Atmospheric Chemistry Program Seminar

Optical Properties of Absorbing Organic Aerosol by Kevin Jansen, CU Boulder, ANYL 3rd year, Tolbert lab

"Until relatively recently, it has been assumed that organic aerosol only scatters light, thereby having a negative radiative forcing and global cooling effect. However, aerosol formed from the aqueous-phase reaction of small di-carbonyl compounds, such as glyoxal and methylglyoxal, with ammonium salts have the potential to form light-absorbing brown carbon (BrC) aerosol. Studies of BrC formation mechanisms and optical properties have been primarily preformed using bulk-aqueous solutions, although bulk-phase studies are not perfect simulations of reactions occurring within aerosol particles. In order to characterize BrC aerosol formed in the aerosol phase, we utilize Cavity ring-down (CRD) and Photoacoustic spectroscopies (PAS) to monitor the absorption and extinction of BrC aerosol formed from reactions of glyoxal and ammonium sulfate aerosol within reaction chamber. The PAS allows for the detection of BrC absorption even under conditions in which a few μg/m3 of weakly absorbing material is made. In addition, depending on the RH of the aerosol and if the aerosol was exposed to light, we observed differing losses in absorption by the BrC aerosol, which may indicate that BrC persists longer in the atmosphere than predicted from bulk phase experiments."