We use a global aerosol microphysics model to estimate the effect
of particle formation through activation nucleation in the boundary
layer (BL) on cloud droplet number concentration (CDNC) on global
and regional scales. The calculations are carried out for years 1850
and 2000 using historical emissions inventories for primary particles
and aerosol precursor gases. Predicted CDNC in 2000 are in good agreement
with in-situ observations when activation nucleation is included.
We find that BL particle formation increases global annual mean CDNC
by approximately the same relative amount in both years (16.0% in
1850 and 13.5% in 2000). As a result, global mean changes in cloud
albedo are similar with and without BL particle formation. However,
there are substantial regional effects of up to 50% enhancement
or suppression of the 1850-2000 albedo change. Over most modern-day
polluted northern hemisphere regions, including BL particle formation
scheme suppresses the 1850-2000 increase in CDNC and cloud albedo
because BL particle formation is already large in 1850. Over the
Arctic the albedo change is suppressed by 23% in the annual mean
and by 43% in summer when BL particle formation is taken into account.
The albedo change of the persistent stratocumulus cloud deck west
of Chile is enhanced by 49%.
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