SOS99NASH_WP3D_1sCHM.txt read me file

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Principal Investigators and Contact Information:

CO: Holloway, John
NOAA Aeronomy Laboratory
Mail: R/AL7 325 Broadway, Boulder, CO 80307
Email: jholloway@al.noaa.gov
Phone: 303-497-3273

O3: Parrish, David
NOAA Aeronomy Laboratory
Mail: R/AL7 325 Broadway, Boulder, CO 80307
Email: dparrish@al.noaa.gov
Phone: 303-497-5274

NO: Ryerson, Tom
NOAA Aeronomy Laboratory	
Mail: R/AL7 325 Broadway, Boulder, CO 80307
Email: tryerson@al.noaa.gov
Phone: 303-497-7531

NO2: Ryerson, Tom
NOAA Aeronomy Laboratory	
Mail: R/AL7 325 Broadway, Boulder, CO 80307
Email: tryerson@al.noaa.gov
Phone: 303-497-7531

NOy: Ryerson, Tom
NOAA Aeronomy Laboratory
Mail: R/AL7 325 Broadway, Boulder, CO 80307
Email: tryerson@al.noaa.gov
Phone: 303-497-7531

HNO3: Huey, Greg
Georgia Institute of Technology
Georgia Institute of Technology, School of Earth & Atmospheric Sciences, Atlanta, GA 30332-0340
Email: greg.huey@eas.gatech.edu
Phone: 404-894-5541

SO2: Holloway, John
NOAA Aeronomy Laboratory	
Mail: R/AL7 325 Broadway, Boulder, CO 80307
Email: jholloway@al.noaa.gov
Phone: 303-497-3273"

CO2: Dissley, Rich
Ball Aerospace	
Mail: Ball Aerospace & Technologies Corp., Mail Stop T-3, 1600 Commerce St., Boulder, CO 80301
Email: rdissley@ball.com
Phone: 303-939-5763

The notes below are given by the Investigators for their instruments.

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CO:
These data are the 1 second determinations of carbon monoxide mixing ratios (ppbv).  The measurements are based upon CO vacuum ultraviolet fluorescence.

The 1sigma detection limit of the data is 1-2 ppbv.  We estimate the random uncertainty of the measurement to be 2.5%.  The concentration of our calibration standard is known to within about 4%.

There is no data for 11 July.


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O3:
These data were finalized November 18,1999.  Each file is chemiluminescence ozone data.  The Chemiluminescence data were normalized to the TECO data in preflight zero air to provide calibration and compared with the TECO data in ambient air.   

Units are ppbv.

The data are 1 second averages and the instrument response was better than 1 second.  

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NO, NO2, and NOy:

NO - nitric oxide, units of ppbv; detected using ozone-induced chemiluminescence (CL).  Total measurement uncertainty for the 1-second averaged data is given as (1-sigma precision + 1-sigma accuracy) and for [NO] ~ 0 is estimated as (40 pptv + 5%).  Because of uncertainties in instrument background count rates, this cannot be improved beyond 15 pptv at low [NO] by averaging over longer periods of time.


NO2 - nitrogen dioxide, units of ppbv; detected using UV photolysis followed by CL.  These data are still preliminary, and instability in the NO zero level (see above) also affected the retrieval of NO2 in this data set. Total measurement uncertainty for the 1-second averaged data is given as (1-sigma precision + 1-sigma accuracy) and for [NO] ~ 0 is estimated as (200 pptv + 10%).
There is no NO2 data for flights 6/26/99 and 7/7/99.


NOy - total gas-phase reactive nitrogen oxides, units of ppbv; detected via Au-tube conversion to NO with added CO followed by CL.  In-flight HNO3 conversion efficiency was 96  2% (n = 24) over the SOS '99 mission, derived from standard addition of ca. 7 ppbv HNO3 into ambient air within 1 cm of the inlet tip.  Instrument time response to HNO3 is described by a two-exponential fit with time constants of 0.7 s (98% of total) and 14 s (7% of total).  In-flight NO2 conversion efficiency was 97  3%.  Total measurement uncertainty for the 1-s averaged NOy data is estimated as (110 pptv + 10%).

Sensitivities have been interpolated between calibrations as a function of measured ozone (NO and NO2 channels only) and water vapor.  Background counts have been interpolated between measurements as a function of ambient water vapor.  Both NO and NO2 measurements take into account NO oxidation during sampling (e.g., Ridley et al., JGR, 93, 15,813-15,830, 1988); for SOS '99, for NO, this correction averages 2-4% and was at most 6%.

Detailed descriptions of the instrument can be found in the following papers:
JGR, 104, 5483-5492, 1999.
JGR, 105, 26,447-26,461, 2000.
Operational details are available on request.  


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HNO3:
Nitric acid is available for all flights except for the 6/26 transit flight from Tampa to Nashvile, the 7/3 flight - lost a detector, and the 7-17 flight - converted to positive ions.

Units are pptv.
The 2 sigma accuracy is +/- 25%
The precision is ~ 100 pptv for a 1 second sample (1 sigma)

Accuracy and precision was reduced for the 7/4 flight where the system was plagued by electrical noise. During this flight the accuray is 25% + 1 ppbv. The noise is so bad that only the high concentration data should be taken into consideration i.e. do not try to interpret the nitric data in the regional background on this day.

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SO2:

These data are the 1 second averages of sulfur dioxide mixing ratios (ppbv).  The measurements were made using a TECO 43C-TL pulsed fluorescence instrument that has been modified for aircraft operation.

The random uncertainty of the data is 10% to 12%  0.2 ppbv.    The field standard used is from Scott-Marrin.  The stated uncertainty of the analysis provided with the standard is  2.0 %.  The analysis is traceable to NIST SRM 1693a.


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CO2:

The instrument precision is ~150 ppbv (1 sigma in 1 sec), calculated during instrument zeros (constant CO2 mixing ratio in both sample and reference cells).  The precision is roughly constant for all flight conditions, and is similar to that measured in the lab.

The measurement accuracy is determined by propagating all measurement uncertainties: calibration and reference tank concentrations, calibration and reference mass flow rates, instrument zero and precision.  Accuracy under lab conditions is 0.13%, or about 450 ppbv for a CO2 concentration of 360 ppmv.  The accuracy during flight is ~3x worse, due primarily to vibrational noise in the mass flow controllers.
   
The sample mass flow rate does not maintain its set point above 5000 m, which changes the instrument zero level.  However, the instrument was zeroed at enough different altitudes to determine the dependence on sample flow rate.  The final data incorporate this correction, but the preliminary data did not.  The dependence is the same for all flights.
	
Water vapor affects the CO2 signal primarily by dilution, i.e., an increase in H2O partial pressure causes a decrease in the partial pressure of all other constituents.  The LICOR made measurements of water vapor absorbance simultaneously with CO2, and this signal has been calibrated to water vapor number density.  The CO2 concentration has been corrected in the final data to account for the amount of water vapor in the sample.  This correction is always small, on the order of 200-300 ppbv in CO2.

The uncertainty in the instrument zero was usually less than the trend in the zero level for a given flight.  Zero trends were either linear or exponential; the zero applied to the data was the best fit to the trend for each flight.  

The uncertainty in the instrument sensitivity (i.e., absolute calibration) was greater than any apparent trend for all flights.  Therefore, an average sensitivity was calculated for each flight and applied to the data for that particular day.


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