Effects of boundary layer particle formation on cloud droplet number and changes in cloud albedo from 1850 to 2000

by J Merikanto, D V Spracklen, K J Pringle, K S Carslaw
Atmos. Chem. Physics ()


We use a global aerosol microphysics model to estimate the effect\nof particle formation through activation nucleation in the boundary\nlayer (BL) on cloud droplet number concentration (CDNC) on global\nand regional scales. The calculations are carried out for years 1850\nand 2000 using historical emissions inventories for primary particles\nand aerosol precursor gases. Predicted CDNC in 2000 are in good agreement\nwith in-situ observations when activation nucleation is included.\nWe find that BL particle formation increases global annual mean CDNC\nby approximately the same relative amount in both years (16.0% in\n1850 and 13.5% in 2000). As a result, global mean changes in cloud\nalbedo are similar with and without BL particle formation. However,\nthere are substantial regional effects of up to 50% enhancement\nor suppression of the 1850-2000 albedo change. Over most modern-day\npolluted northern hemisphere regions, including BL particle formation\nscheme suppresses the 1850-2000 increase in CDNC and cloud albedo\nbecause BL particle formation is already large in 1850. Over the\nArctic the albedo change is suppressed by 23% in the annual mean\nand by 43% in summer when BL particle formation is taken into account.\nThe albedo change of the persistent stratocumulus cloud deck west\nof Chile is enhanced by 49%.

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