Remote sensing of columnar trace gases during the Ruisdael Rotterdam campaign in 2022

Urban areas are home to many people on the globe, and centres of industry. Emissions from cities contribute to atmospheric concentrations of greenhouse gases like CO₂ and CH₄, which influence the Earth’s energy budget. The Ruisdael Observatory is a Dutch research infrastructure to investigate the atmosphere over the Netherlands by bringing together measurements and high resolution modelling. One part of it is a semi-mobile trailer to be flexibly deployed as measurement station for targeted field measurements. Mounted on the roof of this trailer are a Bruker EM27/SUN (EM27) for columnar trace gas measurements and a Cimel for columnar aerosol measurements. A targeted field campaign was conducted in August and September 2022 to study Rotterdam, one of the biggest city in the Netherlands and the biggest harbour in Europe. Three EM27s were set up around Rotterdam in an upwind-downwind configuration. To ensure the comparability of the data, the instruments measured in parallel for three days before and after the measurement period, which showed good agreement between the instruments. Four different configurations of instrument locations were used during the three week campaign to account for changes in wind direction and investigate specific targets as well as separate between the influence of the harbour area and the city itself. Enhancements in the CO₂ column were around 1-3 ppm across the harbour and about 1 ppm across the city. CH₄ columnar concentrations were not significantly enhanced across the city, but increased by several ppb across the harbour area. The CO columnar concentrations increased across the harbour by up to 10 ppb and 5 ppb across the city area.