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<p>In this paper, we compare Orbiting Carbon Observatory 2 (OCO-2) measurements of column-averaged dry-air mole fractions (DMF) of <span class="inline-formula">CO₂</span> (<span class="inline-formula"><math xmlns="http://www.w3.org/1998/Math/MathML" id="M3" display="inline" overflow="scroll" dspmath="mathml"><mrow class="chem"><msub><mi>X</mi><mrow><msub><mi mathvariant="normal">CO</mi><mn mathvariant="normal">2</mn></msub></mrow></msub></mrow></math><span><svg:svg xmlns:svg="http://www.w3.org/2000/svg" width="25pt" height="14pt" class="svg-formula" dspmath="mathimg" md5hash="c3f445c5edc4903d978afd6d2d7f9d00"><svg:image xmlns:xlink="http://www.w3.org/1999/xlink" xlink:href="amt-15-6605-2022-ie00003.svg" width="25pt" height="14pt" src="amt-15-6605-2022-ie00003.png"/></svg:svg></span></span>) and its urban–rural differences against ground-based remote sensing data measured by the Munich Urban Carbon Column network (MUCCnet). Since April 2020, OCO-2 has regularly conducted target observations in Munich, Germany. Its target-mode data provide high-resolution <span class="inline-formula"><math xmlns="http://www.w3.org/1998/Math/MathML" id="M4" display="inline" overflow="scroll" dspmath="mathml"><mrow class="chem"><msub><mi>X</mi><mrow><msub><mi mathvariant="normal">CO</mi><mn mathvariant="normal">2</mn></msub></mrow></msub></mrow></math><span><svg:svg xmlns:svg="http://www.w3.org/2000/svg" width="25pt" height="14pt" class="svg-formula" dspmath="mathimg" md5hash="e8fbe8a4dbae0b122481ced632b45acf"><svg:image xmlns:xlink="http://www.w3.org/1999/xlink" xlink:href="amt-15-6605-2022-ie00004.svg" width="25pt" height="14pt" src="amt-15-6605-2022-ie00004.png"/></svg:svg></span></span> within a 15 <span class="inline-formula">km</span> <span class="inline-formula">×</span> 20 <span class="inline-formula">km</span> target field of view that is greatly suited for carbon emission studies from space in cities and agglomerated areas. OCO-2 detects urban <span class="inline-formula"><math xmlns="http://www.w3.org/1998/Math/MathML" id="M8" display="inline" overflow="scroll" dspmath="mathml"><mrow class="chem"><msub><mi>X</mi><mrow><msub><mi mathvariant="normal">CO</mi><mn mathvariant="normal">2</mn></msub></mrow></msub></mrow></math><span><svg:svg xmlns:svg="http://www.w3.org/2000/svg" width="25pt" height="14pt" class="svg-formula" dspmath="mathimg" md5hash="56d1dd2446d590e279163319e07c77ad"><svg:image xmlns:xlink="http://www.w3.org/1999/xlink" xlink:href="amt-15-6605-2022-ie00005.svg" width="25pt" height="14pt" src="amt-15-6605-2022-ie00005.png"/></svg:svg></span></span> with a root mean square different (RMSD) of less than 1 <span class="inline-formula">ppm</span> when compared to the MUCCnet reference site. OCO-2 target <span class="inline-formula"><math xmlns="http://www.w3.org/1998/Math/MathML" id="M10" display="inline" overflow="scroll" dspmath="mathml"><mrow class="chem"><msub><mi>X</mi><mrow><msub><mi mathvariant="normal">CO</mi><mn mathvariant="normal">2</mn></msub></mrow></msub></mrow></math><span><svg:svg xmlns:svg="http://www.w3.org/2000/svg" width="25pt" height="14pt" class="svg-formula" dspmath="mathimg" md5hash="ba7379f9e93d3aee596c7777a6c69629"><svg:image xmlns:xlink="http://www.w3.org/1999/xlink" xlink:href="amt-15-6605-2022-ie00006.svg" width="25pt" height="14pt" src="amt-15-6605-2022-ie00006.png"/></svg:svg></span></span> is biased high against the ground-based measurements. The close proximity of MUCCnet's five fully automated remote sensing sites enables us to compare spaceborne and ground-based <span class="inline-formula"><math xmlns="http://www.w3.org/1998/Math/MathML" id="M11" display="inline" overflow="scroll" dspmath="mathml"><mrow class="chem"><msub><mi>X</mi><mrow><msub><mi mathvariant="normal">CO</mi><mn mathvariant="normal">2</mn></msub></mrow></msub></mrow></math><span><svg:svg xmlns:svg="http://www.w3.org/2000/svg" width="25pt" height="14pt" class="svg-formula" dspmath="mathimg" md5hash="010fe77e23204290ee40e7fd28ff4a75"><svg:image xmlns:xlink="http://www.w3.org/1999/xlink" xlink:href="amt-15-6605-2022-ie00007.svg" width="25pt" height="14pt" src="amt-15-6605-2022-ie00007.png"/></svg:svg></span></span> in three urban areas of Munich separately (center, north, and west) by dividing the target field into three smaller comparison domains. Due to this more constrained collocation, we observe improved agreement between spaceborne and ground-based <span class="inline-formula"><math xmlns="http://www.w3.org/1998/Math/MathML" id="M12" display="inline" overflow="scroll" dspmath="mathml"><mrow class="chem"><msub><mi>X</mi><mrow><msub><mi mathvariant="normal">CO</mi><mn mathvariant="normal">2</mn></msub></mrow></msub></mrow></math><span><svg:svg xmlns:svg="http://www.w3.org/2000/svg" width="25pt" height="14pt" class="svg-formula" dspmath="mathimg" md5hash="a5f2192e98dcd07b46f422db28442e0e"><svg:image xmlns:xlink="http://www.w3.org/1999/xlink" xlink:href="amt-15-6605-2022-ie00008.svg" width="25pt" height="14pt" src="amt-15-6605-2022-ie00008.png"/></svg:svg></span></span> in all three comparison domains.</p> <p>For the first time, <span class="inline-formula"><math xmlns="http://www.w3.org/1998/Math/MathML" id="M13" display="inline" overflow="scroll" dspmath="mathml"><mrow class="chem"><msub><mi>X</mi><mrow><msub><mi mathvariant="normal">CO</mi><mn mathvariant="normal">2</mn></msub></mrow></msub></mrow></math><span><svg:svg xmlns:svg="http://www.w3.org/2000/svg" width="25pt" height="14pt" class="svg-formula" dspmath="mathimg" md5hash="6072d35368d575cc9fcdda8c1bcb2eb8"><svg:image xmlns:xlink="http://www.w3.org/1999/xlink" xlink:href="amt-15-6605-2022-ie00009.svg" width="25pt" height="14pt" src="amt-15-6605-2022-ie00009.png"/></svg:svg></span></span> gradients within one OCO-2 target field of view are evaluated against ground-based measurements. We compare <span class="inline-formula"><math xmlns="http://www.w3.org/1998/Math/MathML" id="M14" display="inline" overflow="scroll" dspmath="mathml"><mrow class="chem"><msub><mi>X</mi><mrow><msub><mi mathvariant="normal">CO</mi><mn mathvariant="normal">2</mn></msub></mrow></msub></mrow></math><span><svg:svg xmlns:svg="http://www.w3.org/2000/svg" width="25pt" height="14pt" class="svg-formula" dspmath="mathimg" md5hash="26636d0deaf11970e7c193cf208d2d11"><svg:image xmlns:xlink="http://www.w3.org/1999/xlink" xlink:href="amt-15-6605-2022-ie00010.svg" width="25pt" height="14pt" src="amt-15-6605-2022-ie00010.png"/></svg:svg></span></span> gradients in the OCO-2 target observations to gradients captured by collocated MUCCnet sites. Generally, OCO-2 detects elevated <span class="inline-formula"><math xmlns="http://www.w3.org/1998/Math/MathML" id="M15" display="inline" overflow="scroll" dspmath="mathml"><mrow class="chem"><msub><mi>X</mi><mrow><msub><mi mathvariant="normal">CO</mi><mn mathvariant="normal">2</mn></msub></mrow></msub></mrow></math><span><svg:svg xmlns:svg="http://www.w3.org/2000/svg" width="25pt" height="14pt" class="svg-formula" dspmath="mathimg" md5hash="72b0bfbeb80399ca9e4eb993615724ee"><svg:image xmlns:xlink="http://www.w3.org/1999/xlink" xlink:href="amt-15-6605-2022-ie00011.svg" width="25pt" height="14pt" src="amt-15-6605-2022-ie00011.png"/></svg:svg></span></span> in the same regions as the ground-based monitoring network. More than 90 % of the observed spaceborne gradients have the same orientation as the <span class="inline-formula"><math xmlns="http://www.w3.org/1998/Math/MathML" id="M16" display="inline" overflow="scroll" dspmath="mathml"><mrow class="chem"><msub><mi>X</mi><mrow><msub><mi mathvariant="normal">CO</mi><mn mathvariant="normal">2</mn></msub></mrow></msub></mrow></math><span><svg:svg xmlns:svg="http://www.w3.org/2000/svg" width="25pt" height="14pt" class="svg-formula" dspmath="mathimg" md5hash="001817821d82dd602c99d180eaf413f3"><svg:image xmlns:xlink="http://www.w3.org/1999/xlink" xlink:href="amt-15-6605-2022-ie00012.svg" width="25pt" height="14pt" src="amt-15-6605-2022-ie00012.png"/></svg:svg></span></span> gradients measured by MUCCnet. During our study, urban–rural enhancements are found to be in the range of 0.1 to 1 <span class="inline-formula">ppm</span>. The low urban–rural gradients of typically well below 1 <span class="inline-formula">ppm</span> in Munich during our study allow us to test OCO-2's lower detection limits for intra-urban <span class="inline-formula"><math xmlns="http://www.w3.org/1998/Math/MathML" id="M19" display="inline" overflow="scroll" dspmath="mathml"><mrow class="chem"><msub><mi>X</mi><mrow><msub><mi mathvariant="normal">CO</mi><mn mathvariant="normal">2</mn></msub></mrow></msub></mrow></math><span><svg:svg xmlns:svg="http://www.w3.org/2000/svg" width="25pt" height="14pt" class="svg-formula" dspmath="mathimg" md5hash="e8e2df11d6063e576b207cfe4754cf8d"><svg:image xmlns:xlink="http://www.w3.org/1999/xlink" xlink:href="amt-15-6605-2022-ie00013.svg" width="25pt" height="14pt" src="amt-15-6605-2022-ie00013.png"/></svg:svg></span></span> gradients. Urban <span class="inline-formula"><math xmlns="http://www.w3.org/1998/Math/MathML" id="M20" display="inline" overflow="scroll" dspmath="mathml"><mrow class="chem"><msub><mi>X</mi><mrow><msub><mi mathvariant="normal">CO</mi><mn mathvariant="normal">2</mn></msub></mrow></msub></mrow></math><span><svg:svg xmlns:svg="http://www.w3.org/2000/svg" width="25pt" height="14pt" class="svg-formula" dspmath="mathimg" md5hash="8d4a4cab4ae7f86218df1dbcbb957aed"><svg:image xmlns:xlink="http://www.w3.org/1999/xlink" xlink:href="amt-15-6605-2022-ie00014.svg" width="25pt" height="14pt" src="amt-15-6605-2022-ie00014.png"/></svg:svg></span></span> gradients recorded by the OCO-2 instruments and MUCCnet are strongly correlated (<span class="inline-formula"><i>R</i>²=0.68</span>) with each other and have an RMSD of 0.32 <span class="inline-formula">ppm</span>. A case study, which includes a comparison of one OCO-2 target overpass to WRF-GHG modeled <span class="inline-formula"><math xmlns="http://www.w3.org/1998/Math/MathML" id="M23" display="inline" overflow="scroll" dspmath="mathml"><mrow class="chem"><msub><mi>X</mi><mrow><msub><mi mathvariant="normal">CO</mi><mn mathvariant="normal">2</mn></msub></mrow></msub></mrow></math><span><svg:svg xmlns:svg="http://www.w3.org/2000/svg" width="25pt" height="14pt" class="svg-formula" dspmath="mathimg" md5hash="507899fcf3ffb3030e56b16f4f0fdeb7"><svg:image xmlns:xlink="http://www.w3.org/1999/xlink" xlink:href="amt-15-6605-2022-ie00015.svg" width="25pt" height="14pt" src="amt-15-6605-2022-ie00015.png"/></svg:svg></span></span>, reveals a similar distribution of enhanced <span class="inline-formula">CO₂</span> column abundances in Munich. In this study, we address OCO-2's capability to detect small-scale spatial <span class="inline-formula"><math xmlns="http://www.w3.org/1998/Math/MathML" id="M25" display="inline" overflow="scroll" dspmath="mathml"><mrow class="chem"><msub><mi>X</mi><mrow><msub><mi mathvariant="normal">CO</mi><mn mathvariant="normal">2</mn></msub></mrow></msub></mrow></math><span><svg:svg xmlns:svg="http://www.w3.org/2000/svg" width="25pt" height="14pt" class="svg-formula" dspmath="mathimg" md5hash="9ce0d77f3814b93ce4c3349dde52a239"><svg:image xmlns:xlink="http://www.w3.org/1999/xlink" xlink:href="amt-15-6605-2022-ie00016.svg" width="25pt" height="14pt" src="amt-15-6605-2022-ie00016.png"/></svg:svg></span></span> differences within one target observation. Our results suggest OCO-2's potential to assess anthropogenic emissions from space.</p>