Browsing by Author "Palmer, Paul I."

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    Isotopic signatures of methane emissions from tropical fires, agriculture and wetlands: the MOYA and ZWAMPS flights
    (The Royal Society, 2021-12-06) MOYA/ZWAMPS Team; Nisbet, Euan; Allen, Grant; Fisher, Rebecca E.; France, James L.; Lee, James D.; Lowry, David; Andrade, Marcos F.; Bannan, Thomas J.; Barker, Patrick; Bateson, Prudence; Bauguitte, Stéphane J.-B.; Bower, Keith N.; Broderick, Tim J.; Chibesakunda, Francis; Cain, Michelle; Cozens, Alice E.; Daly, Michael C.; Ganesan, Anita L.; Jones, Anna E.; Lambakasa, Musa; Lunt, Mark F.; Mehra, Archit; Moreno, Isabel; Pasternak, Dominika; Palmer, Paul I.; Percival, Carl J.; Pitt, Joseph R.; Riddle, Amber J.; Rigby, Matthew; Shaw, Jacob T.; Stell, Angharad C.; Vaughan, Adam R.; Warwick, Nicola J.; Wilde, Shona E.
    We report methane isotopologue data from aircraft and ground measurements in Africa and South America. Aircraft campaigns sampled strong methane fluxes over tropical papyrus wetlands in the Nile, Congo and Zambezi basins, herbaceous wetlands in Bolivian southern Amazonia, and over fires in African woodland, cropland and savannah grassland. Measured methane δ13CCH4 isotopic signatures were in the range −55 to −49‰ for emissions from equatorial Nile wetlands and agricultural areas, but widely −60 ± 1‰ from Upper Congo and Zambezi wetlands. Very similar δ13CCH4 signatures were measured over the Amazonian wetlands of NE Bolivia (around −59‰) and the overall δ13CCH4 signature from outer tropical wetlands in the southern Upper Congo and Upper Amazon drainage plotted together was −59 ± 2‰. These results were more negative than expected. For African cattle, δ13CCH4 values were around −60 to −50‰. Isotopic ratios in methane emitted by tropical fires depended on the C3 : C4 ratio of the biomass fuel. In smoke from tropical C3 dry forest fires in Senegal, δ13CCH4 values were around −28‰. By contrast, African C4 tropical grass fire δ13CCH4 values were −16 to −12‰. Methane from urban landfills in Zambia and Zimbabwe, which have frequent waste fires, had δ13CCH4 around −37 to −36‰. These new isotopic values help improve isotopic constraints on global methane budget models because atmospheric δ13CCH4 values predicted by global atmospheric models are highly sensitive to the δ13CCH4 isotopic signatures applied to tropical wetland emissions. Field and aircraft campaigns also observed widespread regional smoke pollution over Africa, in both the wet and dry seasons, and large urban pollution plumes. The work highlights the need to understand tropical greenhouse gas emissions in order to meet the goals of the UNFCCC Paris Agreement, and to help reduce air pollution over wide regions of Africa. This article is part of a discussion meeting issue 'Rising methane: is warming feeding warming? (part 2)'.
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    Mapping water levels across a region of the Cuvette Centrale peatland complex
    (MDPI, 2023-06-13) Georgiou, Selena; Mitchard, Edward T. A.; Crezee, Bart; Dargie, Greta C.; Young, Dylan M.; Jovani-Sancho, Antonio J.; Kitambo, Benjamin; Papa, Fabrice; Bocko, Yannick E.; Bola, Pierre; Crabtree, Dafydd E.; Emba, Ovide B.; Ewango, Corneille E. N.; Girkin, Nicholas T.; Ifo, Suspense A.; Kanyama, Joseph T.; Mampouya, Yeto Emmanuel Wenina; Mbemba, Mackline; Ndjango, Jean-Bosco N.; Palmer, Paul I.; Sjögersten, Sofie; Lewis, Simon L.
    Inundation dynamics are the primary control on greenhouse gas emissions from peatlands. Situated in the central Congo Basin, the Cuvette Centrale is the largest tropical peatland complex. However, our knowledge of the spatial and temporal variations in its water levels is limited. By addressing this gap, we can quantify the relationship between the Cuvette Centrale’s water levels and greenhouse gas emissions, and further provide a baseline from which deviations caused by climate or land-use change can be observed, and their impacts understood. We present here a novel approach that combines satellite-derived rainfall, evapotranspiration and L-band Synthetic Aperture Radar (SAR) data to estimate spatial and temporal changes in water level across a sub-region of the Cuvette Centrale. Our key outputs are a map showing the spatial distribution of rainfed and flood-prone locations and a daily, 100 m resolution map of peatland water levels. This map is validated using satellite altimetry data and in situ water table data from water loggers. We determine that 50% of peatlands within our study area are largely rainfed, and a further 22.5% are somewhat rainfed, receiving hydrological input mostly from rainfall (directly and via surface/sub-surface inputs in sloped areas). The remaining 27.5% of peatlands are mainly situated in riverine floodplain areas to the east of the Congo River and between the Ubangui and Congo rivers. The mean amplitude of the water level across our study area and over a 20-month period is 22.8 ± 10.1 cm to 1 standard deviation. Maximum temporal variations in water levels occur in the riverine floodplain areas and in the inter-fluvial region between the Ubangui and Congo rivers. Our results show that spatial and temporal changes in water levels can be successfully mapped over tropical peatlands using the pattern of net water input (rainfall minus evapotranspiration, not accounting for run-off) and L-band SAR data.
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    A measurement-based verification framework for UK greenhouse gas emissions: an overview of the Greenhouse gAs Uk and Global Emissions (GAUGE) project
    (Elsevier, 2018-08-17) Palmer, Paul I.; O'Doherty, Simon; Allen, Grant; Bower, Keith; Bösch, Hartmut; Chipperfield, Martyn P.; Connors, Sarah; Dhomse, Sandip; Feng, Liang; Finch, Douglas P.; Gallagher, Martin W.; Gloor, Emanuel; Gonzi, Siegfried; Harris, Neil R. P.; Helfter, Carole; Humpage, Neil; Kerridge, Brian; Knappett, Diane; Jones, Roderic L.; Le Breton, Michael; Lunt, Mark F.; Manning, Alistair J.; Matthiesen, Stephan; Muller, Jennifer B. A.; Mullinger, Neil; Nemitz, Eiko; O'Shea, Sebastian; Parker, Robert J.; Percival, Carl J.; Pitt, Joseph; Riddick, Stuart N.; Rigby, Matthew; Sembhi, Harjinder; Siddans, Richard; Skelton, Robert L.; Smith, Paul; Sonderfeld, Hannah; Stanley, Kieran; Stavert, Ann R.; Wenger, Angelina; White, Emily; Wilson, Christopher; Young, Dickon
    We describe the motivation, design, and execution of the Greenhouse gAs Uk and Global Emissions (GAUGE) project. The overarching scientific objective of GAUGE was to use atmospheric data to estimate the magnitude, distribution, and uncertainty of the UK greenhouse gas (GHG, defined here as CO2, CH4, and N2O) budget, 2013–2015. To address this objective, we established a multi-year and interlinked measurement and data analysis programme, building on an established tall-tower GHG measurement network. The calibrated measurement network comprises ground-based, airborne, ship-borne, balloon-borne, and space-borne GHG sensors. Our choice of measurement technologies and measurement locations reflects the heterogeneity of UK GHG sources, which range from small point sources such as landfills to large, diffuse sources such as agriculture. Atmospheric mole fraction data collected at the tall towers and on the ships provide information on sub-continental fluxes, representing the backbone to the GAUGE network. Additional spatial and temporal details of GHG fluxes over East Anglia were inferred from data collected by a regional network. Data collected during aircraft flights were used to study the transport of GHGs on local and regional scales. We purposely integrated new sensor and platform technologies into the GAUGE network, allowing us to lay the foundations of a strengthened UK capability to verify national GHG emissions beyond the project lifetime. For example, current satellites provide sparse and seasonally uneven sampling over the UK mainly because of its geographical size and cloud cover. This situation will improve with new and future satellite instruments, e.g. measurements of CH4 from the TROPOspheric Monitoring Instrument (TROPOMI) aboard Sentinel-5P. We use global, nested, and regional atmospheric transport models and inverse methods to infer geographically resolved CO2 and CH4 fluxes. This multi-model approach allows us to study model spread in a posteriori flux estimates. These models are used to determine the relative importance of different measurements to infer the UK GHG budget. Attributing observed GHG variations to specific sources is a major challenge. Within a UK-wide spatial context we used two approaches: (1) Δ14CO2 and other relevant isotopologues (e.g. δ13CCH4) from collected air samples to quantify the contribution from fossil fuel combustion and other sources, and (2) geographical separation of individual sources, e.g. agriculture, using a high-density measurement network. Neither of these represents a definitive approach, but they will provide invaluable information about GHG source attribution when they are adopted as part of a more comprehensive, long-term national GHG measurement programme. We also conducted a number of case studies, including an instrumented landfill experiment that provided a test bed for new technologies and flux estimation methods. We anticipate that results from the GAUGE project will help inform other countries on how to use atmospheric data to quantify their nationally determined contributions to the Paris Agreement.
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    Quantifying the vertical transport of CHBr3 and CH2Br2 over the Western Pacific
    (Elsevier, 2018-09-12) Butler, Robyn; Palmer, Paul I.; Feng, Liang; Andrews, Stephen J.; Atlas, Elliot L.; Carpenter, Lucy J.; Donets, Valeria; Harris, Neil; Montzka, Stephen A.; Pan, Laura L.; Salawitch, Ross J.; Schauffler, Sue M.
    We use the GEOS-Chem global 3-D atmospheric chemistry transport model to interpret atmospheric observations of bromoform (CHBr3) and dibromomethane (CH2Br2) collected during the CAST and CONTRAST aircraft measurement campaigns over the western Pacific, January–February 2014. We use a new linearized, tagged version of CHBr3 and CH2Br2, allowing us to study the influence of emissions from specific geographical regions on observed atmospheric variations. The model describes 32 %–37 % of CHBr3 and 15 %–45 % of CH2Br2 observed variability during CAST and CONTRAST, reflecting model errors in vertical transport. The model has a mean positive bias of 30 % that is larger near the surface, reflecting errors in the poorly constrained prior emission estimates. We find using the model that observed variability of CHBr3 and CH2Br2 is driven by open ocean emissions where there is deep convection. Atmospheric variability above 6 km includes a significant contribution from coastal oceans, but it is still dominated by emissions from the open ocean and by older air masses that originate upwind. In the absence of reliable ocean emission estimates, we use a new physical age-of-air simulation to determine the relative abundance of halogens delivered by CHBr3 and CH2Br2 to the tropical transition layer (TTL). We find that 76 % (92 %) of air masses that originate from the ocean reach the TTL within two (three) atmospheric e-folding lifetimes of CHBr3 and almost all of them reach the TTL within one e-folding lifetime of CH2Br2. Over the duration of CAST and CONTRAST, and over our study region, oceans delivered a mean (range) CHBr3 and CH2Br2 mole fraction of 0.46 (0.13–0.72) and 0.88 (0.71–1.01) pptv, respectively, to the TTL, and a mean (range) Bry mole fraction of 3.14 (1.81–4.18) pptv from source gases to the upper troposphere.
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    Surface fluxes of bromoform and dibromomethane over the tropical western Pacific inferred from airborne in situ measurements
    (Atmospheric Chemistry and Physics, 2018-10-15) Feng, Liang; Palmer, Paul I.; Butler, Robyn; Andrews, Stephen J.; Atlas, Elliot L.; Carpenter, Lucy J.; Donets, Valeria; Harris, Neil R. P.; Salawitch, Ross J.; Pan, Laura L.; Schauffler, Sue M.
    We infer surface fluxes of bromoform (CHBr3) and dibromoform (CH2Br2) from aircraft observations over the western Pacific using a tagged version of the GEOS-Chem global 3-D atmospheric chemistry model and a maximum a posteriori inverse model. Using GEOS-Chem (GC) as an intermediary, we find that the distribution of a priori ocean emissions of these gases are reasonably consistent with observed atmospheric mole fractions of CHBr3 (r = 0.62) and CH2Br2 (r = 0.38). These a priori emissions result in a positive model bias in CHBr3 peaking in the marine boundary layer, but reproduce observed values of CH2Br2 with no significant bias by virtue of its longer atmospheric lifetime. Using GEOS-Chem, we find that observed variations in atmospheric CHBr3 are determined equally by sources over the western Pacific and those outside the study region, but observed variations in CH2Br2 are determined mainly by sources outside the western Pacific. Numerical closed-loop experiments show that the spatial and temporal distribution of boundary layer aircraft data have the potential to substantially improve current knowledge of these fluxes, with improvements related to data density. Using the aircraft data, we estimate aggregated regional fluxes of 3.6±0.3×108 and 0.7±0.1×108gmonth−1 for CHBr3 and CH2Br2 over 130–155°E and 0–12°N, respectively, which represent reductions of 20%–40% of the prior inventories by Ordóñez et al. (2012) and substantial spatial deviations from different a priori inventories. We find no evidence to support a robust linear relationship between CHBr3 and CH2Br2 oceanic emissions, as used by previous studies. We find that over regions with dense observation coverage, our choice of a priori inventory does not significantly impact our reported a posteriori flux estimates.