Characterizing and Understanding Aerosol Optical Properties: CARES


Principal Investigator

Chris Cappa — University of California, Davis


Atmospheric aerosol particles play an important role in the Earth’s climate system through their ability to absorb and scatter solar radiation (the direct effect) and influence the properties of clouds (the indirect effect). Yet significant uncertainties remain in the representation of the aerosol direct effect within models and, as a result, the climate forcing due to atmospheric aerosols remains highly uncertain, thus hampering predictions of future climate change. Here, we are proposing to carry out detailed analyses of aerosol optical property measurements made during the 2010 Carbonaceous Aerosols and Radiative Effects Study (CARES) and, to a lesser extent, the 2012 ClearfLo campaign.
Our analysis will focus on the development of detailed, quantitative understanding of the relationships between aerosol optical properties and photochemical aging, particle composition and particle size. Specific analyses will focus on characterization and understanding of the observed variability in the aerosol hygroscopicity, the single scatter albedo, the wavelength-dependent absorption and contribution of “brown carbon” to the total absorption and the influence of coatings on black carbon absorption. In addition, multi-wavelength aerosol optical extinction coefficients obtained at both ground sites (one on the outskirts of Sacramento, CA, and one downwind in the foothills of the Sierra Nevada Mountains near Cool, CA) will be processed to obtain two key estimates of the aerosol size; the fine-mode fraction and effective optical fine-mode radius.
The general methodology to be used here is also commonly applied to remote-sensing measurements, and thus our application using in situ data can help to validate these remote methods. Results from this project will lead to advances in process-level understanding of what variables control the observed aerosol optical properties. Our analyses will utilize aerosol optical property data collected by the principal investigator and complementary measurements made by many other researchers as part of recently completed ARM field campaigns.