Seminar: Dr. Ulrich Krieger
Please join us as we welcome Dr. Ulrich Krieger, a Senior Scientist from the聽Institute for Atmospheric and Climate Science in the聽聽Department of Environmental Systems Science at聽ETH Zurich,聽for a聽seminar聽titled "Effect of particle morphology on the absorption cross section of aerosol particles containing brown or black carbon".聽Coffee will be served.
Abstract
While it is well known that absorption by light absorbing carbon increases when the carbon is internally mixed with other material (e.g. Bond et al. 2013), the magnitude of this enhancement is still under debate (Cappa et al., 2013). Attributing the large variability of measured absorption enhancement relies on an appropriate representation of carbon morphology and mixing with other materials (Scarnato et al., 2013).
Here we investigate in particular how liquid-liquid phase separation (LLPS) influences the absorption cross section of particles containing absorbing, molecular carbon (鈥渂rown carbon鈥�) as well as black carbon aggregates.
I will first discuss the molecular absorber case. I will show experimental evidence that a core shell morphology is the most prevalent morphology for phase separated atmospheric aerosol and that the molecular absorbers are in the organic phase after LLPS. I will compare calculated absorption efficiencies for homogeneous particles and phase separated particles for different scenarios, i.e. different volume mixing ratios and concentrations of the molecular absorber.
Recently, we showed that also black carbon (BC) preferentially segregates into the organic phase upon LLPS in micron size particles (Brunamonti et al. 2015), resulting in an 鈥渋nverted core-shell structure鈥�, in which a transparent aqueous core is surrounded by a BC-containing absorbing shell. In the Brunamonti et al. study, the radiative effect for accumulation size particles was estimated assuming the BC-absorption to be volume mixed within the shell. I will compare this with a more realistic treatment of the black carbon as fractal aggregate and also study configurations in which the black carbon is only partially embedded in the organic liquid phase.