AAAR 31st Annual Conference
October 8-12, 2012
Hyatt Regency Minneapolis
Minneapolis, Minnesota, USA
Abstract View
Particle-Resolved Simulations on the Effects of Black Carbon Mixing State on Cloud Droplet Number Concentration and Radiative Forcing
JOSEPH CHING, Nicole Riemer, Matthew West, University of Illinois at Urbana-Champaign
Abstract Number: 600 Working Group: Aerosols, Clouds, and Climate
Abstract The climate impacts of black-carbon-containing particles are complex. On the one hand particles of this type absorb solar radiation (the direct effect), on the other hand they may act as cloud condensation nuclei (CCN), which in turn form cloud droplets and hence reflect solar radiation (the first indirect effect). The latter impact is further complicated since the potential of black-carbon-containing particles to form cloud droplets does not only depend on the physico-chemical properties of the black carbon particles. It also depends on the other particles present in the population, which all compete for water vapor, and on environmental parameters such as the updraft speed.
In this study we investigate how the aerosol mixing state impacts the cloud-forming ability of black-carbon-containing particles. We employ a two-step approach by using the particle-resolved aerosol model PartMC-MOSAIC in conjunction with a particle-resolved cloud parcel model. First, we use PartMC-MOSAIC to simulate a suite of 2-day evolutions of the aerosol population in an urban plume, varying the emission rates of black-carbon-containing particles and the concentration of background particles to cover a wide range of atmospherically relevant conditions. We then use the hourly output of these particle-resolved simulations as input to a particle-resolved cloud parcel model to study the activation and the condensational growth of the CCN. With this method we explicitly resolve the composition of individual particles and cloud droplets in a given population of different types of aerosol particles, and accurately track their evolution due to emission, dilution, condensation and coagulation. We investigate the impact of black carbon mixing state on cloud droplet number concentration (CDNC) by comparing the CDNC obtained from a particle-resolved population to that obtained from its derived counterpart in which particles are completely internally mixed. We discuss the relevance of accounting for aerosol mixing state when estimating the radiative forcing.