Chemical and optical changes to black carbon during aging

Black carbon (BC) is the second most important contributor to global warming. Due to its short atmospheric lifetime (~days), reductions in BC may be one of the fastest mechanisms to reduce warming. Recent field measurements indicate that BC is a chemically and physically dynamic atmospheric constituent, suggesting that radiative forcing effects of BC may evolve quickly (on the timescale of hours) in the atmosphere. The specifics of how (and even if) the radiative forcing potential of BC changes as it ages, however, is currently under debate, thus leading to significant uncertainties on the magnitude of BC contribution to radiative forcing. We attempt to help constrain this uncertainty using a series of laboratory measurements that systematically study the aging process of BC. These laboratory measurements are carried out using a photo-oxidation chamber and an extensive suite of measurements including an Aerodyne Soot-Particle Aerosol Mass Spectrometer (SP-AMS) and measurements of aerosol optical properties. Using this instrument suite, we characterize how the chemical and optical properties of BC change as it is aged heterogeneously (by OH and ozone) and as it is coated by organic material.