------------------------------------------------------------------------------- Readme file to accompany Environment Canada flask tower data 2000-2008 v201009 ------------------------------------------------------------------------------- TERMS AND CONDITIONS (Adapted from NOAA and NACP data policy) ------------------------------------------------------------- CITATION INFORMATION Use of these data in any part implies an agreement on the part of the user that individuals and/or institutions responsible for contributing to data sets used must be specifically cited in addition to a general citation of the NACP greenhouse gas database. The Environment Canada flask tower data set should be cited as follows: Doug Worthy Environment Canada 4905 Dufferin Street. Toronto, Ontario. NACP investigators will include an acknowledgement in each publication or presentation arising from participation in NACP. The wording shall be similar to the following: "This study was part of the North American Carbon Program." Data providers and funding agencies may request additional acknowledgements. Upon publication of results, investigators should send the NACP Office an electronic copy of the publication. USE OF DATA These data are made freely available to the public and the scientific community in the belief that their wide dissemination will lead to a greater understanding and new scientific insights. The availability of these data does not constitute publication of the data. We rely on the ethics and integrity of the user to assure that the source(s) receive fair credit for their work. If the data are obtained for potential use in a publication or presentation, the source(s) should be informed at the outset of the nature of this work. If the source's data are essential to the work, or if an important result or conclusion depends on their data, co-authorship may be appropriate. This should be discussed at an early stage in the work. Manuscripts using the source's data should be sent to the source(s) for review before they are submitted for publication so we can ensure that the quality and limitations of the data are accurately represented. RECIPROCITY AGREEMENT Use of these data implies an agreement to reciprocate. Laboratories making similar measurements agree to make their own data available to the general public and to the scientific community in an equally complete and easily accessible form. Modelers are encouraged to make available to the community, upon request, their own tools used in the interpretation of the source data, namely well documented model code, transport fields, and additional information necessary for other scientists to repeat the work and to run modified versions. Model availability includes collaborative support for new users of the models. GENERAL -------- The accompanying flask data sets report methane (CH4) and carbon dioxide (CO2) mixing ratios collected at seven stations in Canada between 2000 and 2008. All methane measurements included in the accompanying data files were by gas chromatography flame ionization detector systems (FID, Agilent 6890N); all carbon dioxide measurements in the accompanying data files were taken by nondispersive infrared sensor (NDIR, Siemens U3) systems. Reported mixing ratios for continuous data are based on hourly averages calibrated using: WMO mole fraction scale for CO2. NOAA04 Scale for CH4 CH4 Method: In 1997, an automated flask analysis system was developed and flask samples collected at Alert, Sable Island and Estevan Point for CO2 begun being analyzed for methane as well as for nitrous oxide, sulphur hexafluoride, carbon monoxide and Hydrogen. A pair of air samples are collected approximately weekly in two 2L glass flasks. The flasks have dual glass barreled valves with VitonR o-ring seals. Using a pumping unit, the flasks are first flushed and then filled in parallel to 15psi with a pump. The sampling line extends to the top of nearby towers. A samples are analyzed for CH4 at Environment Canada in Toronto by a gas chromatography equipped with an Flame Ionization Detector. Ambient and standard gas samples are bracket by 2 working tanks. Instrument response of the sample are compared to two standards of known CH4 content. Measurements are reported in units of nanomol/mol (10^-9 mol CH4 per mol of dry air (nmol/mol) or parts per billion (ppb)) relative to the NOAA04 CH4 standard scale. Further details on the flask collection/program can be found in the CO2 section below. CO2 Method: Environment Canada initially used evacuated 2 L glass flasks fitted with 6 mm bore high vacuum stopcocks (lubricated with Apiezon-N grease) at Alert, Sable Island and Cape St. James. A new flask type with a glass barreled valve with VitonR o-ring seals was introduced at Alert and Estevan Point in 1992. It is more robust for field sampling and easier to open in extreme cold temperatures than the greased stopcock flasks. EC introduced a third flask type into its sampling network at Alert and Estevan Point in 1993 and at Sable Island in June 2003. This flask has dual glass barreled valves with VitonR o-ring seals. Using a pumping unit, this flask is flushed and filled inside the laboratory to 15 psi with air drawn in from a sampling line extending to the top of nearby towers. In 1988, EC assumed responsibility for the flask programs at Alert, Cape St. James, and Sable Island from the Insitute of Ocean Sciences, British Columbia. The analyses were initially made using a Hartman and Braun URAS-3E analyzer. In October 1989, the analyzer was changed to a Maihak UNOR-6N. All analyses were made using CO2-in-air reference gases. Three CO2 standard gases (340 ppm, 355 ppm and 365 ppm) and a reference gas (330 ppm) were used on the analysis system. The mixing ratios of the standard gases were calibrated at EC. The Environment Canada CO2 flask analysis system was designed to analyze a maximum of eight flasks per run. An 8-port stream selection valve was used to switch between flasks while a vacuum pump (KNF Neuberger pump, Model UN022-SV1) was used to extract the air from the flasks. The three calibration gases and eight flasks were switched manually. A Campbell Scientific CR21x data logger was used to collect the raw data. All measurements were made on a dry air basis, with both sample and reference gas air streams passing through stainless steel traps (t inch diameter) submerged in a methanol bath at t55o C. Only one aliquot was extracted and analyzed from each flask. A typical flask run sequence consisted of the calibration gases (C1 to C3), followed by eight flasks, and again followed by the calibration gases (C1 to C3). For each run, the voltages of the calibration gases, before and after the flasks, were averaged. The averaged voltages and mixing ratios assigned to the calibration gases were used to generate a quadratic system response function for the run. The mixing ratios for the flasks were calculated by substituting the flask voltages into the system response function for each flask run. Minimal or no drifts were observed in the bracketing voltages of the calibration gases. Changes were made to the flask analysis system in April 1991. The UNOR-6N analyzer was replaced with a Siemens Ultramat III analyzer. The change in analyzer was necessary because the UNOR-6N was sensitive to subtle changes in sample flow, which occurred even though mass flow controllers were used. Because the Siemens analyzer had a larger sample cell volume (100 cm3) compared to the UNOR-6N analyzer (8 cm3), it was necessary to increase the flushing volume from each flask. The system was modified for static measurements to compensate for the extra volume required for flushing. To achieve static measurements, the system is flushed with gas and then a solenoid valve shuts off the gas flow to the sample cell. The gas in the sample cells equilibrates to ambient pressure before a measurement is taken. Static measurements require less gas from a given flask. Changes to the system included the addition of a 10-port stream selection valve, a target gas (350-360 ppm), two additional calibration gases (340-380 ppm), and a solenoid valve upstream of the sample cell. The reference gas, five calibration gases, target gas, and the outlet of the flask stream selection valve were connected to the 10-port valve. At present, a typical flask run has the following sequence: reference, calibration gases (C1-C5), reference, target, flasks (F1-F8), reference, calibration gases (C1-C5), reference and target. Prior to running the flask analysis system on any given day, the regulators on the reference tanks, calibration tanks and target tanks are flushed with about 3 L of gas. The gas is also passed through the system to stabilize the analyzer. To extract air from the ambient pressure flasks, an automated sequence is programmed into the data logger to control 1) the switching of the stream selection valves, 2) the opening and closing of the solenoid and 3) turning the pump on and off. The data logger also collects the raw data and calculates the average and standard deviation voltages for each sample. Stations covered by the accompanying flask data sets: Alert (ALT) (82deg 27min N; 62deg 31min W; 210 masl) Estevan Point (ESP) (49deg 35min N; 126deg 22min W; 39 masl) Sable Island (WSA) (43deg 56min N; 60deg 01min W; 5 masl) All methane measurements included in the accompanying data files were made by gas chromatography systems; all carbon dioxide measurements in the accompanying data files were made by nondispersive infrared sensor (NDIR) systems. Reported mixing ratios are based on hourly averages calibrated using the WMO mole fraction scale. Sample collection times for flasks were rounded to the nearest minute. VARIABLE NAMES -------------- YYYYMMDD : Year, month, and day of sampling. doy : Absolute day of year UTC : Coordinated Universal Time, in seconds from midnight station : Three letter code, based on NOAA station ID system, identifying station where measurements were collected. latitude : Latitude, in degrees longitude : Longitude, in degrees altitude : Altitude, in meters airT.C : Air temperature, in degrees Celsius press : Atmospheric pressure, in mbar rel.humid : Relative Humidity, in percent wind.d : Wind direction, in degrees wind.m : Wind speed, in meters per second CH4_FID : Methane mixing ratio, in ppb ND.CH4 : Number of data points used in hourly methane average SD.CH4 : Standard deviation of methane mixing ratios used in hourly averages CO_FID : Carbon monoxide mixing ratio, in ppb ND.CO : Number of data points used in hourly carbon monoxide average SD.CO : Standard deviation of carbon monoxide mixing ratios used in hourly averages CO2_NDIR : Carbon dioxide mixing ratio, in ppm ND.CO2 : Number of data points used in hourly carbon dioxide average SD.CO2 : Standard deviation of carbon dioxide mixing ratios used in hourly averages MISSING VALUES -------------- For files in .RData format, missing values are represented by "NA". For files in .csv format, missing values are represented by "NaN"