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Accurate quantification of urban greenhouse gas (GHG) emissions can benefit from path-averaged, high-precision, high-temporal-resolution measurements that complement point sensors and passive remote sensing. Among open-path techniques, dual-comb spectroscopy (DCS) stands out as a particularly capable candidate, offering simultaneous broadband coverage, an absolute SI-traceable frequency axis, and sufficient spectral radiance for multi-kilometer paths. Here we present an open-path dual-comb spectrometer using two commercial, self-referenced, turn-key frequency combs operated continuously in Heidelberg, Germany, over an urban landscape. The instrument allows to infer column-averaged dry-air mole fractions of CO₂ along a 3.1 km absorption path. Within the evaluation period from September 2025 to February 2026 the system achieved a data coverage of 76 %, with losses primarily attributable to visibility-limiting weather conditions such as fog and heavy rain. The instrument precision, characterized by the overlapping Allan deviation under stable atmospheric conditions, reaches 6.13 ppm  for CO₂, equivalent to 0.35 ppm at 5 min averaging time. These values are on par with or better than previous open-path DCS experiments and represent roughly one order of magnitude improvement over a co-deployed open-path Fourier transform spectrometer operating on the same path. The two instruments differ by a small bias of 0.50 ppm for CO₂. These results demonstrate that commercial frequency-comb technology has matured enough to turn open-path DCS into an accessible tool for the broader atmospheric science community, without sacrificing performance: built exclusively from commercially available components, our instrument remains fully competitive with custom-built dual-comb spectrometers. This establishes a foundation for distributed path-averaged observations, from urban emission monitoring and network-scale deployments to the validation of spectroscopic databases.