A measurement-based verification framework for UK greenhouse gas emissions: an overview of the Greenhouse gAs Uk and Global Emissions (GAUGE) project
Authors: 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 
Published: August 2018

Abstract. 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.