Detectability of CO ₂ emission plumes of cities and power plants with the Copernicus Anthropogenic CO ₂ Monitoring (CO2M) mission

High-resolution atmospheric transport simulations were used to investigate the potential for detecting carbon dioxide (inline-formulaCO₂) plumes of the city of Berlin and neighboring power stations with the Copernicus Anthropogenic Carbon Dioxide Monitoring (CO2M) mission, which is a proposed constellation of inline-formulaCO₂ satellites with imaging capabilities. The potential for detecting plumes was studied for satellite images of inline-formulaCO₂ alone or in combination with images of nitrogen dioxide (inline-formulaNO₂) and carbon monoxide (CO) to investigate the added value of measurements of other gases coemitted with inline-formulaCO₂ that have better signal-to-noise ratios. The additional inline-formulaNO₂ and CO images were either generated for instruments on the same CO2M satellites (2 kminline-formula× 2 km resolution) or for the Sentinel-5 instrument (7.5 kminline-formula× 7.5 km) assumed to fly 2 h earlier than CO2M. Realistic inline-formulaCO₂, CO and inline-formula $M13inlinescrollmathmlchem{\mathrm{normal\; NO}}_X(=chem\mathrm{normal\; NO}+chem{\mathrm{normal\; NO}}_{\mathrm{normal\; 2}})$ 92pt13ptsvg-formulamathimg9e52e52845ffd38ac7454c4a0ec9f2c0 amt-12-6695-2019-ie00001.svg92pt13ptamt-12-6695-2019-ie00001.png fields were simulated at 1 kminline-formula× 1 km horizontal resolution with the Consortium for Small-scale Modeling model extended with a module for the simulation of greenhouse gases (COSMO-GHG) for the year 2015, and they were used as input for an orbit simulator to generate synthetic observations of columns of inline-formulaCO₂, CO and inline-formulaNO₂ for constellations of up to six satellites. A simple plume detection algorithm was applied to detect coherent structures in the images of inline-formulaCO₂, inline-formulaNO₂ or CO against instrument noise and variability in background levels. Although six satellites with an assumed swath of 250 km were sufficient to overpass Berlin on a daily basis, only about 50 out of 365 plumes per year could be observed in conditions suitable for emission estimation due to frequent cloud cover. With the inline-formulaCO₂ instrument only 6 and 16 of these 50 plumes could be detected assuming a high-noise (inline-formulaσ_VEG50=1.0 ppm) and low-noise (inline-formulaσ_VEG50=0.5 ppm) scenario, respectively, because the inline-formulaCO₂ signals were often too weak. A CO instrument with specifications similar to the Sentinel-5 mission performed worse than the inline-formulaCO₂ instrument, while the number of detectable plumes could be significantly increased to about 35 plumes with an inline-formulaNO₂ instrument. inline-formulaCO₂ and inline-formulaNO₂ plumes were found to overlap to a large extent, although inline-formulaNO_X had a limited lifetime (assumed to be 4 h) and although inline-formulaCO₂ and inline-formulaNO_X were emitted with different inline-formulaNO_X:CO₂ emission ratios by different source types with different temporal and vertical emission profiles. Using inline-formulaNO₂ observations from the Sentinel-5 platform instead resulted in a significant spatial mismatch between inline-formulaNO₂ and inline-formulaCO₂ plumes due to the 2 h time difference between Sentinel-5 and CO2M. The plumes of the coal-fired power plant Jänschwalde were easier to detect with the inline-formulaCO₂ instrument (about 40–45 plumes per year), but, again, an inline-formulaNO₂ instrument could detect significantly more plumes (about 70). Auxiliary measurements of inline-formulaNO₂ were thus found to greatly enhance the capability of detecting the location of inline-formulaCO₂ plumes, which will be invaluable for the quantification of inline-formulaCO₂ emissions from large point sources.