Airborne sampling of aerosol particles: Comparison between surface sampling at Christmas Island and P-3 sampling during

[1] Bulk aerosol sampling of soluble ionic compounds from the NASAWallops Island P-3 aircraft and a tower on Christmas Island during PEM-Tropics B provides an opportunity to assess the magnitude of particle losses in the University of New Hampshire airborne bulk aerosol sampling system. We find that most aerosol-associated ions decrease strongly with height above the sea surface, making direct comparisons between mixing ratios at 30 m on the tower and the lowest flight level of the P-3 (150 m) open to interpretation. Theoretical considerations suggest that vertical gradients of sea-salt aerosol particles should show exponential decreases with height. Observed gradients of Na+ and Mg2+, combining the tower observations with P-3 samples collected below 1 km, are well described by exponential decreases (r values of 0.88 and 0.87, respectively), though the curve fit underestimates average mixing ratios at the surface by 25%. Cascade impactor samples collected on the tower show that>99%of theNa+ andMg2+mass is on supermicron particles, 65 % is in the 1–6 micron range, and just 20 % resides on particles with diameters larger than 9 microns. These results indicate that our airborne aerosol sampling probes must be passing particles up to at least 6micronswith high efficiency.We also observed that nss SO