Radiative and Hygroscopic Properties of Aerosols Containing Black Carbon at Various Mixing States

Title: Radiative and hygroscopic properties of aerosols containing black carbon at various mixing states Abstract There is a great degree of uncertainty about the role of soot or black carbon (BC) particles on the global climate, and it has been suggested that BC may be the second most important component of global warming. In atmosphere, BC particles interact with other aerosol particles and gas phase species, and exist mixed with organic and inorganic matters at various mixing states that include BC aggregates, randomly distributed BC particles in droplets, and BC particles residing in cores or shells of layered droplets. The radiative forcing ofBC depends on the mixing state, and the absorption of radiation by BC can increase significantly at certain mixing states. Currently, no experimental data exist on scattering and absorption by aerosols that contains BC in various mixing states. We propose to examine scattering and absorption characteristics as well as hygroscopic properties of aerosols containing black carbon (BC) mixed with hydrophilic and hydrophobic compounds at various mixing states. We will conduct experiments on single particles suspended in electrodynamic balances under controlled relative humidities. Particles of desired composition and characteristics (e.g., volumetrically distributed BC, or BC in cores or shells of layered droplets) will be generated by evaporation droplets of solution containing suspension of BC, vapor condensation, and electrostatic deposition of particles. We will apply techniques based on optical resonances, angle-dependent light scattering, and radiant heating to determine the complex refractive index of a particle. In addition, we will determine the deliquescence and crystallization humidities, as well as the water content of a particle at various relative humidities. We will develop models to predict optical properties of BC containing aerosols, and their dependence on the relative humidity. The results of this study will greatly improve the treatment of BC aerosols in climate models, and be useful in assessing the effects ofBC on solar radiation.