Tim Bates, bates@pmel.noaa.gov, May 7, 1998
206-526-6248, fax 206-526-6744
R/V Discoverer ACE-1
NOAA-PMEL
Short Description: Shipboard particle number size 
distributions (30 minute averages), APS data at measurement 
RH (40%)
Two data files, Leg 1 (Seattle to Hobart) and Leg 2 
(intensive)
Keywords: APS, Measurement RH

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  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  aerodynamic diameter (micrometers) in  units of 
dN/dlogDp  (cm3) at  the  measurement RH  of  40%. The  data 
reported  here  are  in  26  size bins  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  same APS  data are  also  available in  the ACE-1  data 
archive adjusted to geometric diameters and dry RH.