Póster presentado en: 16th WMO/IAEA Meeting on Carbon Dioxide, Other Greenhouse Gases, and Related Measurement Techniques celebrado del 25 al 28 de octubre de 2011 en Wellington, Nueva Zelanda

Campo Hernández, Rubén del

Conway, T. J.

Dlugokencky, Edward J.

Gómez Peláez, Ángel Jesús

Gómez-Trueba, Vanessa

Ramos López, Ramón

English

Agencia Estatal de Meteorología

New improvements in the Izaña (Tenerife, Spain) global GAW station in-situ greenhouse gases measurement programA.J. Gomez-Pelaez1, R. Ramos1, V. Gomez-Trueba1,2, R. Campo-Hernandez1, E. Dlugokencky3, and T. Conway31 Izaña Atmospheric Research Center, Meteorological State Agency of Spain (AEMET)2 Air Liquide Canarias3 NOAA-ESRL-GMDPresented at “16th WMO/IAEA Meeting onCarbon Dioxide, Other Greenhouse Gases, andRelated Measurement Techniques” (Wellington, New Zealand, October 25-28, 2011) ”Contact e-mail:  agomezp@aemet.esCO2                                                               CH4 N2O                                                               SF6ABCDReferences  Gomez-Pelaez, A.J., Ramos, R., Gomez-Trueba, V., Gonzalez, Y., Campo-Hernandez, R., Novelli, P., "In-situ CO measurements at Izaña global GAW station: GC-RGA system, data processing, and 2008-2011 time series”, presented at “16th WMO/IAEA Meeting on Carbon Dioxide, Other Greenhouse Gases, and Related Measurement Techniques” (Wellington, New Zealand, October 25-28, 2011)” , to be published in a peer-review paper in 2012 Gomez-Pelaez, A.J., Ramos, R., "Improvements in the Carbon Dioxide and Methane Continuous Measurement Programs at Izaña Global GAW Station (Spain) during 2007-2009", in GAW report (No. 194) of the “15th WMO/IAEA Meeting of Experts on Carbon Dioxide, Other Greenhouse Gases, and Related Tracer Measurement Techniques (Jena, Germany; September 7-10, 2009)”, edited by Willi A. Brand, World Meteorological Organization (TD No. 1553), 133-138, 2011 Gomez-Pelaez, A.J., Ramos, R., "Installation of a new gas chromatograph at Izaña GAW station (Spain) to measure CH4, N2O, and SF6" in GAW Report (No. 186) of the "14th WMO/IAEA meeting of experts on Carbon dioxide, other greenhouse gases, and related tracers measurement techniques (Helsinki, Finland, 10-13 September 2007)", edited by Tuomas Laurila, World Meteorological Organization (TD No. 1487), 55-59, 2009 Gomez-Pelaez, A.J., Ramos, R., Perez-delaPuerta, J., “Methane and carbon dioxide continuous measurements at Izaña GAW station (Spain)”, in GAW Report (No. 168) of the “13th WMO/IAEA Meeting of Experts on Carbon Dioxide Concentration and Related Tracers Measurement Techniques (Boulder, Colorado, USA, 19-22 September 2005)”, edited by J.B. Miller, World Meteorological Organization (TD No. 1359), 180-184, 2006. Scheel, H.E. (2009), System and Performance Audit for Nitrous Oxide at the Global GAW Station Izaña, Tenerife, Spain, November 2008, WCC-N2O Report 2008/11, http://www.aemet.izana.org/publications/Rep_WCCN2O_2008_IZOAudit.pdf Zellweger, Christoph, et al. (2009), System and Performance Audit of Surface Ozone,Carbon Monoxide, Methane and Nitrous Oxide at the Global GAW Station Izaña, Spain, March 2009, WCC-Empa Report 09/1, http://gaw.empa.ch/audits/IZO_2009.pdf Comparison between flask and continuous measurements  We have developed a Fortran90 numerical code to compare in-situ continuous measurements with simultaneous collocated NOAA flask samples. The inputs of the programme are hourly mean in-situ data files (in the old WDCGG format) and a NOAA flask data file (NOAA format). The comparison has the following novel characteristics:   Only flasks with the flags “…” or “..P” are accepted. Also, both members of the pair must be present. Each pair is substituted by the mean (fm) and the standard deviation (sdf) of the 2 flasks that compose the pair.  Each pair is compared with the hourly mean (hm) simultaneous in time (the hourly mean time interval must contain the time of the pair sampling). The standard deviation (sdh) of the sample of measurements used to compute the hourly mean is also taken into account.  The difference fm-hm and its “internal” standard uncertainty, SQRT(sdh*sdh+sdf*sdf), are computed for every member of the comparison set. Their time series for each trace gas are showed in graphics B (in the array of figures), where the x-axis is lotus time.  For each trace gas, global and annual difference means and standard deviations are computed. 3 types of means (and standard deviations) are computed: Mean, WMean, and FWMean (as denoted in graphics D). Mean is the conventional mean. FWMean is a “full” weighted mean computed using the minimum variance method (maximum likelihood for Gaussian distributions). WMean is an “intermediate” weighted mean. A complete description of this method is given by Gomez-Pelaez et al. (2012) and its associated per-review paper. The basic idea is: differences with a larger uncertainty provide information of a lower quality to compute de mean.  Annual means are plotted in graphics D. Global means and their standard deviations have the following values:   Mean St. dev. WMean St. dev. FWMean St. dev. CO2 (ppm) 0.05 0.66 0.07 0.52 0.09 0.49 CH4 (ppb) -1.1 17.7 0.9 11.4 -0.8 7.1 N2O (ppb) 0.07 0.47     SF6 (ppt) 0.0002 0.07      Novelties in the CH4 program  See Gomez-Pelaez & Ramos (2011) and references therein for a description of this measurement program. On March 2009, Izaña’s CH4 program passed satisfactorily a WCC-EMPA scientific audit; see Zellweger et al. (2009).  A dilution correction (depending on bath temperature), due to the presence of a very small amount of remaining water vapour in the sample after cryocooling, has been implemented in CH4 and N2O data (re)processing for measurements carried out after June 14, 2007. See Gomez-Pelaez & Ramos (2009) for a conceptual description of this correction. As examples, for a CH4 mole fraction of 1850 ppm, the correction amounts to 0.82 ppb and 0.17 ppb for cryocool bath temperatures of -31ºC and -45ºC, respectively. Bath temperature usually has been -70ºC or smaller since April 2009, being the dilution correction negligible most of the time since then.      For the period April 26, 2006 (lotus time in days: lt0=38,833.64) till May 28, 2008 (lotus time in days: ltf=39,596.42), a significant systematic deviation has been appreciated when comparing continuous in-situ CH4 data with collocated NOAA flasks (weekly sampling). The reasons of such deviation are still not known. For such period, we have added a cubic (in time) correction to the continuous in-situ data, being the correction in ppb: -2.556 x 10-7 x t3 + 4.042 x 10-4 x t2 – 0.1477 x t –14.08, where t=lt-lt0, and lt is lotus time in days. Abstract  We present the main improvements in the in-situ Izaña (Global GAW station) greenhouse gases (GHGs) measurement program during the last few years. First, we present the calibration schemes for the GC-ECD used to measure atmospheric N2O and SF6, their calibration processing and statistics, and the software developed for ambient data processing taking into account the hierarchy of calibrations. Also, the in-situ Izaña N2O and SF6 series (from June 2007 till July 2011) are showed. Second, we present the software developed to compare in-situ Izaña GHG measurements with co-located NOAA flasks, and summarizes the results of such comparisons for CO2, CH4 , N2O and SF6. Third, some novelties concerning the in-situ Izaña CH4 measurements are detailed. Finally, updates of the in-situ CO2 and CH4 Izaña time series are showed. Figure 1Figure 2We have developed Fortran90 numerical codes to process calibrations, and ambient data, taking into account the hierarchy of calibrations. We sketch briefly such processing.   Each calibration has 5 cycles. Mean h/hwt and sample standard deviation are computed for each standard level. The coefficients of the response function are obtained through least-squares fitting to the h/hwt means. Once the coefficients are known, the N2O response function is rewritten as: 22 )()(1 wtwtwt rrarrslopehh −+−+=  , where slope=a1+2a2rwt, rwt is the working gas mole fraction (the solution of the response function for h/hwt =1), and a0, a1, and a2 are the coefficients of the quadratic polynomial, being the sub-index the power of the accompanying mole fraction in the polynomial. Figures 1 and 2 show the rwt determined in the calibrations, and the RMS (as error bars) of the fitting residuals, where the Mean Square is computed as the square residuals summatory divided by 2 or by 3 (for N2O or SF6, respectively), the effective number of degrees of freedom(instead of 5, the standard levels).  The time dependent GC-ECD response function, for the working gas in use, is computed from the response functions determined in the calibrations. For SF6, rwt and slope are computed as the mean of the values obtained in the calibrations. For N2O, slope and a2 are computed as the mean of the calibration values; whereas a linear drift in time is allowed for rwt (Snedecor’s F tests are used, as described by Gomez-Pelaez & Ramos 2011).  For ambient measurements, discarding of outliers is done in a similar way as in Gomez-Pelaez et al. (2006) for CH4; firstly for the hwt /rwt time series, and finally for the ambient air mole fraction series.     Dilution correction is applied for N2O (see bellow, the second paragraph of the section “Novelties in the CH4 program” of this presentation).  A correction, due to a small bias in the ambient air inlet line, is applied to N2O mole fraction. Such bias has been accurately determined using 8 working tanks filled with ambient air at Izaña station. The physical reason of the bias is being investigated.  Graphics A (in the array of figures) show updated daily night means (20:00-08:00 UTC) of Izaña in-situ CO2 , CH4 , N2O, and SF6 atmospheric measurements. N2O and SF6 calibration and ambient data processing  Izaña’s N2O measurement program passed satisfactorily a scientific audit carried out by WCC-N2O in November 2008; see Scheel (2009). Gomez-Pelaez & Ramos (2009) describes the system to measure N2O and SF6 at Izaña station (GC-ECD system configuration, time sequences, and chromatograms), but there have been some changes:    We have changed the method for locating peak baselines, considering SF6 as a tangent peak far on the tail of the N2O peak (instead of forcing a valley baseline), and have reintegrated the full series of chromatograms.   The one hour injection cycle for ambient air measurements, described in Table 2 of that reference, was in operation till November 3, 2008. Since such date, the injection cycle lasts 15 minutes: working gas (minute 00:00), ambient air (minute 07:30).  The calibration basic cycle was changed on November 3, 2008. Before such date, it was st1-st2-st3-st4-st5-wt1-wt2-wt1; after that date, it has been wt-st1-wt-st2-wt-st3-wt-st4-wt-st5; where wt indicates working gas, and st indicates standard gas.  We work with the ratio h/hwt: peak height relative to working gas peak height (interpolating bracketing working gas injections). The response function used assumed that h/hwt is a quadratic polynomial in N2O mole fraction, and a linear polynomial in SF6 mole fraction. Calibrations are carried out every 2 weeks. Processing them, response functions, working gas mole fractions, and uncertainties are obtained. 

New improvements in the Izaña (Tenerife, Spain) global GAW station in-situ greenhouse gases measurement program

https://repositorio.aemet.es/bitstream/20.500.11765/7775/1/CIAI_AEMET_Poster_GGMT2011.pdf

New improvements in the Izaña (Tenerife, Spain) global GAW station in-situ greenhouse gases measurement program

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