ALBERT

Description: Three years of greenhouse gases measurements, obtained using a gas chromatograph (GC) system located at the Puy de Dôme station at 1465 m a.s.l. in Central France are presented. The GC system was installed in 2010 at Puy de Dôme and was designed for automatic and accurate semi-continuous measurements of atmospheric carbon dioxide, methane, nitrous oxide and sulfur hexafluoride mole fractions. We present in detail the instrumental set up and the calibration strategy, which together allow the GC to reach repeatabilities of 0.1 μmol mol−1, 1.2, 0.3 nmol mol−1 and 0.06 pmol mol−1 for CO2, CH4, N2O and SF6, respectively. Comparisons of the atmospheric time series with those obtained using other instruments shown that the GC system meets the World Meteorological Organization recommendations. The analysis of the three-year atmospheric time series revealed how the planetary boundary layer height drives the mole fractions observed at a mountain site such as Puy de Dôme where air masses alternate between the planetary boundary layer and the free troposphere. Accurate long-lived greenhouse gases measurements collocated with 222Rn measurements as an atmospheric tracer, allowed us to determine the CO2, CH4 and N2O emissions in the catchment area of the station. The derived CO2 surface flux revealed a clear seasonal cycle with net uptake by plant assimilation in the spring and net emission caused by the biosphere and burning of fossil fuel during the remainder of the year. We calculated a mean annual CO2 flux of 1150 t(CO2) km−2. The derived CH4 and N2O emissions in the station catchment area were 5.6 t(CH4) km−2 yr−1 and 1.5 t(N2O) km−2 yr−1, respectively. Our derived annual CH4 flux is in agreement with the national French inventory, whereas our derived N2O flux is five times larger than the same inventory.

Description: This study presents two methods for estimating methane emissions from a waste water treatment plant (WWTP) along with results from a measurement campaign at a WWTP in Valence, France. These methods, chamber measurements and tracer release, rely on Fourier Transform Infrared (FTIR) spectroscopy and Cavity Ring Down Spectroscopy (CRDS) instruments. We show that the tracer release method is suitable to quantify facility- and some process-scale emissions, while the chamber measurements, provide insight into individual process emissions. Uncertainties for the two methods are described and discussed. Applying the methods to CH4 emissions of the WWTP, we confirm that the open basins are not a major source of CH4 on the WWTP (about 10% of the total emissions), but that the pretreatment and sludge treatment are the main emitters. Overall, the waste water treatment plant represents a small part (about 1.5%) of the methane emissions of the city of Valence and its surroundings, which is lower than the national inventories.

Description: This paper describes different methods to estimate methane emissions at different scales. These methods are applied to a waste water treatment plant (WWTP) located in Valence, France. We show that Fourier Transform Infrared (FTIR) measurements as well as Cavity Ring Down Spectroscopy (CRDS) can be used to measure emissions from the process to the regional scale. To estimate the total emissions, we investigate a tracer release method (using C2H2) and the Radon tracer method (using 222Rn). For process-scale emissions, both tracer release and chamber techniques were used. We show that the tracer release method is suitable to quantify facility- and some process-scale emissions, while the Radon tracer method encompasses not only the treatment station but also a large area around. Thus the Radon tracer method is more representative of the regional emissions around the city. Uncertainties for each method are described. Applying the methods to CH4 emissions, we find that the main source of emissions of the plant was not identified with certainty during this short campaign, although the primary source of emissions is likely to be from solid sludge. Overall, the waste water treatment plant represents a small part (3%) of the methane emissions of the city of Valence and its surroundings,which is in agreement with the national inventories.

Description: Results from the Trainou tall tower measurement station installed in 2006, are presented for atmospheric measurements of CO2, CH4, N2O, SF6, CO, H2 mole fractions and Radon-222 activity. Air is sampled from four sampling heights (180 m, 100 m, 50 m and 5 m) of the Trainou 200 m television tower in the Orléans forest in France (47°57'53'' N, 2°06'45'' E, 131 m a.s.l.). The station is equipped with a custom-build CO2 analyzer (CARIBOU), which is based on a commercial NDIR analyser (Licor 6252), and a coupled gas chromatographic GC system equipped with ECD and FID (HP6890N, Agilent) and a reduction gas detector (PP1, Peak Performer). Air intakes, pumping and air drying system are shared between the CARIBOU and the GC systems. After some initial problems, we achieved short-term repeatability (1 sigma, over several days) for the GC system of of 0.05 ppm for CO2, 1.4 ppb for CH4, 0.25 ppb for N2O, 0.08 ppb for SF6, 0.88 ppb for CO and 3.8 for H2. The repeatability of the CARIBOU CO2 analyser is 0.06 ppm. In addition to the in-situ measurements, weekly flask sampling is performed, and flask air samples are analysed at the LSCE central laboratory for the same species as well for stable isotopes of CO2. The comparison between in-situ measurements and the flask sampling showed averaged differences of 0.08 ± 1.4 ppm CO2, 0.69 ± 7.3 ppb CH4, 0.64 ± 0.62 ppb N2O, 0.01 ± 0.1 ppt SF6 and 1.5 ± 5.3 ppb CO for the years 2008–2012. At Trainou station, the mean annual increase rates from 2007 to 2011 at the 180 m sampling height were 2.2 ppm yr−1 for CO2, 4 ppb yr−1 for CH4, 0.78 ppb yr−1 for N2O and 0.29 ppt yr−1 for SF6 respectively. For all species the 180 m sampling level showed the smallest diurnal variation. Mean diurnal gradients between the 50 m and the 180 m sampling level reached up to 30 ppm CO2, 15 ppm CH4 or 0.5 ppb N2O during night whereas the mean gradients are smaller than 0.5 ppm for CO2 and 1.5 ppb for CH4 during afternoon.

Description: Tropospheric column-averaged CH4 mole fractions were derived from ground-based absorption columns measurements. The method used stratospheric N2O columns to correct for the stratospheric contribution to the CH4 total column. The method was applied to four TCCON sites covering locations from the Northern Arctic to the tropics. It performs well for all sites. The derived tropospheric CH4 concentrations were compared with profiles measured by aircraft at three sites. The results indicate an inter-site consistency within 6 ppb (~ 0.3%). With aircraft profiles up to 3 km, the seasonal behavior of the derived tropospheric CH4 concentration was also checked. It reveals a difference of 20 ppb around. The mean relative uncertainty of the four sites is 0.23%. Comparing with the method using HF the proposed method shows a smaller relative uncertainty and less H2O dependence.

Description: Over the last few decades, in-situ measurements of atmospheric N2O mole fractions have been performed using gas chromatographs (GCs) equipped with electron capture detectors (ECDs). When trying to meet the World Meteorological Organization's (WMO) quality goal, this technique becomes very challenging as the detectors are highly non-linear and the GCs at remote stations require a considerable amount of maintenance by qualified technicians to maintain good short-term and long-term repeatability. With more robust optical spectrometers being now available for N2O measurements, we aim to identify a robust and stable analyzer that can be integrated into atmospheric monitoring networks, such as the Integrated Carbon Observation System (ICOS). In this study, we tested seven analyzers that were developed and commercialized from five different companies and compared the results with established techniques. Each instrument was characterized during a time period of approximately eight weeks. The test protocols included the characterization of the short-term and long-term repeatability, drift, temperature dependence, linearity and sensitivity to water vapor. During the test period, ambient air measurements were compared under field conditions at the Gif-sur-Yvette station. All of the analyzers showed a standard deviation better than 0.1 ppb for the 10 min averages. Some analyzers would benefit from improvements in temperature stability to reduce the instrument drift, which could then help in reducing the frequency of calibrations. For most instruments, the water vapor correction algorithms applied by companies are not sufficient for high-precision atmospheric measurements, which results in the need to dry the ambient air prior to analysis.