C. Yver

Inverse modeling of European CH4 emissions 2001-2006

European CH4 emissions are estimated for the period 2001-2006 using a four-dimensional variational (4DVAR) inverse modeling system, based on the atmospheric zoom model TM5. Continuous observations are used from various European monitoring stations, complemented by European and global flask samples from the NOAA/ESRL network. The available observations mainly provide information on the emissions from northwest Europe (NWE), including the UK, Ireland, the BENELUX countries, France and Germany. The inverse modeling estimates for the total anthropogenic emissions from NWE are 21% higher compared to the EDGARv4.0 emission inventory and 40% higher than values reported to U.N. Framework Convention on Climate Change. Assuming overall uncertainties on the order of 30% for both bottom-up and top-down estimates, all three estimates can be still considered to be consistent with each other. However, the uncertainties in the uncertainty estimates prevent us from verifying (or falsifying) the bottom-up inventories in a strict sense. Sensitivity studies show some dependence of the derived spatial emission patterns on the set of atmospheric monitoring stations used, but the total emissions for the NWE countries appear to be relatively robust. While the standard inversions include a priori information on the spatial and temporal emission patterns from bottom-up inventories, a further sensitivity inversion without this a priori information results in very similar NWE country totals, demonstrating that the available observations provide significant constraints on the emissions from the NWE countries independent from bottom-up inventories.

Strong similarities between night-time deposition velocities of carbonyl sulphide and molecular hydrogen inferred from semi-continuous atmospheric observations in Gif-sur-Yvette, Paris region

We investigated the diurnal variations of atmospheric carbonyl sulphide (COS) during 2011 at Gif-sur-Yvette, a suburban atmospheric measurement site in France. These data were collected semi-continuously in parallel with hydrogen (H2), carbon monoxide (CO) and 222Radon (222Rn) measurements. Fluxes and deposition velocities were calculated for nocturnal situations of low boundary layer height using the Radon-Tracer Method. Contrary to CO and H2, the diurnal cycles of COS are not impacted by emissions from nearby automobile traffic. In the absence of local anthropogenic combustion sources, COS and H2 mole fractions generally show similar temporal variations with night-time depletion coinciding with 222Rn accumulation during stable nocturnal conditions. Nocturnal COS deposition velocities range from 0.07 to 0.40 mm s−1, with an annual mean of 0.18±0.12 mm s−1 (n=14). We found strong similarities between COS and H2 dry deposition velocities in terms of annual mean and ranges of variation, and data showed linear correlation between the two. This study provides new evidence of the loss of COS near the ground via non-photosynthetic processes. Although the dominant sink of atmospheric H2 is diffusion and subsequent destruction in soils, it is not all certain that COS is taken up at night solely by soils.

Measurements of molecular hydrogen and carbon monoxide on the Trainou tall tower

We present 2 yr (October 2008 to September 2010) of in situ measurements of molecular hydrogen (H2) and carbon monoxide (CO) sampled at the tall tower of Trainou, France (47.96°N, 02.11°E, 131 masl, sampling height: 50, 100 and 180 m). Radon-222 (222Rn) measurements were added in May 2009. Background seasonal cycles, based on afternoon values, exhibit an amplitude of 45 and 60 ppb for H2 and CO, respectively, for the three different heights (50, 100 and 180 m above ground). The vertical gradient also shows seasonal variations with a maximum (during the night) of 20 and 45 ppb for H2 and CO, respectively.We also observe diurnal cycles for H2 and CO for the three different heights. In the afternoon, the mixing ratios at the three different heights are similar and are comparable with maritime background stations, such as Mace Head (Ireland). The diurnal cycle of 222Rn follows the boundary layer height variations, with maximum values in the morning. Throughout the year but especially in summer and autumn, the H2 mixing ratio shows nighttime depletion, with the lowest values at 06:00 UTC, due to soil uptake and the low boundary layer height. Using a simple box approach and the Radon-Tracer-Method, the H2 deposition velocity is calculated for the catchment area of Trainou.We find a mean value for the H2 deposition velocity of 2.6 ± 0.9 10-2 cm-2 s-1. During wintertime, H2 and CO are sometimes strongly correlated leading to a H2/CO ratio around 0.25. This ratio is lower than the ratio from traffic emissions, thus highlighting the mixing of sources in this area.