References of "Kinnison, D E"
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See detailQuantification of Stratospheric Ozone Recovery Due to Anthropogenic Halogens
Salawitch, R. J.; Tribett, W.; Wales, P. et al

Conference (2020, January 14)

Human release of CFCs and other ozone depleting substances (ODS) has led to a slow, steady erosion of the thickness of the global ozone layer over the past several decades. The ozone layer has begun to ... [more ▼]

Human release of CFCs and other ozone depleting substances (ODS) has led to a slow, steady erosion of the thickness of the global ozone layer over the past several decades. The ozone layer has begun to recover due to actions taken under the Montreal Protocol, which has led to a decrease in the atmospheric abundance of ozone depleting substances. Yet, unreported emissions of CFC-11 have led to a slower than expected decline, and there has been a rise in the atmospheric abundance of chlorinated very short lived (VSL) compounds not regulated under the Montreal Protocol. In this presentation, we examine time series of ozone and halogens from a variety of observational platforms to quantify the attribution of the change in stratospheric ozone that is due to halogens. Our focus is on the extra-polar region: i.e., the state of the ozone layer between 55S and 55N where the vast majority of the world’s population resides. We will quantify the effect of continued release of CFC-11 and the presence of chlorinated VSL species on the recovery of the ozone layer. Additionally, we will use atmospheric observations to evaluate several proposed formulations for defining the quantity known as “Equivalent Effective Stratospheric Chlorine” (EESC) and assess the impact of these formulations on the projected recovery of the ozone layer. [less ▲]

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See detailAnalysis of trends in total stratospheric ozone
Salawitch, Ross J; Tribett, W R; Wales, P et al

Conference (2018, December 12)

Time series of total column ozone have exhibited unusual, unexpected behavior over the past few years. In year 2016, total ozone was lower than expected based on some forecasts that utilize the time ... [more ▼]

Time series of total column ozone have exhibited unusual, unexpected behavior over the past few years. In year 2016, total ozone was lower than expected based on some forecasts that utilize the time evolution of equivalent effective stratosphere chlorine (EESC). Conversely, total column ozone exhibited a sharp rise in 2017. The existence of a new formulation (i.e., Engel et al., ACP, 2017) for the fractional release factors (FRFs) used to find EESC for mid-latitude lower stratospheric air parcels, the contribution of very short-lived chlorine and bromine compounds to EESC, as well as possible temporal variations in tropospheric column ozone compound the difficulty in establishing a quantitative relationship between the time evolution of EESC and stratospheric ozone. This presentation will consist of an analysis of the ~40 year record of total column ozone measured from space (e.g., version 8.6 of the NASA SBUV Merged Ozone Data Set at the time of abstract submission), along with: a) stratospheric chlorine loading from various satellite instruments as well as the long-term ground-based measurement from Jungfraujoch, Switzerland; b) various other quantities that affect the long-term evolution of stratospheric ozone (e.g., total solar irradiance, stratospheric optical depth, quasi-biennial oscillation of the direction of tropical stratospheric winds) c) estimates of tropospheric column ozone to assess our understanding of trends in total stratospheric ozone. Preliminary results indicate better quantitative understanding is attained for the new FRFs, which lead to a more gradual recovery of total stratospheric ozone than is found using the old FRFs. Reference: Engel, A. et al., ACP, 18, 601619, doi:10.5194/acp-18-601-2018, 2018. [less ▲]

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See detailSPARC Report on the Mystery of Carbon Tetrachloride
Ahmadzai, H; Bock, R P; Burkholder, J B et al

in Liang, Qing; Newman, Paul A; Reimann, Stefan (Eds.) SPARC Report on the Mystery of Carbon Tetrachloride (2016)

The Montreal Protocol (MP) controls the production and consumption of carbon tetrachloride (CCl4 or CTC) and other ozone-depleting substances (ODSs) for emissive uses. CCl4 is a major ODS, accounting for ... [more ▼]

The Montreal Protocol (MP) controls the production and consumption of carbon tetrachloride (CCl4 or CTC) and other ozone-depleting substances (ODSs) for emissive uses. CCl4 is a major ODS, accounting for about 12% of the globally averaged inorganic chlorine and bromine in the stratosphere, compared to 14% for CFC-12 in 2012. In spite of the MP controls, there are large ongoing emissions of CCl4 into the atmosphere. Estimates of emissions from various techniques ought to yield similar numbers. However, the recent WMO/UNEP Scientific Assessment of Ozone Depletion [WMO, 2014] estimated a 2007-2012 CCl4 bottom-up emission of 1-4 Gg/year (1-4 kilotonnes/year), based on country-by-country reports to UNEP, and a global top-down emissions estimate of 57 Gg/ year, based on atmospheric measurements. This 54 Gg/year difference has not been explained. In order to assess the current knowledge on global CCl4 sources and sinks, stakeholders from industrial, governmental, and the scientific communities came together at the “Solving the Mystery of Carbon Tetrachloride” workshop, which was held from 4-6 October 2015 at Empa in Dübendorf, Switzerland. During this workshop, several new findings were brought forward by the participants on CCl4 emissions and related science. • Anthropogenic production and consumption for feedstock and process agent uses (e.g., as approved solvents) are reported to UNEP under the MP. Based on these numbers, global bottom-up emissions of 3 (0-8) Gg/year are estimated for 2007-2013 in this report. This number is also reasonably consistent with this report’s new industry-based bottom-up estimate for fugitive emissions of 2 Gg/year. • By-product emissions from chloromethanes and perchloroethylene plants are newly proposed in this report as significant CCl4 sources, with global emissions estimated from these plants to be 13 Gg/year in 2014. • This report updates the anthropogenic CCl4 emissions estimation as a maximum of ~25 Gg/year. This number is derived by combining the above fugitive and by-product emissions (2 Gg/year and 13 Gg/year, respectively) with 10 Gg/year from legacy emissions plus potential unreported inadvertent emissions from other sources. • Ongoing atmospheric CCl4 measurements within global networks have been exploited for assessing regional emissions. In addition to existing emissions estimates from China and Australia, the workshop prompted research on emissions in the U.S. and Europe. The sum of these four regional emissions is estimated as 21±7.5a Gg/year, but this is not a complete global accounting. These regional top-down emissions estimates also show that most of the CCl4 emissions originate from chemical industrial regions, and are not linked to major population centres. • The total CCl4 lifetime is critical for calculating top-down global emissions. CCl4 is destroyed in the stratosphere, oceans, and soils, complicating the total lifetime estimate. The atmospheric lifetime with respect to stratospheric loss was recently revised to 44 (36-58) years, and remains unchanged in this report. New findings from additional measurement campaigns and reanalysis of physical parameters lead to changes in the ocean lifetime from 94 years to 210 (157-313) years, and in the soil lifetime from 195 years to 375 (288-536) years. • These revised lifetimes lead to an increase of the total lifetime from 26 years in WMO [2014] to 33 (28-41) years. Consequently, CCl4 is lost at a slower rate from the atmosphere. With this new total lifetime, the global top-down emissions calculation decreases from 57 (40-74) Gg/year in WMO [2014] to 40 (25-55) Gg/year. This estimate is relatively consistent with the independent gradient top-down emissions of 30 (25-35) Gg/year, based upon differences between atmospheric measurements of CCl4 in the Northern and Southern Hemispheres. In addition, this new total lifetime implies an upper limit of 3-4 Gg/year of natural emissions, based upon newly reported observations of old air in firn snow. These new CCl4 emissions estimates from the workshop make considerable progress toward closing the emissions discrepancy. The new industrial bottom-up emissions estimate (15 Gg/year total) includes emissions from chloromethanes plants (13 Gg/year) and feedstock fugitive emissions (2 Gg/year). When combined with legacy emissions and unreported inadvertent emissions, this could be up to 25 Gg/year. Top-down emissions estimates are: global 40 (25-55) Gg/year, gradient 30 (25-35) Gg/year, and regional 21 (14-28) Gg/year. While the new bottom-up value is still less than the aggregated top-down values, these estimates reconcile the CCl4 budget discrepancy when considered at the edges of their uncertainties. [less ▲]

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