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Atmospheric Temperature and Humidity:
Atmospheric temperature and dew point were measured with the PMEL Qualimetrics instrument using an RTD for temperature and a LiCl cell for dew point. The sensor was enclosed in an aspirated housing mounted on the railing of Aero van approximately 14 m above sea level.
Barometric Pressure
Barometric pressure record was taken from the ship's bridge deck weather log of hourly measurements. The ship's barometer was calibrated by the National Weather Service.
Insolation (sunlight)
Sunlight was measured with a model 8-48 Eppley Radiometer (SN 12946) that was mounted on top of the Aero Van (14m asl). There were times when the sampling mast shaded the sensor. These shaded data were not been edited out of the 30 min data record.
Wind
Winds were measured with the PMEL Weather Measure Skyvane (located on the sampling mast on AeroVan approximately 18 m asl). The wind data were stored as one minute averages. The ship's gyro compass input was used to correct the relative wind to true wind. The wind vector was separated into North and East components and the ship’s velocity vector components (as determined from the GPS record) were subtracted to find the true N and true E components of the wind.
WindD is the true wind direction in compass degrees.
WindS is the true wind speed in m/s.
WindU is the true wind east-west component, wind from the east to the
west is positive.
WindV is the true wind north-south component, wind from the south to
the north is positive.
RelwindS is a 30 min average of the wind speed (in m/s) relative to
the bow of the ship.
RelWindD is a 30 min average of the wind direction relative to the
bow of the ship where:
0 wind is dead ahead
+90, wind is coming from the starboard beam
-90, wind is coming from the port beam
Ship’s position, course and speed
The ship’s position was obtained from Tony Amos’ (U. Texas) GPS and recorded on his data system. Latitude and longitude are given here at even 30 minute intervals with no averaging. For those times when there were no data at the 30 minute point, a value was interpolated from the existing data. The course (compass degrees) and speed (knots) were computed from the differences in position.
Aerosol scattering and total number
Light scattering by aerosol particles (ScatBlue, ScatGreen, ScatRed) was measured with the UW Civil Engineering Department nephelometer (Bodhaine et al., Atmos. Environ., 25A, p2267-2276, 1991). The instrument was calibrated on the cruise using CO2. The scattering values are in units of x10^-6 m^-1 (inverse Megameters, Mm^-1). CN > 12 nm and CN > 3 nm (UFCN) were measured with PMEL TSI CN counters.
Ozone
Ozone was measured with a Dasibi 1008 AH ozone analyzer. The analyzer was calibrated to a NIST traceable analyzer at the NOAA-CMDL. One minute averages of the output of the analyzer were recorded on the PMEL data system and plots were made of the raw data. A small portion of the data was deleted (consisting mostly of times that the inlet air was passed through a zero filter - usually when the relative wind was well behind the beam of the ship). After the raw data were cleaned, the calibration function from CMDL (offset and slope) was applied, and 30-minute averages were created.
Sea surface temperature and salinity
Sea surface temperature and salinity were measured with a SBE-21 #332 thermosalinograph calibrated on 9/5/91. Based on the calibration the measured temperatures were accurate to within 0.004 degrees. The data were recorded on Tony Amos' (U. Texas) data logger system. There were several days of missing data.
Nitrate
The underway autoanalzyer system was used to measure surface nitrate and ammonium concentrations and pH. Data are marked with either a concentration in micromoles per liter, 0 (indicating below detection limit), or -99 when there were no data. A reported value of 30 uM means indicates that the signal was offscale and that the true value was greater than the upper limit of 25 to 30 uM..
Chlorophyll
Discrete chlorophyll samples were collected twice per day initially and then four times per day on the last 2 weeks of the cruise. The values agreed well with the data of Walter Hebling (SIO). PMEL and SIO had continuous flow fluorometers each operating for part of the cruise. The SIO continuous record (JD80-100) was combined with the PMEL record (JD100-127) for the final data set. The continuous record was calibrated with the discrete samples using a linear regression forced through zero (PMEL - chlorophyll = continuous reading * 0.0185, for SIO - chlorophyll = continuous reading * 0.0181). There was evidence of a diurnal cycle in both the PMEL and SIO continuous records in regions of high chlorophyll. Keeping the sample line dark had no effect on the diurnal cycle. No attempt was made to eliminate the diurnal cycle in the final data reduction since there was no significant difference in the regression analysis using day vs. night samples. Although the solar radiation measurement could have been incorporated in the data reduction to lessen the diurnal cycle in regions of high chlorophyll, the corrections would have induced a diurnal cycle in regions of low chlorophyll.
Methane and Carbon Monoxide
Sampling
Gas partial pressures were measured continuously in surface seawater along the cruise tracks using an equilibrator system designed to partition dissolved gases into a vapor phase for sampling. The equilibrator was fed with seawater pumped directly to the laboratory area from an intake located at approximately 5 m depth near the bow of the ship. The equilibrator was constructed from Plexiglass and consisted of a 20 enclosed headspace continuously showered with 15-20 L/min of seawater. Approximately every hour, 2 ml of gas were withdrawn from the headspace for analysis.
Air samples were pulled from the bow of the ship, 10 m above the sea surface, to the oceanographic laboratory (approximately 40 m) through plastic coated aluminum tubing (Dekoron) at a flow rate of 10 L/min. Dekoron tubing was also used to connect the equilibrator to the analytical system.
Analysis
Gas partial pressures were measured with an automated, temperature controlled, gas chromatographic system containing both a flame ionization detector (FID) and a mercury bed detector (MBD). Air samples from the air sampling line, the equilibrator, or a standard stream were dried using phosphorous pentoxide or potassium permanganate and drawn into a 2 ml sample loop connected to an automated sample valve. The gases were separated using a series of five columns with CO valved to the MBD and CH4 valved to the FID. The system was automated with a Carle Series 400 Controller and ran unattended with alternating injections of air, standard, and equilibrated air with the series repeated approximately each hour.
Data Reduction
The raw signals were first visually filtered to eliminate any episodes of ship contamination or instrument malfunction. CO and CH4 mixing ratios in both air and equilibrator samples were then computed based on peak height (CH4) or peak area (CO) and a six-hour running-mean single or dual-point standard. The CH4 data were further smoothed using a 12 hour weighted regression. The dry-air mixing ratios were then binned into hourly values based on the measurements made 30 minutes before and after the hour. The partial pressures measured in the equilibrator samples were corrected for warming during transit from the water intake to the equilibrator using a ratio of the seawater solubilities at sea surface temperature and the equilibrator temperature. The warming values were derived from the regression of hourly warming on sea surface temperature. The seawater phase concentrations were calculated from the measured equilibrator partial pressures and the solubility relations found in Wiesenburg and Guinasso (J. Chem. Eng. Data, 24 p356-360, 1979)
Standards were dried, whole-air mixtures contained in aluminum cylinders and were calibrated by NOAA/CMDL. CO and CH4 mixing ratios are referenced to the CMDL and Rasmussen scales, respectively. The accuracy of the standards, as determined by CMDL is ± 2% and ± 1.5% for CO and CH4, respectively. During these cruises the instrument precision, as determined by the average percent standard deviation of the standard response over a six hour period, was approximately ± 1.5% and ± 1.8% for CO and CH4, respectively.
DMS
DMS was measured with a Gas Chromatograph System. Details can be found in Bates et al., J. Geophys. Res. 103, 16369-16,383, 1998 and Bates and Quinn, Geophys. Res. Lett., 24, 861-864, 1997.
U.S.Dept of Commerce / NOAA / OAR / PMEL / Atmospheric Chemistry