Analytical Chemistry Seminar: Dr. Eleanor Browne
Jointly sponsored by the Department of Chemistry and Biochemistry, CIRES, and the Environmental Program
Chemical Changes to Light Absorbing Carbonaceous Aerosol with Oxidative Aging
Dr. Eleanor Browne, MIT
Light absorbing carbonaceous aerosol (LAC) is one of only two atmospheric components that both degrade air quality and cause climate warming. Due to the short atmospheric lifetime (~days-weeks) of LAC, there has been considerable recent interest in quantifying the climate and health impacts of LAC and developing mitigation strategies that will simultaneously improve climate and human health. Despite this recent interest, large uncertainties in the quantification of LAC's climate impact remain. In part this is due to the poorly characterized influence of 'aging', the complex atmospheric processes that alter the chemical and physical properties of aerosol over their lifetime.
In this talk, I discuss experiments using vacuum ultraviolet (VUV) ionization-high resolution aerosol mass spectrometry to quantify the kinetics and chemical composition changes to LAC (both black and brown carbon) upon oxidation. In brief, I find that heterogeneous oxidation by OH of the aliphatic compounds present on the surface of black carbon particles occurs quickly (lifetime of ~1 day) and produces oxygenated hydrocarbons. I also present results for the aging of brown carbon generated from the smoldering of pine needles. The primary aerosol emitted from smoldering is highly oxygenated and when it ages in the presence of the gaseous smoldering emissions, a chemically distinct secondary organic aerosol component forms. These results show that LAC undergoes substantial chemical changes on the timescale of a day. Since the chemical changes described here likely have important impacts on the climate-relevant properties of LAC (such as light absorption and hygroscopicity), further quantification of these aging mechanisms and timescales is needed in order to accurately estimate the climate effects of LAC.