Ground based Atmospheric Profiling of GreenHouse Gases (GAP-GHG)

The UK's target to reach net zero emissions by 2050 requires a coordinated approach to decarbonise all sectors. Transparent monitoring and verification are essential to manage progress towards this target and assess and inform reduction policies. To do so, "bottom-up" estimates of greenhouse gas (GHG) emissions must be significantly improved.

Similar to other industrialized nations, the UK needs to implement a complementary "top-down" GHG emission approach, where actual GHG concentration measurements from instrument networks, are assimilated with models to provide GHG surface emission estimates. The need is particularly acute at the local scale, where ad-hoc dense measurement networks are required to characterize specific settings and quantify their emissions.

Traditional GHG measurement networks are composed of in-situ point sensors on, or close to, the Earth's surface. More recently, remote sensing spectrometers operating in solar occultation mode have been deployed. In this configuration spectrometers view sunlight passing through the Earth's atmosphere to measure an integrated GHG concentration, from the top to the bottom of the atmosphere.

However, only the GHG concentrations in lower parts of the atmosphere are strongly coupled to surface emissions, and currently modelling must be used to infer emission sources. The Ground-based Atmospheric Profiling of GHG (GAP-GHG) project will develop, deploy and validate a miniature, cost-effective, spectrometer capable of making complementary measurements that give information on the vertical distribution of GHGs.

This additional information will improve our estimation of GHG emissions from particular sources by complementing, enhancing and validating models.

The ultimate goal of GAP-GHG is to demonstrate that this novel remote sensing instrument is capable of enhancing the UK's GHG emission monitoring systems. This development is particularly timely as the UK is setting up a remote sensing network as part of the GHG Emissions Measurement and Modelling Advancement (GEMMA) programme, through which the instrument's data could be exploited.

GAP-GHG is a first step towards this goal focusing on: 1) design, assembly, and laboratory characterization of an instrument targeting methane, 2) design and development of data processing software and 3) a twelve-month field campaign operating in a real-world environment to validate the instrument performance against an established international GHG monitoring network (the UK's Total Carbon Column Observatory Network site at Harwell, Oxfordshire).

The project will produce a methane dataset covering a complete seasonal cycle, that will be shared with the GEMMA programme and the wider research community to assess the potential value of the instrument as part of future GHG emission monitoring systems. Whilst the GAP-GHG project focuses on methane, the technology that underpins the instrument can target other GHG molecules, or atmospheric constituents relevant to air quality.

Although GAP-GHG is aimed at enhancing UK GHG monitoring capabilities, there is significant potential for the technology to be deployed internationally, complementing existing worldwide GHG monitoring networks.