A Cost-Benefit Analysis Framework for Urban Methane Monitoring.

Despite recent advances in measurement and monitoring, methane (CH4) emissions remain challenging to resolve at subcity jurisdictions as needed to inform mitigation progress. Here we develop an Observation System Simulation Experiment (OSSE) for New York City (NYC) to test whether a small number of strategically located, fixed in situ CH4 measurement sites, together with existing sites, can effectively and accurately monitor NYC borough-level emissions. We identify candidate sites from tall, city-owned buildings screened for rooftop suitability and rank >300 network configurations by their ability to recover monthly borough-level emissions. Results show that the existing network improves coverage of Manhattan and Brooklyn relative to having no network at all, but performance remains limited in Staten Island and the Bronx. Adding a single site in either borough improves performance, while a three-site configuration spanning Staten Island, the Bronx, and Brooklyn captures most remaining gains, with little benefit beyond three sites. We also test a hypothetical set of observations from commercial aircraft profiles and find that these can provide annual city-scale constraints, especially when few or no urban sites exist, but are less effective than fixed sites for resolving month-to-month, borough-level variability. Together, the results demonstrate that borough-scale CH4 monitoring is feasible with a compact, purpose-built network within the context of a wider set of existing and background tower observations, and that OSSEs provide a low-cost way to design such systems before deploying instruments.