Ship's speed and heading
The heading (compass degrees) was taken from the ship's gyro which was recorded by the Discoverer's SCS system. For the times when the SCS system was not working, the heading was taken from the PMEL GPS course. The GPS course and the gyro heading usually agreed within several degrees as long as the ship was moving forward through the water at speeds above 5 knots. The ship's speed (knots) was taken from the PMEL GPS system. Both the speed and heading were averaged from the one minute data to make the 30 minute averages. The speed was averaged directly, the heading was separated into N and E components by taking the sin and cos respectively of the heading. After averaging the N and E components into 30 minute bins, the heading was recalculated using a 4 quadrant arctangent function.
Atmospheric Temperature and Humidity:
Air temperature and humidity were measured with the ship's RM Young sensor. The sensor was enclosed in an RM Young radiation shield. The data were averaged into 30 minute bins.
Barometric pressure was measured with the PMEL Qualimetrics sensor. The data were corrected using a linear regression with the ship’s barometer and averaged into 30 minute values.
Total solar radiation was measured with an Epply Black and White Pyranometer (horizontal surface receiver -180, model 8-48, serial number 12946) and an Epply precision pyranometer (horizontal surface receiver - 180 (twin hemispheres), model PSP, serial number 133035F3) that were mounted on the top of AeroVan. Both instruments were calibrated by The Epply Laboratory on October 11, 1994. There were times when the sampling mast shaded the sensor. Most of these times occurred for about a 30 minute period in the afternoon. (When the ship was traveling South, the mast was West of the sensor). There were also times when the ship's mast shaded the sensor. These "bad" data due to shading have not been edited out of the 30 minute data record. The data reported here are 30 minute averages of the Epply 8-48 (SN 12946) in watts per square meter. Any 30 minute period without valid data is marked with a -99.
Wind speed and direction were measured with the PMEL Qualimetrics anemometer and the Ship's RM Young anemometer. The PMEL anemometer was mounted above the top of the rain/seaspray shelter at the top of aerosol/gas sampling mast. The location of the PMEL anemometer was chosen primarily to select the times when the sampling mast was in the 'clean' sector, not being influenced by ship pollution. The ship's RM Young anemometer was located on the starboard side of the ship's mast, 33 meters above the water. The PMEL anemometer and ship anemometer were calibrated in the PMEL wind tunnel in July and October 1995, respectively.
The data from the PMEL anemometer were recorded on the PMEL data logger as one minute averages. The data from the ship's RM Young anemometer were recorded on the ship's SCS data system as one minute averages.
The final 30 min average data are reported in 6 columns:
RelWindS, RelWindD, WindS, WindD, WindU, and WindV
Relative wind speed (RelWindS) is the 30 minute average of the wind speed (in m/s) relative to the ship. The relative wind direction (Rel WD) is the 30 minute average of the wind direction relative to the bow of the ship (0 degrees, wind is dead ahead; +90, wind is from the starboard beam; -90, wind is from the port beam). Because the relative wind information is used primarily to determine local ship pollution episodes for air sampling, the PMEL anemometer was used exclusively for the reported relative wind.
True wind speed (WindS) is the 30 minute average of the true wind speed in m/s. True wind direction (True WD) is the 30 minute average wind direction in compass degrees. The PMEL anemometer was located closer to the superstructure of the ship and the wind that it measured was more distorted than that measured by the ship's RM Young anemometer. Thus, the RM Young anemometer was used to derive the true wind speed and direction. During the few times when the SCS system was not working, the PMEL wind data were used.
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
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 North and true East components of the wind. These components and the resulting (computed) speed and direction at one minute intervals were plotted. A few outliners were eliminated and the resulting data were reduced into 30 minute averages. The averaged North and East components were then used to calculate the 30 minute average wind speed and direction.
Two ozone uv analyzers were used, a Dasibi 1008 AH ,and a TECO 49. Both analyzers were calibrated to a NIST traceable analyzer at the NOAA-CMDL lab prior to the project. One minute averages of the output of each 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 was cleaned, the calibration function from CMDL (offset and slope) was applied, and 30-minute averages were created. The 30-minute average from each instrument was then averaged together to create the final data.
Radon was measured with a dual-flow-loop two-filter radon detector constructed at PMEL by Stewart Whittlestone (ANSTO). The system was calibrated with a dry radon source (Pylon Electronics Corp. Canada - 2737 mBq/min) and intercalibrated in Hobart at the beginning of the experiment (Nov.) with the source used by Stewart Whittlestone. The radon data set includes all data points with the exception of the instrument calibration periods in Seattle and Hobart. The data are reported in units of mBq per cubic meter. A background value of 20 counts was used in the data reduction. This value was based on the lowest 2.5 hr running mean values obtained during the transit cruise. These low values occurred at approximately 10 degrees south. Occasionally the 30 minute data were less than the background value of 20. In these cases a radon concentration of zero was entered in the 30 minute data. The radon data were smoothed with a 2.5 hour running mean.
Total Particle Number (UFCN)
The total number of particles with diameters 3nm were measured with a TSI 3025 UFCN at the base of the aerosol sampling mast. Missing and polluted data values have been replaced by -99. Units are particles per cubic centimeter averaged over the 30 min
The rainfall rate was measured with a Scientific Technology Inc. ORG-100 Optical Precipitation Intensity Sensor. The instrument was mounted on the railing of Aero van and was used along with wind direction, wind speed and CN to control the aerosol chemistry pumps. The dynamic range of the sensor is 0.5 to 1600 mm/h. Spikes in the signal are often associated with sea spray. The 30 minute averaged data include all data points. The data are reported in units of mm/hr. (Note: since the data are 30 minute averages, summing all 48 points for one day and dividing by two will give total precipitation in mm for that day.)
Aerosol light scattering
ScatBlue, ScatGreen, ScatRed are the 60-minute averages of the total aerosol light scattering as measured by the PMEL TSI 3-wavelength (450,550,700nm) nephelometer. The instrument was calibrated on the cruise using CO2. Two impactors were placed upstream of the nephelometer. One had a nominal size cut of 10 um and the other of 1 um (at 55% RH). A valve was switched every 15 minutes by the data logger so that either light scattering of the total aerosol or of the submicron aerosol light scattering was measured.
Submicron aerosol light scattering data are in the columns SubSctB, SubSctG, SubSctR. All light scattering is given in units of Mm-1, inverse megameters (1 Mm-1 = 1E-6 m-1). Missing and polluted data values have been replaced by -99.
Aerosol light absorption
The aerosol light absorption data are compiled as the 60-minute averages of the aerosol absorption coefficient at 550nm as measured by the PMEL PSAP (Radiance Research Inc.). Light absorption is given in units of Mm-1, inverse megameters (1 Mm-1 = 1E-6 m-1). Missing and polluted data values have been replaced by -99.
Seawater temperature and salinity
Seawater temperature and salinity were measured with the ship's thermosalinograph (Seabird SBE-21 serial number 843) and recorded on the ship's SCS system. The instrument was calibrated by the NW regional Calibration Center on 10/11/95 just before the cruise. The instantaneous one-minute data set from the ship was very clean and required very little editing. The data were averaged into 30 minute bins. Temperatures are reported in degrees C. Salinity data are in practical salinity units (psu).
Water from the ship's underway pumping system (5 meter depth, bow intake) was run through the underway auto analyzer system to measure surface nitrate + nitrite concentrations. The instrument samples at 10 minute intervals: seawater, blank, seawater, blank, standard, blank; repeating this sequence each hour. The instrument was started on DOY 295 (after Hawaii) and worked well throughout the remainder of the project. Data are marked with either a concentration, 0 (indicating below detection limit), or -99 (when there were no data). The lower limit of detection was generally 0.05 micromolar but was as low as 0.02 micromolar at times. All data reported here are in units of micromoles per liter.
Air and seawater were immediately analyzed aboard ship for DMS concentrations using the same automated collection/purge and trap system. Air samples were collected through a Teflon line which ran approximately 60 m from the top of the aerosol sampling mast (17 m above sea level, forward of the ship's bridge) to the analytical system. One hundred ml/min of the 4 L/min flow were pulled through a KI solution at the analytical system to eliminate oxidant interferences. The air sample volume ranged from 0.5 to 1.5 L depending on the DMS concentration. Seawater samples were collected from the ship's seawater pumping system at a depth of approximately 5 m. The seawater line ran to the analytical system where 5.1 ml of sample were valved into a Teflon gas stripper. The samples were purged with hydrogen at 80 ml/min for 5 min. Water vapor in either the air or purged seawater sample stream was removed by passing the flow through a -25C Teflon tube filled with silanized glass wool. DMS was then trapped in a -25C Teflon tube filled with Tenax. During the sample trapping period, 6.2 pmole of methylethyl sulfide were valved into the hydrogen stream as in internal standard. At the end of the sampling/purge period the coolant was pushed away from the trap and the trap was electrically heated. DMS was desorbed onto a DB-1 mega-bore fused silica column where the sulfur compounds were separated isothermally at 50C and quantified with a sulfur chemiluminesence detector. The detection limit during ACE-1 was approximately 0.8 pmole. The system was calibrated using gravimetrically calibrated permeation tubes. The precision of the analysis, based on both replicate analyses of a single water sample and replicate analyses of a standard introduced at the inlet of the air sample line, was typically +- 8%. The performance of the system was monitored regularly by running blanks and standards through the entire system. Values reported here have been corrected for recovery losses. System blanks were below detection limit. Seawater concentrations are reported in units of nanoMolar, nM, air concentrations are reported in units of parts per trillion, ppt .
Discrete chlorophyll samples were collected approximately every four hours while underway from the ship's seawater sampling line. The inlet was located approximately 5 m below the surface at the bow of the ship. Chlorophyll samples were also collected at each sampling depth at each station. Samples were collected (530 ml), immediately filtered, put into 10 ml of 90% acetone, and frozen by ship's survey department. The samples were analyzed within 3-4 days aboard ship with using a Turner fluorometer. The fluorometer was calibrated after the cruise using chlorophyll 'a' from the Sigma Chemical Corp. The data are reported in units of micrograms per liter.
Discoverer Impactor (2-stage) Data
Submicron and supermicron aerosol ionic concentrations.
Data Set Description:
ACE-1, PMEL 2-stage impactor data collected onboard the Discoverer. Please contact Trish Quinn when using data (Patricia.K.Quinn@noaa.gov)
Ion concentrations are given in ug/m3. Submicron values represent the ion concentration in all particles with aerodynamic diameters < 1.0 um. Supermicron values are for particles with aerodynamic diameters > 1um and < 10 um. Diameters are given for the relative humidity of the sampled air stream.
Uncertainties associated with the ion concentrations range from +/- 5 to 25%.
U.S.Dept of Commerce / NOAA / OAR / PMEL / Atmospheric Chemistry