Seminar: Dr. Chris Hennigan | UMBC
In-Person PHYS 401
Location
Physics : 401
Date & Time
September 20, 2023, 11:00 am – 12:00 pm
Description
TITLE: The Chemistry of Brown Carbon Aerosols in the Atmosphere: Influences on Radiative Forcing
ABSTRACT: Light-absorbing organic species present in aerosols, collectively called brown carbon (BrC), contribute important but highly uncertain effects on climate. Among absorbing species present in aerosols, BrC is unique because it is both emitted directly into the atmosphere (primary BrC) and formed from gas- and aqueous-phase reactions (secondary BrC). It is also unique because reactions initiated by oxidants and UV light can rapidly transform chromophores into non-absorbing (or more weakly absorbing) species in a process called bleaching. Clouds likely represent a significant medium for the production of secondary BrC and for a variety of bleaching reactions, though the relative importance of formation and loss processes in clouds is unknown at present. The acidity (or pH) of atmospheric particles and clouds affects the optical properties of BrC and bleaching rates, although the link between pH and BrC is yet another uncertainty in attempts to constrain its climate forcing effects. Given the wide variability of pH in the atmosphere (pH in particles and clouds ranges from -1 to 8), the optical properties of BrC and its bleaching behavior are expected to vary significantly in the atmosphere, as well. This talk will explore results from our study measuring BrC in cloud water samples from Whiteface Mountain, NY. We focus on the pH-dependence of BrC optical properties and how those properties are affected by different sources and atmospheric processes, ultimately providing guidance to better constrain the radiative forcing of BrC.
ABSTRACT: Light-absorbing organic species present in aerosols, collectively called brown carbon (BrC), contribute important but highly uncertain effects on climate. Among absorbing species present in aerosols, BrC is unique because it is both emitted directly into the atmosphere (primary BrC) and formed from gas- and aqueous-phase reactions (secondary BrC). It is also unique because reactions initiated by oxidants and UV light can rapidly transform chromophores into non-absorbing (or more weakly absorbing) species in a process called bleaching. Clouds likely represent a significant medium for the production of secondary BrC and for a variety of bleaching reactions, though the relative importance of formation and loss processes in clouds is unknown at present. The acidity (or pH) of atmospheric particles and clouds affects the optical properties of BrC and bleaching rates, although the link between pH and BrC is yet another uncertainty in attempts to constrain its climate forcing effects. Given the wide variability of pH in the atmosphere (pH in particles and clouds ranges from -1 to 8), the optical properties of BrC and its bleaching behavior are expected to vary significantly in the atmosphere, as well. This talk will explore results from our study measuring BrC in cloud water samples from Whiteface Mountain, NY. We focus on the pH-dependence of BrC optical properties and how those properties are affected by different sources and atmospheric processes, ultimately providing guidance to better constrain the radiative forcing of BrC.
