Readme File for Huebert Group C-130 Total Aerosol Sampler 16 April 2002 Title: Aircraft C-130 Bulk Aerosol Mass of Anions and Cations from TAS (Huebert) Authors: PI: Barry J. Huebert Co-PIs: Byron Blomquist Jackie Heath Steve Howell Tim Bertram Technician who ran samples and processed data: Liangzhong Zhuang Dept. of Oceanography 1000 Pope Rd., MSB 407 (only needed for courier deliveries) University of Hawaii Honolulu, HI 96822 USA 1-808-956-6896 phone 1-808-956-9225 fax 1.0 Data Set Overview This data was collected from the NCAR/NSF C-130 during the ACE-Asia program. It consists of samples collected using a Total Aerosol Sampler (TAS) and analyzed using ion chromatography on site. We report soluble chloride, nitrate, sulfate, oxalate, sodium, ammonium, potassium, magnesium, calcium, and nonseasalt sulfate. Each of these is accompanied by an uncertainty derived by propagating errors from the blanks, flowmeter, and analytical procedures. Included in the data set are the start and stop times of each sample, as well as the location and altitude of the C-130 at the start and end of each sampling interval. These locations and altitudes are GPS values from the NCAR-RAF data system. More detail on the location of each leg and the conditions of each flight can be found in the C-130 Flight Reports and C-130 data in the ACE-Asia catalog (http://www.joss.ucar.edu/ace-asia/dm/). The first reported samples are from the second research flight (RF02), flown on 2 April 2001 Japan time. (The takeoff time was just before midnight on 30 March UTC. All times and dates in the data file are UTC.) All research flights have a sample name starting with RF and were flown from Iwakuni MCAS, Japan. The last sample is from the last research flight, RF19. 2.0 Total Aerosol Sampler Description The TAS sampler was located outside the fuselage on the right side of the C-130. It is designed so that every particle entering its tip can be extracted and analyzed. A separate filter/cone unit is inserted into the sampler (by reaching through an access door from inside the aircraft) for each sample collected. All particles entering TAS will be either collected on the filter or deposited to the inner walls of the cone. By separately extracting both the interior of the cone and the filter and dividing the mass of each analyte by the volume of air sampled, we derive a defendable ambient bulk concentration of each analyte. Since there is no inlet tube (except for the liner that we extract after exposure), there is no concern about inlet losses causing sampling artifacts. A sealing mechanism closes the sampler except during exposure, to prevent contamination during changes of filter/cone unit. The removable cones that line the diffuser are about 150 mm in length, with an inlet orifice of about 6 mm diameter and an exit of just over 74 mm diameter. The exit opening is configured to sit tightly against a 90 mm Teflon filter. The cones are coated with Teflon to minimize the collection of acidic gases like nitric acid. The external tip of the structure that holds the removable cones was sized to allow for isokinetic sampling at a range of C-130 airspeeds (roughly 100 - 140 m/s). The nominal flowrate was 100 lpm, but this was manually adjusted in flight to achieve isokinetic sampling on each leg. Flows were measured by a Kurz thermal mass flowmeter, which was calibrated against a volumetric standard before and after the field program. Most samples were exposed for between 20 and 60 minutes. TAS cones were extracted by agitating for 2 minutes with 30 ml of DI water. All Teflon filters were pre-washed in ethanol and DI water prior to the program to reduce nitrate and sodium blanks that have been erratic in Gelman Zefluor filters recently. After exposure each filter was placed in a microclean polyethylene bag and extracted using 1 ml of ethanol (to wet the filter) and 9 ml of weak acid solution (10-5 M trifluoroacetic acid) in an ultrasonic bath. The weak acid prevented the loss of ammonium ion, but it probably increased the dissolution of carbonates (and Ca?) relative to distilled water. All cone and filter extracts were analyzed by ion chromatography as soon after a flight as possible. In some cases the analysis began the evening after the flight, but in a few cases analyses were delayed by 2-3 days due to IC problems. The extracts of cones and filters were analyzed by suppressed ion chromatography on two Dionex ICs (one for anions and one for cations), using procedures identical to those described by Huebert et al. (JGR, 103, 16493-16510, 1998). 3.0 Data Collection and Processing 3.1 Description of data collection Teflon filters and cleaned cones were assembled in a glove box the night before each flight. On each C-130 flight, all 7 sets of pre-loaded filter/cone units would be brought aboard. Usually one or more would be loaded with Nuclepore to collect inlet-less samples for SEM analyses by Jim Anderson. When ready for sampling, the operator (either Tim Bertram or Jackie Heath) would load a filter/cone unit into TAS, lock it in place, and close the access door. When a sampling leg began, the inlet closure valve and a rear valve (to the flowmeter and pump) would quickly be opened to start flow through the sampler. Over a period of about a minute, the operator would adjust valves to achieve isokinetic flow. Flow would continue to the end of that sampling leg, at which time the valves were closed as nearly simultaneously as possible. This filter/cone unit would then be replaced by one for the next sample. The units were always changed with gloved hands and stored in sealed containers. 3.2 Description of derived parameters and processing techniques used Mass flow for each sample was recorded from the Kurz mass flow meter on both the RAF data system and our own personal computer. From these recorded values, sample volume was calculated. Each flowmeter was calibrated prior to and after the program. Uncertainties in the flows were estimated at 5%. 3.3 Description of quality control procedures During each flight one field blank was exposed. This was a filter/cone unit just like the others, which was mounted in the TAS and exposed for just 10 seconds. Thus, its handling and history were identical to the actual samples. The analyte for that flight's blank filter was subtracted from each of the filters (or cones for the cone blank) on that flight. Uncertainties were derived by propagating the errors from the flowmeters (5%), instrument detection limit, the entire project blank variability (so they are generous for any one flight), and the analytical uncertainty. 3.4 Data intercomparisons To test our analytical procedure, we participated in an ACE-Asia inter- laboratory comparison organized by Trish Quinn of NOAA-PMEL. She distributed solutions for checking the calibration of ICs. We took our intercomparison samples to Japan and ran them under the conditions of the field analyses. While we do not have the results handy at the time of this writing, our group compared nicely with the others and the known concentrations. In short, IC calibration errors are not likely to be the cause of any problems with the data reported here. Anyone wanting more details can contact the authors or Trish Quinn to see the details of this QA intercomparison. 4.0 Data Format The file structure is a tab-delimited ASCII file, with a carriage-return to mark the end of each line. The data is in 41 columns with 70 rows. The first row is a listing of the tabulated parameters. The second row is a listing of units. All subsequent rows contain the data from a single airborne sample. No missing data indicators were needed. Note that we chose NOT to use "less than" symbols for values that were below the detection limit. Rather, each apparent analytical value is tabulated alongside its uncertainty. The only exception is a few slightly negative values (due to blank subtraction from lightly loaded filters) which were set to zero. In some samples there was not enough analyte to exceed the blank variability and other sources of uncertainty, so the uncertainty is larger than the value. Tabulating the data this way puts the responsibility on the data user to avoid interpreting values that are below the detection limit. We elected to use this approach for two reasons: when computing average values it is always a challenge to know how to treat "less than" values. By leaving the apparent value in, that gives a slightly more informed value to use for averages than half the detection limit. Furthermore, since we used the variability of blanks throughout the whole program as the basis of our uncertainty calculations, we believe the actual detection limit is better than what we cite. Most blank levels were several times higher after the first several flights (when we had just set up our portable IC lab and glove-boxes), dropping to a more stable level after our lab had been running for about a week. That will cause an overestimate of the blank variability for any one flight. The columns are: 1. Start Date and Time of the sample, as YYYYMMDDHHMMSS. For the first 19 samples no seconds were recorded, so the number ends with two x's. All times and dates are UTC. 2. End Date and Time of the sample, as YYYYMMDDHHMMSS. For the first 19 samples no seconds were recorded, so the number ends with two x's. Note that one sample was turned off temporarily (for rain showers), so there is an intermediate off and on which is listed under "Comments." 3. The UH sample number: Flight Number (RF02) and approximate start time as HHMM. In the files at UH this would also be followed by a "T" (for TAS), which has been removed here. 4. Start_Alt: The pressure altitude at the beginning of this sample, in meters above sea level (ASL). In some cases (especially on radiation flights, where the legs were generally shorter), a single sample may have integrated over several altitudes. In other cases the start altitude is probably the better measure of the sample altitude, because the time-lag to start all the samplers at the beginning of a leg means that the plane had probably stabilized its altitude by the time the sample flow began. That same time-lag at the end of the leg, however, increases the likelihood that the listed stop time may be after the plane had begun changing altitudes. Note that these altitudes and locations are provided as a guide only, and serious use of position data should be accompanied by looking at the detailed flight data in the C-130 files, which we cannot reproduce here. 5. Stop_Alt: the C-130 pressure altitude at the time the sample was terminated, in meters ASL. 6. Start_Lat: the gps-derived latitude, in decimal degrees (positive north) at the start of the sample. 7. Stop_Lat: the gps-derived latitude, in decimal degrees (positive north) at the end of the sample. 8. Start_Lon: the gps-derived longitude, in decimal degrees (positive east) at the start of the sample. 9. Stop_Lon: the gps-derived longitude, in decimal degrees (positive east) at the end of the sample. 10. Cl: Chloride ion concentration. The units are micrograms of chloride per standard cubic meter of air. Standard conditions are 1 atmosphere (1013 mbar) and 298 degrees K. 11.Cl-Unc: the propagated uncertainty in chloride concentration 12. NO3: Nitrate ion concentration. The units are micrograms of nitrate per standard cubic meter of air. Standard conditions are 1 atmosphere (1013 mbar) and 298 degrees K. 13.NO3-Unc: the propagated uncertainty in nitrate concentration 14. SO4: Sulfate ion concentration. The units are micrograms of sulfate per standard cubic meter of air. Standard conditions are 1 atmosphere (1013 mbar) and 298 degrees K. 15.SO4-Unc: the propagated uncertainty in sulfate concentration 16. Oxalate: Oxalate ion concentration. The units are micrograms of oxalate per standard cubic meter of air. Standard conditions are 1 atmosphere (1013 mbar) and 298 degrees K. 17.Oxal-Unc: the propagated uncertainty in oxalate concentration 18. Na: Sodium ion concentration. The units are micrograms of sodium per standard cubic meter of air. Standard conditions are 1 atmosphere (1013 mbar) and 298 degrees K. 19.Na-Unc: the propagated uncertainty in sodium concentration 20. NH4: Ammonium ion concentration. The units are micrograms of ammonium per standard cubic meter of air. Standard conditions are 1 atmosphere (1013 mbar) and 298 degrees K. 21.NH4-Unc: the propagated uncertainty in ammonium concentration 22. K: Potassium ion concentration. The units are micrograms of potassium per standard cubic meter of air. Standard conditions are 1 atmosphere (1013 mbar) and 298 degrees K. 23.K-Unc: the propagated uncertainty in potassium concentration 24. Mg: Magnesium ion concentration. The units are micrograms of magnesium per standard cubic meter of air. Standard conditions are 1 atmosphere (1013 mbar) and 298 degrees K. 25.Mg-Unc: the propagated uncertainty in magnesium concentration 26. Ca: Calcium ion concentration. The units are micrograms of soluble calcium per standard cubic meter of air. Standard conditions are 1 atmosphere (1013 mbar) and 298 degrees K. 27.Ca-Unc: the propagated uncertainty in calcium concentration 28. NSS: Non-seasalt sulfate ion concentration, derived using sodium to correct for sea salt. The units are micrograms of sulfate per standard cubic meter of air. Standard conditions are 1 atmosphere (1013 mbar) and 298 degrees K. 29.NSS-Unc: the propagated uncertainty in non-seasalt sulfate concentration 30. ICSum: The sum of all mass concentrations for ions analyzed by IC. Note that this will certainly be smaller than the total ambient mass concentration, due to the exclusion of organics, soot, and insoluble minerals. The units are micrograms of carbon per standard cubic meter of air. Standard conditions are 1 atmosphere (1013 mbar) and 298 degrees K. 31. Cl-Pct: The percentage of total chloride (cone plus filter) that was on the TAS filter. 32. NO3-Pct: The percentage of total nitrate (cone plus filter) that was on the TAS filter. 33. SO4-Pct: The percentage of total sulfate (cone plus filter) that was on the TAS filter. 34. Oxal-Pct: The percentage of total oxalate (cone plus filter) that was on the TAS filter. 35. Na-Pct: The percentage of total sodium (cone plus filter) that was on the TAS filter. 36. NH4-Pct: The percentage of total ammonium (cone plus filter) that was on the TAS filter. 37. K-Pct: The percentage of total potassium (cone plus filter) that was on the TAS filter. 38. Mg-Pct: The percentage of total magnesium (cone plus filter) that was on the TAS filter. 39. Ca-Pct: The percentage of total calcium (cone plus filter) that was on the TAS filter. 40. NSS-Pct: The percentage of total non-seasalt sulfate (cone plus filter) that was on the TAS filter. 41. Comments. One sample was turned off briefly to avoid rain showers. This is Version 1.0 of the Huebert group TAS data. 5.0 Data Remarks The TAS data should be the most accurate (although perhaps not the most precise) measure of bulk anion and cation concentrations from the C-130. Since it eliminates any concern about modification of the ambient concentrations of any size particles by inlets, it should be free of biases either due to inlet losses or enhancement. The only concern is that it operated isokinetically, which we assured within a few percent throughout each sample. However, since each concentration is reached by extracting both a cone and a filter and subtracting a blank from each, the TAS data may well have lower precision than devices which analyze only a single filter, for instance. Two types of artifacts are of concern, both related to semivolatile species. If we collected ammonium nitrate aerosol, for example, there is a chance that some of the NH4NO3 would evaporate to nitric acid and ammonia after collection on the filter, thereby causing an underestimate of ammonium and nitrate aerosol. We think this is unlikely to be significant here, since virtually all of our MOUDI samples showed nitrate to be on coarse particles and ammonium to be on fine ones. Ammonium nitrate is a secondary aerosol that is usually in the accumulation mode. The other possible artifact is a positive one, due to the collection of acid gases on the filter or previously-collected particles. Since we used Teflon filters and Teflon-coated cones, we do not think that the sampling medium collected acid gases. It is possible, however, that alkaline dust on a filter could have collected either SO2 or nitric acid. Since sulfate was rarely on the same size as calcium, we doubt that SO2 was collected, but we cannot rule out the possibility that nitric acid had been adsorbed onto collected dust. It seems likely that this would have gone to completion in the atmosphere rather than on a filter, but we have no way of disproving the hypothesis that some observed nitrate was derived from nitric acid vapor that reacted on the filter with dust particles. Software compatibility The file TAS-C130Huebert16April02.txt is tab-delimited ACSII. It should import easily into spreadsheets or other programs. While it can be opened by conventional word processors, the long lines may cause a wrap that confuses the columns. (For the Mac, the application BBEdit Lite is able to handle long lines and huge files very quickly for various types of editing and viewing.) In Microsoft Office 98 Excel for the Mac click "File," "Open," highlight the file, and click "Open." Select "Delimited" when the Text Import Wizard window appears. Choose "Tab" delimiters, which should separate the columns nicely, then "Next." Depending on your use of the data, you may or may not wish to change the column formats prior to clicking "Finish." To import the file directly into Igor Pro, the line of units needs to be edited out. (If Igor sees non-numeric characters in the second line, it will make the whole column text and not recognize any numbers.) In Igor Pro, select "Data," "Load Waves," and "Load Delimited Waves." Then browse to the file, highlight it, and click "Open." The window that comes up should offer the proper wave names from the first row. Click "Make Table" to have the loaded waves appear as a table. Highlight wave names 0, 1, and 2, and set their format to "Text," to avoid having the data/time numbers changed to scientific exponential notation. Finally, click "Load" to finish the process.