Evaluating the impacts of cloud processing on resuspended aerosol
particles after cloud evaporation using a particle-resolved model
Abstract
Aerosol particles undergo physical and chemical changes during cloud
processes. In this work, we quantified the changes in aerosol mixing
state using a particle-resolved model. To this end, we coupled the
particle-resolved aerosol model PartMC-MOSAIC with the aqueous chemistry
module CAPRAM 2.4 and designed cloud parcel simulations that mimicked
several cloud cycles that a particle population may be exposed to in an
urban environment. Aqueous-phase chemistry during these cloud cycles
affected aerosol mixing state and the particles’ potential to act as
cloud condensation nuclei (CCN) significantly, with the largest
differences after the first cloud cycle. The mean size and total dry
mass of the population increased by 24% and 219%, respectively, after
the first cycle, while the increments were only 5% and 38% after the
fourth cycle. The formation of ammonium sulfate and nitrate were
responsible for those changes. Cloud processing increased the internally
mixed state of all particle populations, with the mixing state index
increasing from 50 to 83 percentage points after four cloud cycles. The
CCN concentrations for supersaturations lower than 0.23% increased. For
example, for supersaturation levels of 0.02%, the CCN concentration
increased from 25 to 547 cm-3. Brownian coagulation
led to an increase of the CCN/CN ratio for supersaturation levels higher
than 0.2%. The ratio increased by 4.1% at the supersaturation level
0.5%. Total number concentration and CCN concentration decreased by
5.9% and 1.7%, respectively, when Brownian coagulation is considered.
These findings highlight the complex influence of cloud processing on
particle properties.