7 research outputs found
Investigating stratospheric changes between 2009 and 2018 with halogenated trace gas data from aircraft, AirCores, and a global model focusing on CFC-11
Get PDFWe present new observations of trace gases in the stratosphere based on a cost-effective sampling technique that can access much higher altitudes than aircraft. The further development of this method now provides detection of species with abundances in the parts per trillion (ppt) range and below. We obtain mixing ratios for six gases (CFC-11, CFC-12, HCFC-22, H-1211, H-1301, and SF6), all of which are important for understanding stratospheric ozone depletion and circulation. After demonstrating the quality of the data through comparisons with ground-based records and aircraft-based observations, we combine them with the latter to demonstrate its potential. We first compare the data with results from a global model driven by three widely used meteorological reanalyses. Secondly, we focus on CFC-11 as recent evidence has indicated renewed atmospheric emissions of that species relevant on a global scale. Because the stratosphere represents the main sink region for CFC-11, potential changes in stratospheric circulation and troposphere–stratosphere exchange fluxes have been identified as the largest source of uncertainty for the accurate quantification of such emissions. Our observations span over a decade (up until 2018) and therefore cover the period of the slowdown of CFC-11 global mixing ratio decreases measured at the Earth's surface. The spatial and temporal coverage of the observations is insufficient for a global quantitative analysis, but we do find some trends that are in contrast with expectations, indicating that the stratosphere may have contributed to the slower concentration decline in recent years. Further investigating the reanalysis-driven model data, we find that the dynamical changes in the stratosphere required to explain the apparent change in tropospheric CFC-11 emissions after 2013 are possible but with a very high uncertainty range. This is partly caused by the high variability of mass flux from the stratosphere to the troposphere, especially at timescales of a few years, and partly by large differences between runs driven by different reanalysis products, none of which agree with our observations well enough for such a quantitative analysis
New Fractional Release Factors, Ozone Depletion Potentials, and Lifetimes for Four Long-Lived CFCs: CFC-13, CFC-114, CFC-114a, and CFC-115
No full textKnowing the stratospheric lifetime of an Ozone Depleting Substance (ODS), and its potential depletion of ozone during that time, is vital to reliably monitor and control the use of ODSs. Here, we present improved policy-relevant parameters: Fractional Release Factors (FRFs), Ozone Depletion Potentials (ODPs), and stratospheric lifetimes, for four understudied long-lived CFCs: CFC-13 (CClF3), CFC-114 (CClF2CCCLF2), CFC-114a (CCl2FCF3), and CFC-115 (C2ClF5). Previously derived lifetime estimates for CFC-114 and CFC-115 have substantial uncertainties, while lifetime uncertainties for CFC-13 and CFC-114a are absent from the peer-reviewed literature (Carpenter & Danie et al, 2018).This study used both observational and model data to investigate these compounds and this work derives, for the first time, observation-based lifetimes utilising measurements of air samples collected in the stratosphere. We also used a version of the NASA Goddard Space Flight Center (GSFC) 2-D atmospheric model driven by temperature and transport fields derived from MERRA/MERRA-2 reanalysis.FRFs for these compounds, which had been lacking until now, were derived using stratospheric air samples collected from several research flights with the high-altitude aircraft M55-Geophysica, and the background trend from archived surface air samples from Cape Grim, Tasmania. By using a previously-published correlation between lifetime and FRF for seven well-characterised compounds (CF4, C2F6, C3F8, CHF3, HFC-125, HFC-227ea and SF6), we were able to derive lifetimes for these four new species. Lifetime estimates for CFC-114a agreed within the uncertainties (agreement to one sigma) with the lifetime estimates compiled in Burkholder et al. (2018), while the one for CFC-114 agreed within 2 sigma (measurement-related uncertainties) with those cited in Burkholder et al. (2018). However, observation-based lifetimes for CFC-13 and CFC-115 only agreed with those in Burkholder et al. (2018) within 3 sigma. The lifetime uncertainties in this study were reduced compared to those in Carpenter & Danie et al (2018).As our lifetime estimates for these latter two compounds are notably lower than previous estimates, this suggests that these two compounds may have had greater emissions than previously thought, in order to account for their abundance. It also implies that they will be removed from the atmosphere more quickly than previously thought.New ODPs were derived for these compounds from their new lifetimes and FRFs. Since for two of these compounds (CFC-13 and CFC-114a), there is an absence of observation-derived ODPs in the peer-reviewed literature, this is new and relevant information. The ODPs for CFC-114 and CFC-115 are comparable with estimates from the most recent Scientific Assessment of Ozone Depletion (Burkholder et al., 2018). Providing new and updated lifetimes, FRFs and ODPs for these compounds will help improve future estimates of their tropospheric emissions and their resulting damage to the stratospheric ozone layer.             ReferencesBurkholder et al. (2018). Appendix A, Table A-1 in Scientific Assessment of Ozone Depletion: 2018, Global Ozone Research and Monitoring Project, Report No. 58, World Meteorological Organization, Geneva, Switzerland,  http://ozone.unep.org/science/assessment/sap.Carpenter, L.J., Danie, J.S. et al (2018). Scenarios and Information for Policymakers Chapter 6, Table 6-1 in Scientific Assessment of Ozone Depletion: 2018, Global Ozone Research and Monitoring Project, Report No. 58, World Meteorological Organization, Geneva, Switzerland.</p
Investigating stratospheric circulation and chemistry changes over three decades with trace gas data from aircraft, large balloons, and AirCores
No full textLaube et al. (2020) investigated stratospheric changes between 2009 and 2018 with halogenated trace gas data (CFC-11, CFC-12, H-1211, H-1301, HCFC-22, and SF6) from air samples collected via aircraft and AirCores, and compared the mixing ratios and average stratospheric transit times derived from these observations with those from a global model. We here expand this analysis in three ways: firstly, by adding data from further traces gases such as CFC-115, C2F6, and HCFC-142b to broaden the range of tropospheric trends and stratospheric lifetimes, both of which help to assess the robustness of inferred long-term trends in the stratosphere; secondly, by increasing the temporal span of the observations to nearly three decades using new AirCore observations as well as reanalysed archived air samples collected on board high altitude aircraft and large balloons in the 1990s and 2000s; and thirdly, by investigating the fractional release factors and mean ages of air derived from the aforementioned species as measures of their stratospheric chemistry and the strength of the Brewer-Dobson circulation. In combination with model data from the Chemical Langrangian Model of the Stratosphere (CLaMS) this unique data set allows for an unprecedented evaluation of stratospheric chemistry and dynamics in the mid-latitudes of the Northern Hemisphere
Investigating stratospheric circulation and chemistry changes over three decades with trace gas data from aircraft, large balloons, and AirCores
Get PDFLaube et al. (2020) investigated stratospheric changes between 2009 and 2018 with halogenated trace gas data (CFC-11, CFC-12, H-1211, H-1301, HCFC-22, and SF6) from air samples collected via aircraft and AirCores, and compared the mixing ratios and average stratospheric transit times derived from these observations with those from a global model. We here expand this analysis in three ways: firstly, by adding data from further traces gases such as CFC-115, C2F6, and HCFC-142b to broaden the range of tropospheric trends and stratospheric lifetimes, both of which help to assess the robustness of inferred long-term trends in the stratosphere; secondly, by increasing the temporal span of the observations to nearly three decades using new AirCore observations as well as reanalysed archived air samples collected on board high altitude aircraft and large balloons in the 1990s and 2000s; and thirdly, by investigating the fractional release factors and mean ages of air derived from the aforementioned species as measures of their stratospheric chemistry and the strength of the Brewer-Dobson circulation. In combination with model data from the Chemical Langrangian Model of the Stratosphere (CLaMS) this unique data set allows for an unprecedented evaluation of stratospheric chemistry and dynamics in the mid-latitudes of the Northern Hemisphere. ReferencesLaube, et al., Atmos. Chem. Phys., 20, 9771–9782, 2020, https://doi.org/10.5194/acp-20-9771-2020</p
Investigating stratospheric circulation and chemistry changes over three decades with trace gas data from aircraft, large balloons, and AirCores
No full textLaube et al. (2020) investigated stratospheric changes between 2009 and 2018 with halogenated trace gas data (CFC-11, CFC-12, H-1211, H-1301, HCFC-22, and SF6) from air samples collected via aircraft and AirCores, and compared the mixing ratios and average stratospheric transit times derived from these observations with those from a global model. We here expand this analysis in three ways: firstly, by adding data from further traces gases such as CFC-115, C2F6, and HCFC-142b to broaden the range of tropospheric trends and stratospheric lifetimes, both of which help to assess the robustness of inferred long-term trends in the stratosphere; secondly, by increasing the temporal span of the observations to nearly three decades using new AirCore observations as well as reanalysed archived air samples collected on board high altitude aircraft and large balloons in the 1990s and 2000s; and thirdly, by investigating the fractional release factors and mean ages of air derived from the aforementioned species as measures of their stratospheric chemistry and the strength of the Brewer-Dobson circulation. In combination with model data from the Chemical Langrangian Model of the Stratosphere (CLaMS) this unique data set allows for an unprecedented evaluation of stratospheric chemistry and dynamics in the mid-latitudes of the Northern Hemisphere. ReferencesLaube, et al., Atmos. Chem. Phys., 20, 9771–9782, 2020, https://doi.org/10.5194/acp-20-9771-2020</p
