A ground-based remote sensing measurement network designed to infer net emission of CO2 and methane from the City of Edinburgh

Reducing emissions of greenhouse gases (GHGs) from urban areas – currently accounting for 70% of the global GHG emissions – are an integral part of the solution to meet net zero targets (IPCC, 2022). We have developed an observational framework to determine long-term trends in GHG emissions from the City of Edinburgh, Scotland, which has a 2030 net-zero (CO₂e) target. This is part of the GHG Emissions Monitoring network to Inform Net-zero Initiatives +Edinburgh (GEMINI+Edinburgh) which extends GEMINI-UK (Kurganskiy et al., 2025).

To determine city-wide net emission estimates of CO₂ and methane, we use column concentrations of CO₂ and methane retrieved from six EM27/SUN Fourier transform solar absorption spectrometers (“EM27”, Bruker GmbH, Germany) deployed in a ring around Edinburgh with 5 – 8 km separation. The spectrometers use the sun as their open-path source to measure solar radiation (4000 - 12000 cm^-1, 0.5 cm^-1 spectral resolution) to retrieve column abundances of CO₂, methane, CO, O₂, and H₂O. We apply an upwind-downwind mass balance approach to the data collected from the spectrometers to estimate city-wide net emissions. Spatial variations in near-surface wind fields are captured by eight automatic weather stations (Vaisala WXT530) and sonic anemometers (Gill WindSonic 75) co-located with each EM27 and on additional tall buildings.

We have developed methods to ensure that GEMINI+Edinburgh delivers long-term (O10 year) measurements and reliable GHG emission trends. As delivered, the EM27 is not weatherproof and not designed for unsupervised operation. We demonstrate the performance of a new weatherproof enclosure (Karn Scientific Ltd., Edinburgh) using co-located (un)enclosed EM27s. We employ a data processing workflow to enable long-term automated operation of the network, including an instrument meta data system, data transfer, processing, diagnostics plots, and archiving. We present preliminary data from the observation network since spring 2025 and propose strategies to communicate and evaluate Edinburgh’s net-zero progress.