in their ability to produce highly oxygenated SOA characteristic of aged atmospheric organic aerosol. Recently developed aerosol flow reactors can simulate the full range of integrated atmospheric oxidant exposures. Initial studies over a limited range have shown that these reactors simulate atmospheric aerosol chemistry. However, a broader validation of the method is required.

            We conducted a series of studies designed to facilitate more accurate predictions of SOA climate forcing by conducting laboratory measurements that reduce uncertainties related to the modeling of SOA formation, growth and atmospherically important properties. Toward this goal, we performed a uniquely detailed molecular characterization of SOA production utilizing state-of-the-art mass spectrometric techniques that can
measure oxidized organic species in both the gas
and particle phases. These molecular ion signatures identify the precursor/oxidant process, connected to aerosol growth/condensation. We coupled mass spectrometer measurements to a high-throughput aerosol flow reactor to facilitate efficient investigation of many chemical
systems, including aerosols produced from mixtures of biogenic VOCs with anthropogenic VOCs, SO₂, and NO_x. We also provide a method for determining the potential for wall effects on the SOA chemistry occurring in environmental chambers and oxidative flow reactors and show how chambers could be made to better simulate atmospheric SOA chemistry.

Results from our experiments are summarized in several manuscripts that have been published or submitted to refereed journals. In addition, the research team has presented the work at approximately ten scientific meetings as poster or platform presentations. Information disseminated in our manuscripts is being used by researchers in the field of atmospheric chemistry. This work provided and continues to provide key parameters needed to understand the role of aerosols in atmospheric chemistry and in global climate. The work related to organic aerosols is providing new basic information about interactions and transformations of these important pollutants.            

Last Modified: 09/01/2019
Modified by: William H Brune