Radiative properties of coated black carbon aerosols impacted by their microphysics

Abstract

Black carbon (BC) aerosols have substantial effects on the climate, whereas there still are significant uncertainties on coated BC radiative properties. Numerical investigations on radiative properties of polydisperse BC aggregates partially coated by non-absorbing organics, which are calculated by the exact multiple-sphere T-matrix method, are presented. The objective of our study is to evaluate the impacts of particle microphysics, including BC coating volume fraction, shell/core ratio, BC morphology, and size distribution, on partially coated BC radiative properties, as well as their absorption and scattering enhancements. Particle size distribution and shell/core ratio affect radiative properties of partially coated BC significantly, while BC coating volume fraction is an insensitive parameter. The absorption enhancement of BC particles due to partially coated by organics varies from ~1.0 to ~2.0, whereas their scattering enhancement can reach up to ~100. The BC coating volume fraction seems to be responsible for BC absorption enhancement, and with BC coating volume fraction becoming larger, the absorption enhancement becomes more sensitive to particle size distribution and shell/core ratio. However, the dependence of BC scattering enhancement on shell/core ratio is larger than size distribution and BC coating volume fraction, and the dependences of scattering enhancement to size distribution and BC coating volume fraction becomes stronger as shell/core ratio becomes larger. Our study gives a further understanding of the influences of particle microphysics on partially coated BC radiative properties, and it may be helpful for model and parameter simplifications.