Our work on the multi step processing of BC-BrC, which utilized
condensation of H2SO4 and subsequent neutralization and hydration,
provides an attempt to mimic the real sequence of atmospheric
aging events and to investigate the corresponding
alteration in BC-BrC's light absorption, as shown in Fig. 6. Our study
suggests that surface reactions can modify the mixing state and morphology of BC-BrC. The restructuring of BC-BrC largely determines
the light absorption ability at low humidity even if
neutralization of SA-coating by NH3 or (CH3CH2)3N causes mass
growth of non refractory coating. Heating experiments could not
verify he restructuring of BC-BrC induced by condensation of sulfuric
acid because of the formation of refractory sulfur-containing
species, while it was evident that neutralization of NH3 or
(CH3CH2)3N with condensed H2SO4 act to compact the BC inclusion.
Meanwhile, ammonium sulfate coating originated from reaction
between SA and NH3 on the surface was evidenced to be nonuniform,
which was different from the coreeshell configuration and
correspondingly hindered the lensing effect. In addition, the effect
of high relative humidity in the evolution of internally mixed BC
and/or BrC has been investigated in this work. Above the deliquescence
relative humidity, hydrophilic sulfate coating will exert
primarily lensing effect that enhances absorption although
shielding effect is also occurring.