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Emissions of sulphur hexafluoride (SF6), one of the strongest greenhouse gases on a per molecule basis, are targeted to be collectively reduced under the Kyoto Protocol. Because of its long atmospheric lifetime (estimated as 800 to 3200 years), the accumulation of SF6 in the atmosphere is a direct measure of its global emissions. Examination of our extended data set of globally distributed high-precision SF6 observations shows an increase in SF6 abundance from near zero in the 1970s to a global mean of 6.7 ppt by the end of 2008. In-depth evaluation of our long-term data records shows that the global source of SF6 decreased after 1995, most likely due to SF6 emission reductions in industrialised countries, but increased again after 1998. By subtracting those emissions reported by Annex I countries to the United Nations Framework Convention of Climatic Change (UNFCCC) from our observation-inferred SF6 source leaves a surprisingly large gap of more than 70–80% of non-reported SF6 emissions in the last decade. This suggests a strong under-estimation of emissions in Annex I countries and underlines the urgent need for independent atmospheric verification of greenhouse gases emissions accounting.
We report the first measurements of 1,1,1,2,3,3,3-heptafluoropropane (HFC-227ea), a substitute for ozone depleting compounds, in remote regions of the atmosphere and present evidence for its rapid growth. Observed mixing ratios ranged from below 0.01 ppt in deep firn air to 0.59 ppt in the northern mid-latitudinal upper troposphere. Firn air samples collected in Greenland were used to reconstruct a history of atmospheric abundance. Year-on-year increases were deduced, with acceleration in the growth rate from 0.026 ppt per year in 2000 to 0.057 ppt per year in 2007. Upper tropospheric air samples provide evidence for a continuing growth until late 2009. Fur- thermore we calculated a stratospheric lifetime of 370 years from measurements of air samples collected on board high altitude aircraft and balloons. Emission estimates were determined from the reconstructed atmospheric trend and suggest that current "bottom-up" estimates of global emissions for 2005 are too high by more than a factor of three.
In this paper we present evidence that the observed increase in tropical upwelling after the year 2000 may be attributed to a change in the Brewer-Dobson circulation pattern. For this purpose, we use the concept of transit times derived from residual circulation trajectories and different in-situ measurements of ozone and nitrous dioxide. Observations from the Canadian midlatitude ozone profile record, probability density functions of in-situ N2O observations and a shift of the N2O-O3 correlation slopes, taken together, indicate that the increased upwelling in the tropics after the year 2000 appears to have triggered an intensification of tracer transport from the tropics into the extratropics in the lower stratosphere below about 500 K. This finding is corroborated by the fact that transit times along the shallow branch of the residual circulation into the LMS have decreased for the same time period (1993–2003). On a longer time scale (1979–2009), the transit time of the shallow residual circulation branch show a steady decrease of about −1 month/decade over the last 30 years, while the transit times of the deep branch remain unchanged. This highlights the fact that a change in the upwelling across the tropical tropopause is not a direct indicator for changes of the whole Brewer-Dobson circulation.
Fractional release factors of long-lived halogenated organic compounds in the tropical stratosphere
(2010)
Fractional release factors (FRFs) of organic trace gases are time-independent quantities that influence the calculation of Global Warming Potentials and Ozone Depletion Potentials. We present the first set of vertically resolved FRFs for 15 long-lived halocarbons in the tropical stratosphere up to 34 km altitude. They were calculated from measurements on air samples collected on board balloons and a high altitude aircraft. We compare the derived dependencies of FRFs on the mean stratospheric transit times (the so-called mean ages of air) with similarly derived FRFs originating from measurements at higher latitudes and find significant differences. Moreover a comparison with averaged FRFs currently used by the World Meteorological Organisation revealed the limitations of these measures due to their observed vertical and latitudinal variability. The presented data set could be used to improve future ozone level and climate projections.
Active chlorine species play a dominant role in the catalytic destruction of stratospheric ozone in the polar vortices during the late winter and early spring seasons. Recently, the correct understanding of the ClO dimer cycle was challenged by the release of new laboratory absorption cross sections (Pope et al., 2007) yielding significant model underestimates of observed ClO and ozone loss (von Hobe et al., 2007). Under this aspect, nocturnal Arctic stratospheric limb emission measurements carried out by the balloon version of the Michelson Interferometer for Passive Atmospheric Sounding (MIPAS-B) from Kiruna (Sweden) on 11 January 2001 and 20/21 March 2003 have been reanalyzed with regard to the chlorine reservoir species ClONO2 and the active species, ClO and ClOOCl (Cl2O2). New laboratory measurements of IR absorption cross sections of ClOOCl for various temperatures and pressures allowed for the first time the retrieval of ClOOCl mixing ratios from remote sensing measurements. High values of active chlorine (ClOx) of roughly 2.3 ppbv at 20 km were observed by MIPAS-B in the cold mid-winter Arctic vortex on 11 January 2001. While nighttime ClOOCl shows enhanced values of nearly 1.1 ppbv at 20 km, ClONO2 mixing ratios are less than 0.1 ppbv at this altitude. In contrast, high ClONO2 mixing ratios of nearly 2.4 ppbv at 20 km have been observed in the late winter Arctic vortex on 20 March 2003. No significant ClOx amounts are detectable on this date since most of the active chlorine has already recovered to its main reservoir species ClONO2. The observed values of ClOx and ClONO2 are in line with the established polar chlorine chemistry. The thermal equilibrium constants between the dimer formation and its dissociation, as derived from the balloon measurements, are on the lower side of reported data and in good agreement with values recommended by von Hobe et al. (2007). Calculations with the ECHAM/MESSy Atmospheric Chemistry model (EMAC) using established kinetics show similar chlorine activation and deactivation, compared to the measurements in January 2001 and March 2003, respectively.
We report the first measurements of 1,1,1,2,3,3,3-heptafluoropropane (HFC-227ea), a substitute for ozone depleting compounds, in air samples originating from remote regions of the atmosphere and present evidence for its accelerating growth. Observed mixing ratios ranged from below 0.01 ppt in deep firn air to 0.59 ppt in the current northern mid-latitudinal upper troposphere. Firn air samples collected in Greenland were used to reconstruct a history of atmospheric abundance. Year-on-year increases were deduced, with acceleration in the growth rate from 0.029 ppt per year in 2000 to 0.056 ppt per year in 2007. Upper tropospheric air samples provide evidence for a continuing growth until late 2009. Furthermore we calculated a stratospheric lifetime of 370 years from measurements of air samples collected on board high altitude aircraft and balloons. Emission estimates were determined from the reconstructed atmospheric trend and suggest that current "bottom-up" estimates of global emissions for 2005 are too high by a factor of three.
This paper presents an analysis of the recent tropospheric molecular hydrogen (H2) budget with a particular focus on soil uptake and 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, soil uptake distinct from surface emissions and finally, soil uptake, biomass burning, anthropogenic emissions and N2 fixation-related emissions separately were inverted in several scenarios. The various inversions generate an estimate 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 soil uptake measurements. Our estimate of global H2 soil uptake is −59 ± 4.0 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 considering their respective uncertainties. To constrain a more robust partition of H2 sources and sinks would need additional constraints, such as isotopic measurements.