Browsing by Author "Tummon, Fiona"

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    Atmospheric isoprene measurements reveal larger-than-expected Southern Ocean emissions
    (Springer Nature, 2024-03-22) Ferracci, Valerio; Weber, James; Bolas, Conor G.; Robinson, Andrew D.; Tummon, Fiona; Rodríguez-Ros, Pablo; Cortés-Greus, Pau; Baccarini, Andrea; Jones, Roderic L.; Galí, Martí; Simó, Rafel; Schmale, Julia; Harris, Neil
    Isoprene is a key trace component of the atmosphere emitted by vegetation and other organisms. It is highly reactive and can impact atmospheric composition and climate by affecting the greenhouse gases ozone and methane and secondary organic aerosol formation. Marine fluxes are poorly constrained due to the paucity of long-term measurements; this in turn limits our understanding of isoprene cycling in the ocean. Here we present the analysis of isoprene concentrations in the atmosphere measured across the Southern Ocean over 4 months in the summertime. Some of the highest concentrations ( >500 ppt) originated from the marginal ice zone in the Ross and Amundsen seas, indicating the marginal ice zone is a significant source of isoprene at high latitudes. Using the United Kingdom Earth System Model we show that current estimates of sea-to-air isoprene fluxes underestimate observed isoprene by a factor >20. A daytime source of isoprene is required to reconcile models with observations. The model presented here suggests such an increase in isoprene emissions would lead to >8% decrease in the hydroxyl radical in regions of the Southern Ocean, with implications for our understanding of atmospheric oxidation and composition in remote environments, often used as proxies for the pre-industrial atmosphere.
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    Overview of the Antarctic circumnavigation expedition: study of preindustrial-like aerosols and their climate effects (ACE-SPACE)
    (American Meteorological Society, 2019-07-02) Schmale, Julia; Baccarini, Andrea; Thurnherr, Iris; Henning, Silvia; Efraim, Avichay; Regayre, Leighton; Bolas, Conor; Hartmann, Markus; Welti, André; Lehtipalo, Katrianne; Aemisegger, Franziska; Tatzelt, Christian; Landwehr, Sebastian; Modini, Robin l.; Tummon, Fiona; Johnson, Jill S.; Harris, Neil R. P.; Schnaiter, Martin; Toffoli, Alessandro; Derkani, Marzieh; Bukowiecki, Nicolas; Stratmann, Frank; Dommen, Josef; Baltensperger, Urs; Wernli, Heini; Rosenfeld, Daniel; Gysel-Beer, Martin; Carslaw, Ken S.
    Aerosol characteristics over the Southern Ocean are surprisingly heterogeneous because of the distinct regional dynamics and marine microbial regimes. Satellite observations and model simulations underestimate the abundance of cloud condensation nuclei. Uncertainty in radiative forcing caused by aerosol-cloud interactions is about twice as large as for CO2 and remains the least well-understood anthropogenic contribution to climate change. A major cause of uncertainty is the poorly-quantified state of aerosols in the pristine-preindustrial atmosphere, which defines the baseline against which anthropogenic effects are calculated. The Southern Ocean is one of the few remaining near-pristine aerosol environments on Earth, but there are very few measurements to evaluate models. The Antarctic Circumnavigation Expedition: Study of Preindustrial-like Aerosols and their Climate Effects (ACE-SPACE) took place between December 2016 and March 2017 and covered the entire Southern Ocean region (Indian, Pacific and Atlantic Oceans, ship track > 33,000 km) including previously unexplored areas. In situ measurements covered aerosol characteristics (e.g., chemical composition, size distributions, and cloud condensation nuclei (CCN) number concentrations), trace gases and meteorological variables. Remote sensing observations of cloud properties, the physical and microbial ocean state, as well as back trajectory analyses are used to interpret the in situ data. The contribution of sea spray to CCN in the westerly wind belt can be larger than 50%. The abundance of methanesulfonic acid indicates local and regional microbial influence on CCN abundance in Antarctic coastal waters and in the open ocean. We use the in situ data to evaluate simulated CCN concentrations from a global aerosol model. The extensive, available ACE-SPACE dataset (https://zenodo.org/communities/spi-ace?page=1&size=20) provides an unprecedented opportunity to evaluate models and to reduce the uncertainty in radiative forcing associated with the natural processes of aerosol emission, formation, transport and processing occurring over the pristine Southern Ocean.
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    An update on ozone profile trends for the period 2000 to 2016
    (European Geosciences Union (EGU) / Copernicus Publications, 2017-09-11) Steinbrecht, Wolfgang; Froidevaux, Lucien; Fuller, Ryan; Wang, Ray; Anderson, John; Roth, Chris; Bourassa, Adam; Degenstein, Doug; Damadeo, Robert; Zawodny, Joe; Frith, Stacey; McPeters, Richard; Bhartia, Pawan; Wild, Jeannette; Long, Craig; Davis, Sean; Rosenlof, Karen; Sofieva, Viktoria; Walker, Kaley; Rahpoe, Nabiz; Rozanov, Alexei; Weber, Mark; Laeng, Alexandra; von Clarmann, Thomas; Stiller, Gabriele; Kramarova, Natalya; Godin-Beekmann, Sophie; Leblanc, Thierry; Querel, Richard; Swart, Daan; Boyd, Ian; Hocke, Klemens; Kämpfer, Niklaus; Maillard Barras, Eliane; Moreira, Lorena; Nedoluha, Gerald; Vigouroux, Corinne; Blumenstock, Thomas; Schneider, Matthias; García, Omaira; Jones, Nicholas; Mahieu, Emmanuel; Smale, Dan; Kotkamp, Michael; Robinson, John; Petropavlovskikh, Irina; Harris, Neil; Hassler, Birgit; Hubert, Daan; Tummon, Fiona
    Ozone profile trends over the period 2000 to 2016 from several merged satellite ozone data sets and from ground-based data measured by four techniques at stations of the Network for the Detection of Atmospheric Composition Change indicate significant ozone increases in the upper stratosphere, between 35 and 48 km altitude (5 and 1 hPa). Near 2 hPa (42 km), ozone has been increasing by about 1.5 % per decade in the tropics (20° S to 20° N), and by 2 to 2.5 % per decade in the 35 to 60° latitude bands of both hemispheres. At levels below 35 km (5 hPa), 2000 to 2016 ozone trends are smaller and not statistically significant. The observed trend profiles are consistent with expectations from chemistry climate model simulations. This study confirms positive trends of upper stratospheric ozone already reported, e.g., in the WMO/UNEP Ozone Assessment 2014 or by Harris et al. (2015). Compared to those studies, three to four additional years of observations, updated and improved data sets with reduced drift, and the fact that nearly all individual data sets indicate ozone increase in the upper stratosphere, all give enhanced confidence. Uncertainties have been reduced, for example for the trend near 2 hPa in the 35 to 60° latitude bands from about ±5 % (2σ) in Harris et al. (2015) to less than ±2 % (2σ). Nevertheless, a thorough analysis of possible drifts and differences between various data sources is still required, as is a detailed attribution of the observed increases to declining ozone-depleting substances and to stratospheric cooling. Ongoing quality observations from multiple independent platforms are key for verifying that recovery of the ozone layer continues as expected.