NOAA ship Discoverer
Ancillary Data
Reduced and Compiled by NOAA-PMEL
Version 1, 26 July 1996
Celine Mari,Jim Johnson and Tim Bates

Data File NO.dat contains the following parameters:

DOY
NO

DOY
The data are compiled in one hour averages. The time is given as decimal 
day of year (DOY) such that DOY 32.5 is 12 noon GMT on February 1.


NO (see discussion above)

NO was collected on the R/V Discoverer.  This section of the report 
summarizes the experimental method, the results obtained during ACE-1 
and an initial analysis of the data. 

1. Instrument and Operation

The instrument used during the cruise is based on the chemiluminescence 
of the NO + O3 reaction. This high-sensitivity technique allows a 
measure of sub-ppbv (part per billions by volume) concentrations. The 
instrument is described in details by Honrath and Jaffe ( J.Geophys.Res 
1992,97,20,615-20,630).  Briefly, NO is determined by mixing a 1 
standard liter per minute flow of ambient air with a small flow of 4% O3 
in O2 in a gold plated reaction chamber. Chemiluminescence resulting 
from the NO + O3 reaction is monitored by an adjacent photomultiplier 
tube and a computer using photon counting techniques. This instrument 
can also measure NO2 using an NOy converter but this option was not 
operational during the cruise.


2. Data Reduction
The initial data were carefully screened to eliminate values potentially 
affected by the ship exhaust. In our case, due to the instrument 
location on the ship, all the measurements for which corresponding 
relative wind direction were out of the range -55 to +55 degree were 
discarded. The NO artifact (the observed NO concentration when the 
actual concentration is zero) was determined using nighttime 
measurements (defined when solar radiation measured on the ship was less 
then 5 Watt/m2), during periods unaffected by nearby sources. The NO 
artifact during the cruise mostly ranged between -10 to +10 pptv with a 
few occurences of much higher values (up to 50 pptv). In these few 
cases, the unreasonable nighttime values prevent any interpretation of 
the values measured during the day.  The random variability due to 
photon counting noise is an other source of uncertainty in the NO 
measurement.  This variability determines the NO detection limit.  


3. Results and Discussion
The data reveal a background hourly averaged values from a few to 50 
pptv.  During periods when the ship was in continental air masses (as 
determined by soot and radon measurements) NO values grows up to 100 or 
200 pptv.  There was only one period (Julian Day 309) when values were 
unexplanably high.  The photolytic reaction shown above is assumed to 
dictate the NO behavior.  Thus, NO is expected to have a strong diurnal 
cycle.  Some diurnal cycles were observed during the cruise.  Although 
the data are still preliminary (further analysis of the instrument 
uncertainties and correlation with other availables data such as back 
trajectories are necessary to improve the data analysis), they provide a 
useful data set for modeling activities by giving a reasonable 
indication of the NO mean value during periods of interest.