Aerosol size distributions measured at the South Pole during ISCAT

Aerosol physical size distributions were measured at the South Pole during December 1998 and December 2000 as part of the ISCAT program. The size ranges covered by these measurements were 3 to 250 nm in 1998 and 3 nm–2 μm in 2000. “Typical background aerosols” measured during both periods were similar. Total aerosol number concentrations ranged from 100 to 300 cm−3 with occasional spikes as high as 10,000 cm−3. We believe the spikes were due to local emissions. The number mean size of background aerosols ranged from 50 to 70 nm, and total aerosol surface area concentrations were 2.8±0.4 μm2 cm−3. Aerosols measured in December 2000 were cleanly separated into “low volume” and “high volume” periods. During the low-volume periods, volume concentrations were 0.07±0.01 μm3cm−3 with a volume mean diameter of 0.27±0.05 μm, and these volume concentrations were mostly within a factor two of values that would be expected based on reconstructed mass from particulate chemical composition. Volume concentrations during the “high volume” periods exceed levels that can be explained from aerosol chemistry and calculated light-scattering coefficients exceed values that have been recorded historically. We have been unable to identify why this might have occurred. We observed one 4-h event on December 15, 2000 during which nanoparticles grew slowly from 3.0 to 3.6 nm.We believe these particles had recently been formed by nucleation. Because this occurred during a period of stagnation, it is possible that this event was associated with local emissions.