DATE/TIME: Friday, December 1, 2023, 2:30 pm
Ogochukwu Enekwizu
Brookhaven National Laboratory
The Activation Properties of Fresh and Aged Black Carbon Particles from Biomass Burning
Black carbon (BC) particles affect climate directly through the absorption of solar radiation and indirectly by changing cloud properties such as cloud amount and lifetime. An abundant source of BC is biomass burn (BB) events (i.e., wildfires), which concurrently release copious amounts of condensable organic vapors that form thick coatings that encapsulate the BC. The coatings increase the hydrophilicity of the otherwise hydrophobic BC particles while at the same time increase the particle size, both of which enhance the ability of these particles to act as cloud condensation nuclei (CCN) and affect their optical properties. Due to the complex interplay between hydrophilic properties of the coating and the hydrophobic properties of the BC “core”, along with the particle size, better quantification of the hygroscopic properties for this important class of particle will improve our understanding and representation of the direct and indirect climatic forcing contributions by these particles. In this seminar, I will discuss the CCN activity of pure and thickly coated BC surrogate particles determined by laboratory measurements under typical atmospheric supersaturations using levoglucosan, a known tracer for BB, as a proxy for fresh organic coating and oleic acid as a surrogate for aged organic coating, as a function of coating thickness for different core (i.e., BC) mobility diameters. Additionally, experimental results are used to derive the hygroscopicity parameter (κ) of the BC core and coatings. The limiting cases of fresh and aged organic coatings, which span the range of coating ages, are used to investigate the activation behavior of an ensemble BC particle population consisting of particles with different core diameters and different coating thicknesses and how activation, in turn, affects the aerosol optical properties. The findings presented provide a critical fundamental-level understanding of aerosol-cloud interactions for this important class of particles.
Seminar Host:
Mark Miller
Atmospheric Science Group, Department of Environmental Sciences, Rutgers University