This research includes the development of a new mobile instrument for providing data on the column absorption of infrared radiation by hydrocarbons in the atmosphere, a process that can lead to an atmospheric warming. The Principal Investigator of the project also has been invited to visit the Paul-Scherrer Institute in Switzerland to design a series of experiments at the CLOUD chamber facility at CERN. This facility will enable him to study the formation of secondary organic aerosol (SOA) in the atmosphere under varying conditions of ambient temperature and pressure. It is important to understand the mechanisms that lead to the fast formation and growth of secondary organic aerosol since they are important in predicting air quality and climate change.
The proposed CLOUD chamber experiments will focus on the 'salting-in' effect as a mechanism for explaining accelerated nanoparticle growth rates. In the case of glyoxal, 'salting-in' consists of the displacement of water molecules from the hydration shell of sulfate ions by hydrated glyoxal molecules. Preliminary studies show efficient growth from glyoxal at relative humidity (RH) of up to 20% for highly acidic nanoclusters. However, there are currently no experimental data available at RH above 20% and for neutral nanoclusters, where the multiphase chemistry is expected to proceed via different pathways. The proposed research will address the following questions related to the formation of SOA (associated with glyoxal) in the atmosphere: (1) What is the 'threshold cluster size' at which glyoxal begins to assists with the stabilization/growth of clusters; and (2) How does the growth rate of stable clusters depend on relative humidity and pH? The 'salting-in' mechanism has been incorporated in an atmospheric model to successfully explain the fast formation of SOA from glyoxal that was observed in a recent NSF-supported field campaign to study air pollution in Mexico City.
The development of the mobile Solar Occultation Flux instrument and the acquisition of new expertise for IR retrievals from the instrument will offer a novel way to better quantify atmospheric composition and changes in composition. The experiments at the CLOUD chamber may result in transformative research on the mechanisms for formation and growth of secondary organic aerosol. This research is funded through the EArly-concept Grants for Exploratory Research (EAGER) program.
