Effects of boundary layer particle formation on cloud droplet number and changes in cloud albedo from 1850 to 2000 School of Earth and Environment, University of Leeds, Leeds, UK
Received: 21 Oct 2008 – Published in Atmos. Chem. Phys. Discuss.: 27 Feb 2009 – Published: 25 Jan 2010Abstract. 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%.
Citation: Merikanto, J., Spracklen, D. V., Pringle, K. J., and Carslaw, K. S.: Effects of boundary layer particle formation on cloud droplet number and changes in cloud albedo from 1850 to 2000, Atmos. Chem. Phys., 10, 695-705, doi:10.5194/acp-10-695-2010, 2010.