• Energy Research

<p>Urban areas are recognised as a significant source of greenhouse gas emissions (GHG), such as carbon dioxide (CO<sub>2</sub>) and methane (CH<sub>4</sub>). The total amount of urban GHG emissions, especially for CH<sub>4</sub>, however, is not well quantified. Here we report on airborne in situ measurements using a Picarro G1301-m analyser aboard the DLR Cessna Grand Caravan to study GHG emissions downwind of the German capital city Berlin. In total, five aircraft-based mass balance experiments were conducted in July 2018 within the Urban Climate Under Change [UC]<sup>2</sup> project. The detection and isolation of the Berlin plume was often challenging because of comparatively small GHG signals above variable atmospheric background concentrations. However, on July 20<sup>th</sup> enhancements of up to 4 ppm CO<sub>2</sub> and 21 ppb CH<sub>4</sub> were observed over a horizontal extent of roughly 45 to 65 km downwind of Berlin. These enhanced mixing ratios are clearly distinguishable from the background and can partly be assigned to city emissions. The estimated CO<sub>2</sub> emission flux of 1.39 ± 0.75 t s<sup>-1 </sup>is in agreement with current inventories, while the CH<sub>4</sub> emission flux of 5.20 ± 1.61 kg s<sup>-1</sup> is almost two times larger than the highest reported value in the inventories. We localized the source area with HYSPLIT trajectory calculations and the high resolution numerical model MECO(n) (down to ~1 km), and investigated the contribution from sewage-treatment plants and waste deposition to CH<sub>4</sub>, which are treated differently by the emission inventories. Our work highlights the importance of a) strong CH<sub>4</sub> sources in the surroundings of Berlin and b) a detailed knowledge of GHG inflow mixing ratios to suitably estimate emission rates.</p>

Successful mitigation of air pollution in large cities requires information about the structure of emission sources and their contribution to total atmospheric load. The presented research demonstrates a possibility of application of isotope tracers for the estimation of contribution of different sources to the carbonaceous fraction of PM2.5 (Particulate Matter containing fraction below 2.5 μm) collected in the urban atmosphere of Krakow, Poland during the summer and winter seasons. Isotope mass balance approach was used to perform source apportionment analysis for those two seasons. The analysis showed that the dominant source of the carbonaceous fraction of PM2.5 in Krakow is coal burning during the winter season and biogenic emissions during the summer season. Sensitivity analysis revealed that the uncertainty of the percentage contribution of different sources to the overall carbon load of the analyzed PM2.5 fraction is in order of a few percent.