Toward the Minimal Representation of Particle Physical and Chemical Properties for Modeling Absorption By Black Carbon

Absorption by a particle containing black carbon (BC) depends on its constituent aerosol species and the arrangement of those species within the particle. BC-containing particles exhibit tremendous variation in their chemical composition and internal morphology, but these particle-scale properties are not fully resolved in large-scale chemical transport models. Instead, models approximate the distribution in components among individual particles, for example by assuming fully internal or fully external mixtures, and approximate the arrangement of those components within each particle, for example by applying the core-shell approximation.  By combining PartMC-MOSAIC particle-resolved model simulations with single-particle soot photometer measurements, we evaluate the extent to which particle composition and morphology must be resolved in order to model BC absorption. We show that, while absorption by BC at the particle-level is sensitive to the treatment of particles’ internal morphology, internal morphology plays a much smaller role in the total absorption by populations of BC-containing particles. On the other hand, population-level absorption is highly sensitive to model representations of particle composition. By identifying the physical and chemical properties to which absorption is most sensitive, this study guides the development of reduced models for simulating aerosol radiative effects.