This work aims to improve understanding of how chemical complexity within the organic fraction of aerosols can directly influence the interaction of particles with light. A cavity ring-down aerosol extinction spectrometer and a photoacoustic spectrometer will be developed and used in the project. The extent to which heterogeneous processing of primary organic aerosol by hydroxyl (OH) radicals modulates the aerosol optical properties will be investigated, with an eye toward the role played by chemical composition and variability. Aerosols play a crucial role in regulating Earth's climate as well as providing surfaces for heterogeneous chemical reactions in the atmosphere. The direct effect of aerosols on climate is determined by their ability to scatter or absorb light, which depends critically on both their size and chemical composition.
Results from this project will be directly transferable to climate models by providing much needed new information on the optical properties of organic aerosol. Other broader impacts of this project will include the training of female graduate students and the participation of undergraduates in research. In addition, this project involves collaboration with Lawrence Berkeley National Laboratory and will bring University of California, Davis students into contact with researchers at a non-academic institution.
The scientific focus of this project has been on developing understanding of connections between the composition of atmospheric particles, especially the organic fraction, and their optical properties (e.g. absorption and scattering of light) and their affinity for water through detailed laboratory investigations. Atmospheric particles have strong impacts on global and regional climate that depend on their optical properties and ability to take up water. We have placed a particular focus on characterization of the effects of chemical processing on particle composition and properties. We have experimentally demonstrated for the first time that optical properties of organic particles are altered as they undergo simulated atmospheric ageing, and that these changes are linked to changes in their chemical composition. Chemical ageing can transform particles to have a greater propensity to absorb sunlight. We have refined relationships between organic particle composition and water affinity that can be used to develop more robust parameterizations for use in models. We have shown that chemical ageing generally causes particles to have a greater affinity for water. The extent to which particles take up water in the atmosphere in non-cloudy conditions affects the particle size and ability to scatter sunlight. We have developed the strongest evidence to date that the preference for certain types of organic compounds to be at the surface of growing droplets, rather than dissolved in the droplet bulk, has a substantial impact on the ability of those particles to grow into clouds. Finally, we have shown that variations in the composition of particles with particle size, and in particular the distribution of organic components, can have substantial control over the climate impacts of atmospheric particles. This is because the particles that are typically most important for cloud formation and those that are typically most important for direct scattering or absorption of solar radiation fall within different size regimes. The broader impacts of our studies have been realized through the furthering of relationships between a large research university and a large teaching-focused university that have provided opportunities for undergraduate research experiences. This project has also allowed for the training and development of two female environmental engineering students at the graduate level. Finally, the results from this Atmospheric Chemistry project have implications for the understanding of the impacts of atmospheric particulates on global and regional climate.
