Comparison of continuous in situ CO2 observations at Jungfraujoch using two different measurement techniques

Since 2004, atmospheric carbon dioxide (CO2) is being measured at the High Altitude Research Station Jungfraujoch by the division of Climate and Environmental Physics at the University of Bern (KUP) using a nondispersive infrared gas analyzer (NDIR) in combination with a paramagnetic O2 analyzer. In January 2010, CO2 measurements based on cavity ring-down spectroscopy (CRDS) as part of the Swiss National Air Pollution Monitoring Network were added by the Swiss Federal Laboratories for Materials Science and Technology (Empa). To ensure a smooth transition – a prerequisite when merging two data sets, e.g., for trend determinations – the two measurement systems run in parallel for several years. Such a long-term intercomparison also allows the identification of potential offsets between the two data sets and the collection of information about the compatibility of the two systems on different time scales. A good agreement of the seasonality, short-term variations and, to a lesser extent mainly due to the short common period, trend calculations is observed. However, the comparison reveals some issues related to the stability of the calibration gases of the KUP system and their assigned CO2 mole fraction. It is possible to adapt an improved calibration strategy based on standard gas determinations, which leads to better agreement between the two data sets. By excluding periods with technical problems and bad calibration gas cylinders, the average hourly difference (CRDS – NDIR) of the two systems is −0.03 ppm ± 0.25 ppm. Although the difference of the two data sets is in line with the compatibility goal of ±0.1 ppm of the World Meteorological Organization (WMO), the standard deviation is still too high. A significant part of this uncertainty originates from the necessity to switch the KUP system frequently (every 12 min) for 6 min from ambient air to a working gas in order to correct short-term variations of the O2 measurement system. Allowing additional time for signal stabilization after switching the sample, an effective data coverage of only one-sixth for the KUP system is achieved while the Empa system has a nearly complete data coverage. Additionally, different internal volumes and flow rates may affect observed differences

Volatile Organic Compounds in the Po Basin. Part A: Anthropogenic VOCs

Measurements of volatile organic compounds (VOCs) were performed in the Po Basin, northern Italy in early summer 1998 within the PIPAPO project as well as in summer 2002 and autumn 2003 within the FORMAT project. During the three campaigns, trace gases and meteorological parameters were measured at a semi-rural station, around 35 km north of the city center of Milan. Low toluene and benzene concentrations and lower toluene to benzene ratios on weekends, on Sundays, and in August enabled the identification of a ‘weekend' and a ‘vacation' effect when anthropogenic emissions were lower due to less traffic and reduced industrial activities, respectively. Recurrent nighttime cyclohexane peaks suggested a periodical short-term release of cyclohexane close to the semi-rural sampling site. A multivariate receptor model analysis resulted in the distinction of different characteristic concentration profiles attributed to natural gas, biogenic impact, vehicle exhaust, industrial activities, and a single cyclohexane sourc

Mechanical support concept of the DEMO breeding blanket

The DEMO tokamak architecture is based on large vertical breeding blanket (BB) segments that are accessed from a maintenance hall above the tokamak and are vertically replaced through large upper ports of the vacuum vessel (VV). The feasibility of the BB segments mechanical supports is a prerequisite of this vertical segment architecture. Their design directly impacts on the removal kinematics and the remote handling operations required for release and engagement. The supports must withstand large forces acting on the BB in particular due to electromagnetic (EM) loads. At the same time, they must ensure a sufficiently precise positioning of the BB first wall. Their design also takes into account the significant thermal expansion of the blanket segments that are operated at high temperature avoiding excessive support reaction forces. The BB support concept described in this article does not require fasteners or electrical straps to the VV and therefore much reduces the complexity of the BB remote replacement – a valuable characteristic that would make this concept a milestone in meeting one of the goals defined for the DEMO project: to develop a maintainable fusion power plant design [1]. Each blanket segment is individually supported by the VV without any physical contact to the other blankets or in-vessel components. It relies instead on vertical pre-compression inside the VV due to obstructed thermal expansion and radial pre-compression due to the ferromagnetic force acting on the BB material in the toroidal magnetic field. The verification process did not identify show stoppers. Nonetheless, a further evolution of the concept is required including design improvements to mitigate the high stress levels found in the inboard blankets during plasma disruptions. The fact that no excessively high support reaction forces or large BB deflections were found suggests though that the further development of the concept could be successful

Using radon-222 to distinguish between vertical transport processes at Jungfraujoch

Trace gases measured at Jungfrajoch, a key baseline monitoring station in the Swiss Alps, are tranported from the surface to the alpine ridge by several different processes. On clear days with weak synoptic forcing, thermally-driven upslope mountain winds (anabatic winds) are prevalent. Using hourly radon–222 observations, which are often used to identify air of terrestrial origin, we used the shape of the diurnal cycle to sort days according to the strength of anabatic winds. Radon is ideal as an airmass tracer because it is emitted from soil at a relatively constant rate, it is chemically inert, and decays with a half-life of 3.8 days. Because of its short half-life, radon concentrations are much lower in the free troposphere than in boundary-layer air over land. For comparable radon concentrations, anabatic wind days at Jungfraujoch are different from non-anabatic days in terms of the average wind speed, humidity, air temperature anomalies, and trace species. As a consequence, future studies could be devised which focus on a subset of days, e.g. by excluding anabatic days, with the intention of choosing a set of days which can be more accurately simulated by a transport model. © Author(s) 2014

Volatile Organic Compounds in the Po Basin. Part B: Biogenic VOCs

Measurements of volatile organic compounds (VOCs) were performed in the Po Basin, northern Italy in early summer 1998, summer 2002, and autumn 2003. During the three campaigns, trace gases and meteorological parameters were measured at a semi-rural station, around 35 km north of the city center of Milan. Bimodal diurnal cycles of isoprene with highest concentrations in the morning and evening were found and could be explained by the interaction of emissions, chemical reactions, and vertical mixing. The diurnal cycle could be qualitatively reproduced by a three-dimensional Eulerian model. The nighttime decay of isoprene could be attributed mostly to reactions with NO3, while the decay of the isoprene oxidation products could not be explained with the considered chemical reactions. Methanol reached very high mixing ratios, up to 150 ppb. High concentrations with considerable variability occurred during nights with high relative humidities and low wind speeds. The origin of these nighttime methanol concentrations is most likely local and biogenic but the specific source could not be identifie

TransCom N2O model inter-comparison - Part 2:Atmospheric inversion estimates of N2O emissions

This study examines N2O emission estimates from five different atmospheric inversion frameworks based on chemistry transport models (CTMs). The five frameworks differ in the choice of CTM, meteorological data, prior uncertainties and inversion method but use the same prior emissions and observation data set. The posterior modelled atmospheric N2O mole fractions are compared to observations to assess the performance of the inversions and to help diagnose problems in the modelled transport. Additionally, the mean emissions for 2006 to 2008 are compared in terms of the spatial distribution and seasonality. Overall, there is a good agreement among the inversions for the mean global total emission, which ranges from 16.1 to 18.7 TgN yr(-1) and is consistent with previous estimates. Ocean emissions represent between 31 and 38% of the global total compared to widely varying previous estimates of 24 to 38%. Emissions from the northern mid- to high latitudes are likely to be more important, with a consistent shift in emissions from the tropics and subtropics to the mid- to high latitudes in the Northern Hemisphere; the emission ratio for 0-30A degrees N to 30-90A degrees N ranges from 1.5 to 1.9 compared with 2.9 to 3.0 in previous estimates. The largest discrepancies across inversions are seen for the regions of South and East Asia and for tropical and South America owing to the poor observational constraint for these areas and to considerable differences in the modelled transport, especially inter-hemispheric exchange rates and tropical convective mixing. Estimates of the seasonal cycle in N2O emissions are also sensitive to errors in modelled stratosphere-to-troposphere transport in the tropics and southern extratropics. Overall, the results show a convergence in the global and regional emissions compared to previous independent studies

INVESTIGATING THE USE OF COASTAL BLUE IMAGERY FOR BATHYMETRIC MAPPING OF INLAND WATER BODIES

In this contribution, we report on an experimental airborne data acquisition with two medium format cameras (Coastal Blue, RGB) and a topo-bathymetric laser scanner for capturing the bathymetry of a dozen of groundwater supplied lakes located near Augsburg, Germany. The specific research question was to investigate whether the use of high-resolution Coastal Blue imagery (λ = 400–460 nm) provides added value for mapping bathymetry and characterization of water bottom features. While data processing is still in progress, preliminary results indicate that the blue (λ = 420–500 nm) and green (λ = 490–570 nm) color channels of the RGB camera are better suited for estimating bathymetry, but the Coastal Blue channel adds an additional water penetrating band increasing the number of useful band combinations with a positive effect on the water bottom classification capabilities. Whereas Coastal Blue channels are rather used from satellite platforms (Landsat 8, WorldView-2) with spatial resolutions in the meter range, our experiment aims at using higher resolution Coastal Blue imagery with a ground sampling distance of around 5 cm enabling not only spectrally based shallow water depth mapping but also the application of multi-media photogrammetry in high spatial resolution. To the best of our knowledge the use of high-resolution Coastal Blue captured from airborne platforms is novel in the context of mapping shallow water bathymetry

A new estimation of the recent tropospheric molecular hydrogen budget using atmospheric observations and variational inversion

This paper presents an analysis of the recent tropospheric molecular hydrogen (H2) budget with a particular focus on soil uptake and European surface emissions. A variational inversion scheme is combined with observations from the RAMCES and EUROHYDROS atmospheric networks, which include continuous measurements performed between mid-2006 and mid-2009. Net H2 surface flux, then deposition velocity and surface emissions and finally, deposition velocity, biomass burning, anthropogenic and N2 fixation-related emissions were simultaneously inverted in several scenarios. These scenarios have focused on the sensibility of the soil uptake value to different spatio-temporal distributions. The range of variations of these diverse inversion sets generate an estimate of the uncertainty for each term of the H2 budget. The net H2 flux per region (High Northern Hemisphere, Tropics and High Southern Hemisphere) varies between −8 and +8 Tg yr−1. The best inversion in terms of fit to the observations combines updated prior surface emissions and a soil deposition velocity map that is based on bottom-up and top-down estimations. Our estimate of global H2 soil uptake is −59±9 Tg yr−1. Forty per cent of this uptake is located in the High Northern Hemisphere and 55% is located in the Tropics. In terms of surface emissions, seasonality is mainly driven by biomass burning emissions. The inferred European anthropogenic emissions are consistent with independent H2 emissions estimated using a H2/CO mass ratio of 0.034 and CO emissions within the range of their respective uncertainties. Additional constraints, such as isotopic measurements would be needed to infer a more robust partition of H2 sources and sinks