Three years of semicontinuous greenhouse gas measurements at the Puy de Dôme station (central France)

M. Lopez,J.-L. Bonne,M. Ramonet,J.-M. Pichon,A. Colomb,P. Laj,V. Kazan,M. Schmidt

doi:10.5194/amt-8-3941-2015

Abstract

Abstract. Three years of greenhouse gas 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 semicontinuous measurements of atmospheric carbon dioxide, methane, nitrous oxide and sulfur hexafluoride mole fractions. We present in detail the instrumental setup and the calibration strategy, which together allow the GC to reach repeatabilities of 0.1 μmol mol−1, 1.2 nmol mol−1, 0.3 nmol mol−1 and 0.06 pmol mol−1 for CO2, CH4, N2O and SF6, respectively. The analysis of the 3-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 gas 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 1310 ± 680 t CO2 km−2. The derived CH4 and N2O emissions in the station catchment area were 7.0 ± 4.0 t CH4 km−2 yr−1 and 1.8 ± 1.0 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 5 times larger than the same inventory.

Highlights

The release of anthropogenic greenhouse gases (GHGs) into the atmosphere leads to a modification of their natural cycles and to a strong increase in atmospheric radiative forcing (Myhre et al, 2013)
We present in detail the instrumental setup and the calibration strategy, which together allow the gas chromatograph (GC) to reach repeatabilities of 0.1 μmol mol−1, 1.2 nmol mol−1, 0.3 nmol mol−1 and 0.06 pmol mol−1 for CO2, CH4, N2O and SF6, respectively
The analysis of the 3-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

Summary

Introduction

The release of anthropogenic greenhouse gases (GHGs) into the atmosphere leads to a modification of their natural cycles and to a strong increase in atmospheric radiative forcing (Myhre et al, 2013). To limit the global temperature rise, most industrialized countries signed the “United Nations Framework Convention on Climate Change” (UNFCCC) treaty in 1992 to stabilize their GHG emissions between 1990 and 2000 and it entered into force in 1994. This convention was enhanced by the Kyoto Protocol, which was signed in 1997 and was ratified by 182 countries. The EU aims to reduce its total GHG emissions by 20 % in 2020, relative to emissions in 1990 Despite this commitment, it is extremely difficult to validate the surface GHG fluxes on the country scale using a reliable, transparent method

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