----------------------------------------------------------------------------------- Readme file to accompany Environment Canada continuous tower data 2000-2008 v200908 ----------------------------------------------------------------------------------- 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 continuous 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 data sets report methane (CH4), carbon monoxide (CO) and carbon dioxide (CO2) mixing ratios collected at eight stations in Canada between 2000 and 2008. All methane and carbon monoxide 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 WMO CO for CO CO and CH4 Method: The continuous measurement of CH4 at Alert, Fraserdale, Candle Lake and Sable Island is currently being made using an Aglilent (formerly Hewlett Packard) gas chromatographs (Model 6890N)employing flame ionization detection. In November 1999, the CH4 gas chromatographic (Hewlett Packard 5890) system that was initially installed at Alert in September 1987 (along with the desk top integrator, data logger collection and automation software) was replaced with the Agilent 6890N GC. This system is fully automated via HP Chemstation software (described in the data section). A similar gas chromatographic system was installed at Fraserdale in October 2002, replacing the original HP 5890 GC that was installed in December 1990). At all sites, ambient air is delivered to the GC at approximately 5 L min-1 by a vacuum pump via a dedicated 0.95 cm o.d. sample line that extends to the top of a nearby tower. The air passes through a membrane filter, then through a pressure relief valve set at ~1 atmosphere to release excess pressure and is then dried to a dew point of around -60 degrees C by passing the air through a glass trap submerged in an -80 degree C methanol bath. All standard gases are supplied to the GC from pressurized gas cylinders equipped with high-purity, two-stage gas regulators. For CO and CH4, the analysis is done in a similar manner. CO and CH4 are first passed on to a 4'x1/8" pre-column (Molesieve 5a) and then passed on to 4'x1/8" analytical column (Unibeads 1s). The pre-column is back flushed allowing late eluting components and contamination to be passed back to the room. All columns are contained in the same oven and maintained at 80¡C. An electronic pressure controller is used to control the nitrogen carrier gas flow rate (~60 ml/min). CH4 elutes at ~2 minutess and CO at ~4 minutes after injection. After the CH4 elutes, a 1/16¡É 6-port two-position valve is switched, allowing the CO to pass through a heated Nickel catalyst. The catalyst converts the CO to CH4, permitting the analysis of CO to be done on the FID. The shunting configuration also avoids having the oxygen to pass through the catalyst, thus eliminating potential contamination as well as a large air peak that can cause baseline irregularities to occur near the CH4 peak. Measurement cycles consist of repeated series of standard gas and ambient air injections. The peak height for the standard injection is used to calculate the CH4 mole fraction of the ambient injections. All CH4 measurements at Alert and Fraserdale are reported in nmole mole-1 (abbreviated ppm, or parts per million, mole fraction), dry air,relative to the NOAA04 CH4 standard scale. Analytical precision based on replicate injections for standard tank gas is approximately 1.5 ppb for CH4 and 2 ppb for CO. CO2 Method: The continuous measurement of CO2 at Fraserdale, Alert, Candle Lake and Sable Island follow the set of principles and protocols set by the WMO based on non-dispersive infrared (NDIR) methodology methodology [Trivett and Kohler, WMO Report No. 134]. A standardize protocol is applied at all stations making continuous measurments (implemented at Alert and Fraserdale in 2000). Implemented at the start of the programs at Candle Lake and Sable Island in 2003. The objectives of the new protocol are: 1) To increase the lifetime of our working standard tanks from ~9 months to ~ 4 years, 2) To reduce the number of levels in our central calibration hierarchical scheme from 6 to 3 levels, 3) To permit a larger atmospheric measurement range to be covered, 4) To provide final data in near real time, 5) To eliminate the time involved with reprocessing the historical data because of drifts in either calibration tanks or scale. The specifics of the new measurement procedure are as follows: 1) At each site, 11 standard tanks are used; 5 station tanks (~350, 365, 380,395 and 410 ppm), 4 working tanks (~355, 370, 385 and 400 ppm), one target tank (~365 ppm) and one zero tank (~340 ppm). 2) The 5 station tanks are calibrated approximately every 6 months against a set of 5 transfer standards that are transported between the sites and the central laboratory in Toronto. 3) The working and target tanks are automatically calibrated every 11 days against the 5 station tanks. The station tanks have a lifespan more than 20 years. 4) The target and zero tanks are passed through the analyzer for 5 minutes each at the top of every hour. The working tanks are sequentially passed through the analyzer (for 5 minutes each) every 5 hours after the hourly target and zero tanks have been passed through the system. The 5-hour time span of the working tanks results in a life span for these tanks of approximately 4 years. The target and zero tanks have life spans of ~9 and 3 months respectively. A Campbell Scientific (Model CR21x) data logger is used to control the automated injection sequence and processes 5 minute averaged data records generated from the 1 second output signal voltages from the NDIR analyzer. The data logger also collects auxiliary data information on temperatures, pressures and flow rates. A local server collects the data from the logger and makes it available via FTP to the server at the in Toronto. Stations covered by the accompanying data sets: Alert (ALT) (82deg 27min N; 62deg 31min W; 210 masl) Candle Lake (CDL) (53deg 59min N; 105deg 07min W; 489 masl) East Trout Lake (ETL) (54deg 21min N; 104deg 59min W; 493 masl) Egbert (EGB) (44deg 22min N; 79deg 07min W; 251 masl) Fraserdale (FDL) (49deg 53min N; 81deg 34min W; 210 masl) Sable Island (WSA) (43deg 56min N; 60deg 01min W; 5 masl) Chibougamou (CHM) (49deg 41min N; 74deg 18min W; 393 masl) Lake Labiche (LLB) (54deg 57min N; 112deg 27min W; 540 masl) 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 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"