The Role of Water Vapor on Photo-bleaching of Organic Aerosol Particles

RACHEL O'BRIEN, Hongmin Yu, Alexandra Klodt, Laurel Nicks, Natalie Warren, Churchill Wilkinson, Marley Adamek, Monica Dibley, Christopher Lim, Carolyn Jordan, Bruce Anderson, Christopher Cappa, Jesse Kroll, Sergey Nizkorodov, University of Michigan

     Abstract Number: 262
     Working Group: Aerosol Physical Chemistry and Microphysics

Abstract
Organic aerosol particles can influence the climate through either directly absorbing or scattering solar radiation or by acting as nuclei for cloud droplets. Some aerosol particles are dominantly scattering while others contain organic molecules that can absorb solar radiation in the visible region, termed brown carbon (BrC). We still have large uncertainties in the magnitude of these climate effects and a better understanding of the possible removal processes is needed. One removal process is photolysis, where absorption of solar radiation leads to fragmentation of the organic molecules and the loss of particle mass and/or color. However, the photolysis rates and the overall extent of mass that can be removed via direct photolysis in laboratory experiments does not match what is used in models and often differs from ambient measurements. In particular, the role of water vapor, and its impact on the viscosity of the particles during photo-aging is an area of uncertainty. In addition, longer term photo-aging studies point to multi-generational products that can form in the particles, influencing their lifetime and behavior. Here, we will combine results from work in our lab looking at photolysis at different relative humidity values of biogenic secondary organic aerosol as well as BrC from both biomass burning organic aerosol and urban secondary organic aerosol to evaluate gaps in our ability to predict the longer-term fate of these particles in the atmosphere.