Title: R.H. Brown Aerosol Number Size Distributions (combined 55%RH DMPS-APS data, Aerosols99 and INDOEX) Contact: Timothy S Bates OCRD NOAA/PMEL 7600 Sand Point Way NE Seattle, WA 98115 USA Phone: 206-526-6248 Fax: 206-526-6744 E-Mail Address: bates@pmel.noaa.gov Or Derek Coffman NOAA/PMEL 7600 Sand Point Way NE Seattle, WA 98115 USA 206-526-6574 206-526-6790 E-Mail Address: derek@pmel.noaa.gov Short Description: R/V Ronald H. Brown Aerosols99 and INDOEX combined particle number size distributions (30- minute averages). DMPS and APS data at wet measurement RH (approximately 55%). APS data corrected to geometric diameters. Measurements made by IfT (Wiedensohler) DMPS data inverted by IfT (Wiedensohler) Data reduced, analyzed and combined by PMEL 38 data files (Norfolk, VA to Cape Town, SA) 14 data files (Cape Town, SA to Port Louis, Mauritius) 48 data files (INDOEX) Keywords: DMPS, APS, wet RH Version 1 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. Latitude and Longitude: Position of the ship at the center of the averaging period in decimal degrees from the PMEL GPS unit. Particle number size distributions aboard the R/V Ronald H. Brown: Aerosol particles were sampled at 18 m above sea level through a heated mast. The mast extended 5 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 55%. Fifteen 1.9 cm diameter conductive tubes extending into this heated zone were used to subsample the air stream for the various aerosol instruments at flows of 30 l min-1. One of the fifteen 1.9 cm diameter tubes was used to supply ambient air to the DMPS. The DMSP was located inside the humidity-controlled box at the base of the mast. The DMPS was a University of Vienna (Reischle) medium column connected to a TSI 3010 particle counter operating with a negative particle charge. Data were collected in 17 size bins. The DMPS operated with an aerosol flow rate of 0.5 L/min and a sheath air flow rate of 5 L/min. The sheath air was humidified to 55% RH. Mobility distributions were collected every 15-minutes. The mobility distributions from the 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 and size dependent counting efficiencies based on pre-ACE-2 intercalibration exercises at IfT. The DMPS data in this file are truncated at approximately 0.67 um. One of the fifteen 1.9 cm diameter tubes was used to supply ambient air to the APS (TSI 3320) located in the humidity controlled box at the base of the mast. Number size distributions were collected every 15-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 15-minute data were averaged into 30-minute periods centered on the hour and half-hour. The value of -999 is assigned to any 30-minute period without data. The APS data have been converted from aerodynamic diameters to geometric diameters using calculated densities. 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 (Quinn and Coffman, 1998). These calculations assume the aerosol is internally mixed. The end product is a density distribution for each impactor sampling period. The APS data reported here are in 24 size bins with original aerodynamic diameters ranging from 0.9 to 4.7 micrometers. Data at diameters larger than 5 um were discarded due to potential interferences from phantom counts and uncertainties in large particle collection efficiencies. Depending on the density, there are some periods where the APS data (reported in geometric diameter) overlap with the DMPS data. The data have been separated into separate files that correspond to the impactor sampling periods. This was done in order to use the calculated densities from each of these periods. Data are reported in geometric diameter (micrometers) in units of dN/dlogDp (cm-3) at a "wet" measurement RH of 55%. The APS data are also available in the data archive with the original aerodynamic diameters. Format: comma-delimited ASCII. DOY (Julian Decimal Date) (UTC) Latitude (positive North, negative South) Longitude (positive East, negative West) File Name Conventions: NSD_wet_YYYMMDDHH.csv where NSD indicates number size distribution, wet indicates the measurement RH of 55+/-5% and the YYYMMDDHH is the start time for the impactor sampling period. References: Quinn, P.K., and D.J. Coffman, Local closure during ACE 1: Aerosol mass concentration and scattering and backscattering coefficients. J. Geophys. Res., 103, 16,575- 16,596, 1998.