Numerically quantifying the spectral dependence of the absorption enhancement of partially-coated black carbon with complex microphysical properties

The absorption of black carbon (BC) will be enhanced after it is coated with other components, and the research on the enhancement of BC absorption has become a hot topic in climate research in recent years. Some studies have measured the enhancement of BC absorption in certain specific wavelengths, and these measurement results are often used for the analysis of absorption in other wavelengths as well. This work employs numerical methods to quantitatively study the impact of microphysical characteristics of BC with non-absorbing coating on its spectral characteristics of absorption enhancement. This study defines the absorption enhancement & Aring;ngstr & ouml;m exponent (EABSAE) to quantitatively describe the spectral characteristics of BC absorption enhancement. There are certain differences in the trends of absorption enhancement in different wavelengths with respect to microphysical characteristics, and EABSAE may deviate significantly from 0. The EABSAE of spherical BC usually varies between -2.5 and 2 in the wavelength range of 440-1064 nm. When considering the influence of complex morphology, the statistically average EABSAE of BC assembles with typical particle size distribution is roughly between -2 and 3. In the atmosphere, brown carbon (BrC) can mix with BC, which makes the EABSAE more complex. The EABSAE of BC coated with BrC can have a higher value. Therefore, an EABSAE value of at least 3 is required to prove the existence of BrC. In addition, the uncertainty in the calculation of absorption at other wavelengths was also evaluated in this work based on the absorption enhancement at a given wavelength.