Aerosol particles were sampled at 18 m above sea level through a heated mast (Bates et al., 1998, ACE-1 JGR Special Issue). The mast extended 6 m above the aerosol measurement container and was capped with a rotating cone-shaped inlet nozzle that was positioned into the relative wind. Air was pulled through this 5 cm diameter inlet nozzle at 1 m3 min-1 and down the 20 cm diameter mast. The lower 1.5 m of the mast were heated to dry the aerosol to a relative humidity (RH) of 40 to 50%. Fifteen 1.9 cm diameter conductive tubes extending into this heated zone were used to isokinetically subsample the air stream for the various aerosol sizing instruments and impactors at flows of 30 l min-1. Comparisons of the total particle count (Dp > 5 nm) during intercomparisons with the NCAR C-130 agreed to within 20% suggesting minimal loss of particles in the inlet system.
One of the 15 1.9 cm diameter tubes was used to supply ambient air to the UDMPS, DMPS and TSI 3025 particle counter. The total particle number concentration data are reported in other files. The two DMSPs were located just outside the humidity controlled box at the base of the mast. The UDMPS was a Vienna short column instrument connected to a TSI 3025 particle counter operating with a negative particle charge. Data were collected in 9 size bins. The UDMPS operated with an aerosol flow rate of 1.5 L/min and a sheath air flow rate of 10 L/min on Leg 1 (Seattle to Hobart) and 20 L/min on Leg 2 (intensive). The DMPS was a TSI long column instruments connected to a TSI 3010 particle counter operating with a positive particle charge. Data were collected in 17 size bins. The DMPS operated with an aerosol flow rate of 1 L/min and a sheath air flow rate of 5 L/min. The relative humidity of the sheath air was dry resulting in a measurement RH in the DMPSs of approximately 10%. Number size distributions were collected every 10 minutes.
The data were filtered to eliminate periods of calibration and instrument malfunction and periods of ship contamination (based on relative wind and high CN counts). The filtered mobility distributions from the DMPSs were inverted to a number distribution by assuming a Fuchs-Boltzman charge distribution resulted from the Kr85 charge neutralizer. The data were corrected for diffusional losses (Covert et al., 1997) and size dependent counting efficiencies (Wiedensohler et al., 1997) based on pre-ACE-1 intercalibration exercises. The inverted ten minute data were averaged into 30 minute periods centered on the hour and half-hour.
one of the 15 1.9 cm diameter tubes was used to supply ambient air to the
APS located just outside the humidity controlled box at the base of the
mast. The relative humidity of at the instrument was below the efflorescence
point of sea salt (approximately 45%RH, Tang et al., 1997). The data reported
here are in 26 size bins from 0.835 to 5.0 micrometers. Data at diameters
larger than 5 mm
were discarded due to interferences from phantom counts and uncertainties
in large particle collection efficiencies. Number size distributions were
collected every 10 minutes.
Covert, D., A. Wiedensohler, and L.M. Russell, Particle charging and transmission efficiencies of aerosol charge neutralizers. Aerosol Sci. and Technol., 27, 206-214, 1997.
Tang, I.N., A.C. Tridico, and K.H. Fung, Thermodynatmic and optical properties of sea salt aerosols. J. Geophys. Res., 102, 23,269-23,275, 1997.
Wiedensohler, A., D. Orsini, D.S. Covert, D. Coffmann, W. Cantrell, M. Havlicek, F.J. Brechtel, L.M. Russell, R.J. Weber, J. Gras, J.G. Hudson, and M. Litchy, Intercomparison study of size dependent counting efficiency of 26 condensation particle counters. Aerosol Sci. and Technol., 27, 224-242, 1997.
U.S.Dept of Commerce / NOAA / OAR / PMEL / Atmospheric Chemistry