Tim Bates, bates@pmel.noaa.gov, May 14, 1998 206-526-6248, fax 206-526-6744 Derek Coffman, derek@pmel.noaa.gov, May 14, 1998 206-526-6574, fax 206-526-6744 R/V Discoverer ACE-1 NOAA-PMEL Short Description: Corrected shipboard particle number size distributions (30 minute averages). UDMPS/DMPS data at measurement RH (10%) and APS data corrected to geometric diameters and shifted to dry RH (10%) 22 data files, Leg 2 (intensive) Keywords: UDMPS, DMPS, APS, Corrected, Measurement RH Version 2 - replacing "Discoverer Aerosol Size Distributions Data (Quinn)" Full Description of data set: DOY: DOY is decimal day of year such that DOY 32.5 is 12 noon UTC on 1 February. The DOY value is for the center of the 30 minute averaging period. PMEL particle number size distributions aboard the R/V Discoverer: Aerosol particles were sampled at 18 m above sea level through a heated mast. 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 40-50%. Fifteen 1.9 cm diameter conductive tubes extending into this heated zone were used to isokinetically subsample the air stream for the various aerosol instruments at flows of 30 l min-1. Comparisons of the total particle count (Dp > 3 nm) during intercomparisons with the NCAR C-130 during ACE-1 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. 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 averaged 40%. 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 ten minute data were averaged into 30 minute periods centered on the hour and half-hour. The value of -99 is assigned to any 30 minute period without data. Data are reported in geometric diameter (micrometers) in units of dN/dlogDp (cm3) at a "dry" RH of 10%. The mobility distributions from the UDMPS/DMPS 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 APS data have been converted from aerodynamic diameters to geometric diameters using calculated densities and the diameters shifted to "dry" sizes using a calculated growth factor. The densities used to convert the diameters were calculated using a thermodynamic equilibrium model (AeRho). AeRho uses Ion Chromatograph data from impactor measurements and the measured RH to determine the densities for each impactor stage. These calculations are based on the assumption that the aerosols were composed of two externally mixed fractions: a non-sea salt fraction and a sea salt fraction. Thus, for each impactor sample, a density distribution is calculated for each assumed aerosol mixture. For more information regarding the model see Quinn and Coffman, 1998. For this data set, it is assumed that the APS data are composed entirely of sea salt aerosol so the calculated densities for the sea salt mixture were used to convert the diameters. To shift the APS data to "dry" sizes, a measured growth factor for sea salt was applied to the data. This growth factor used was 1.5 based on an average of H-TDMA measurements from 10% to 50% (Berg et al., 1998). The UDMPS data reported here are in 9 size bins with geometric diameters ranging from 0.005 to 0.0286 micrometers. These size bins are different from those reported in Leg 2 because of the change in sheath and excess flow. The DMPS data reported here are in 17 size bins with geometric diameters ranging from 0.20 to .057 micrometers. The APS data reported here are in 26 size bins with original aerodynamic diameters ranging from 0.835 to 5.0 micrometers. Data at diameters larger than 5 um were discarded due to interferences from phantom counts and uncertainties in large particle collection efficiencies. The data have been separated into 22 separate files that correspond to the impactor sampling periods. This was done in order to use the calculated densities from each of these periods. The same UDMPS/DMPS and APS data are also available in the ACE-1 data archive in an uncorrected format. References: Berg, O. H., E. Swietlicki, and R. Krejci, Hygroscopic growth of aerosol particles in the marine boundary layer over the Pacific and Southern Oceans during ACE-1, J. Geophys. Res., in press, 1998. 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. Quinn, P. K., D. J. Coffman, Local closure during ACE 1: Aerosol mass concentration and scattering and backscattering coefficients. J. Geophys. Res., in-press, 1998. 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.