The Second Pallas
Cloud Experiment (Second PaCE) was conducted at the Pallas-Sodankylä Global
Atmosphere Watch (GAW) station in northern Finland from 16 September to 6
October 2005. Measured parameters included aerosol number size distribution,
aerosol chemical composition, aerosol hygroscopic growth factor, cloud droplet
number size distribution and meteorological parameters. Air mass back
trajectories were also calculated. The particulate volume and the inorganic
fraction (IO) of particulate mass depended strongly on the air-mass history:
central European air masses contain much more particulate matter and have higher
IO than marine air masses. The hygroscopic growth factor of particles was
positively correlated with the IO. Aerosol activation into cloud droplets was
studied for accumulation mode particles ( d _p > 100 nm). The
activation of these particles did not show clear dependency on the number
concentration of accumulation mode particles or on IO. These two parameters were
positively correlated and their effects on the particle activation could not be
separated.