Rebecca Washenfelder

washenfelder Absorption and Scattering by Atmospheric Aerosol

About the Presenter:

Rebecca Washenfelder is a scientist at NOAA in Boulder, Colorado. She received her Ph.D. in Environmental Science and Engineering with Paul Wennberg at Caltech in 2006. As a graduate student, she built an automated observatory to measure column concentrations of carbon dioxide and methane. Dr. Washenfelder began work at NOAA as a National Academies Postdoctoral Research Fellow in the Tropospheric Chemistry group, and has continued as a research scientist.

Dr. Washenfelder develops laboratory and field instruments to measure trace gases and aerosol using broadband cavity enhanced spectroscopy. BBCES is a sensitive and accurate technique that can achieve effective pathlengths of many kilometers in a cell with a physical length of 1 m. These optical cavities can be coupled to extremely high-power blue and ultraviolet LEDs. Currently, she is using these analytical methods to quantify the scattering and absorption by atmospheric aerosol particles.

Full Presentation:

Dr. Washenfelder declined to share her lecture online. Further information about her talk can be found by contacting the author.


Aerosol scattering and absorption are still among the largest uncertainties in quantifying global radiative forcing. Brown carbon has a wavelength-dependent absorption that increases in the UV spectral region, and its major atmospheric sources include biomass burning, anthropogenic combustion of fossil fuels, and secondary organic aerosol. The rural southeastern U.S. is influenced by high biogenic emissions and varying concentrations of biomass burning aerosol, making it an ideal place to compare the relative contributions of these two sources to the brown carbon absorption budget. During the Southern Oxidant and Aerosol Study in summer 2013, we deployed a new field instrument that uses cavity enhanced spectroscopy with a broadband light source to measure aerosol optical extinction as a function of wavelength. I will discuss laboratory and field results from this work.