WP1: Better stratospheric observations through new AirCore technology
- The use of novel AirCore (developed by NOAA, see Karion et al. (2010)) technology provides a cost-effective method to collect vertical profiles of trace gases up to 30 km.
- 45 flights over 9 field campaigns will provide an unprecedented opportunity to investigate stratospheric trace gases on a regular basis over two years.
- Currently only a handful of atmospherically important gases such as carbon dioxide and methane (Karion et al., 2010) have been measured using AirCores, this project will increase that number to more than 30. UEA has the only analytical instrument in Europe (and one of only two world-wide) that has the capability to provide measurements of all important ozone-depleting substances from the very small amounts of air available from AirCores.
WP2: Using improved age of air spectra to diagnose stratospheric circulation changes
- Changes in stratospheric circulation (the Brewer-Dobson Circulation, or BDC) have been mostly investigated via temperature and wind data sets which come with significant limitations and uncertainties.
- An alternative tool is the mean age of air (Hall & Plumb, 1994), defined as the average transit time that an air parcel has spent in the stratosphere.
- Models predict that the mean age is expected to decrease due to a speeding-up of the BDC, but observational studies using trace gases to reconstruct historical mean ages show no detectable acceleration between 1975 and 2010 (e.g. Engel et al., 2009), or that different branches of the BDC may be changing in different ways (e.g. Bönisch et al., 2011).
- WP2 will generate a unique dataset through high precision analysis of over 200 historical stratospheric air samples collected between 1975 and 2012 and will use these data to investigate stratospheric changes over ~40 years.
- Over 50 trace gases will be analysed in these air samples, including all key ozone depleting substances and many important greenhouse gases.
WP3: Using Fractional Release Factors to diagnose stratospheric chemistry changes
- The degree of decomposition of an individual halocarbon gas in a stratospheric air parcel can be quantified as a Fractional Release Factor (FRF). FRFs are relative quantities between 0 (no break-down) and 1 (full break-down) and are assumed to be almost constant with mean age over time.
- FRFs are an important parameter in ozone recovery predictions: to fully diagnose the transport and transformations of trace gases in the stratosphere requires an examination of gases with different breakdown rates and/or sink locations within the stratosphere.
- Currently, small/no uncertainties are assigned to FRFs in ozone recovery predictions (Velders & Daniel, 2014) and they are believed to be constant over time. Data from the air archive analysis (WP2) will allow a detailed investigation of FRFs over time to better constrain our understanding of them, and of future ozone recovery.
WP4: Model comparisons and assessment of future stratospheric and climate impacts
- This project will use existing methodologies (e.g. Newman et al., 2006) in combination with a more detailed understanding of age spectra and FRFs (arising from WP2 and WP3) to calculate improved FRFs and ozone depletion potentials since 1975.
- These will then be compared with similar quantities as extracted/calculated from recent runs of chemistry-climate models, which were carried out for the current Chemistry-Climate Model Initiative (CCMI) and for SPARC (2013).
- A quantification of differences between observations and available UKCA model runs in different stratospheric regions will be the initial result. Implications for the wider suite of CCMI models will also be evaluated.
- The project team will also utilise different emission scenarios from the recent Ozone Assessment (WMO, 2014) and a range of likely future age spectra and FRF scenarios to calculate improved future ozone recovery scenarios up until the year 2100.
References: Bönisch et al., Atmos Chem Phys, 11, 3937–3948, 2011; Engel et al., Nat Geosci, 2, 28–31, 2009; Hall & Plumb, JGR, doi:10.1029/93JD03192, Karion et al., J Atmos Ocean Technol, 27(11), 1839–1853, 2010; Newman et al., Geophys Res Lett, 33, L12814, 2006; SPARC, 2013: Lifetime Assessment, WCRP, 2013; Velders & Daniel, Atmos Chem Phys, 14, 2757-2776, 2014; WMO, 2014: Scientific Assessment of Ozone Depletion, 2014.