Atmospheric network requirements to detect policy-driven urban CO 2 emission changes

Abstract Subnational governments, particularly municipalities, play a crucial role in mitigating greenhouse gas emissions and advancing climate policy objectives. Atmospheric monitoring networks are essential for tracking emission trends and assessing the effectiveness of climate policies, assuming sufficient detectability across the designated metropolitan area. This study focuses on the capacity of an urban atmospheric monitoring network in and around Paris to effectively monitor CO 2 emission changes over time. By combining a high-resolution dynamic emissions inventory with an atmospheric transport model, we analyze the ability of monitoring networks to detect and track projected CO 2 emission changes derived from the latest Paris Climate Action Plan. The study goes beyond conventional accuracy targets by introducing detection limits based on actual climate policy goals mapped at high spatial resolution. By comparing the CO 2 fossil-fuel signals to the different error terms, such as background error, model error, and instrument error, we show that the current atmospheric monitoring network, with 9 high-precision and 21 medium-precision instruments, is able to detect and track future urban CO 2 emissions changes. High-precision analyzers provide sufficient information to detect wintertime emissions until 2050, while medium-precision sensors maintain effectiveness until 2035–2045. However, challenges persist in detecting summertime emissions due to uncertainties in background concentrations and significant biogenic flux perturbations, particularly in rural areas. Results also point to the importance of improving the background error characterization to enhance the effectiveness of atmospheric networks in monitoring emissions trends. Overall, our results provide insights into optimizing sensor placement, particularly the use of medium-precision sensors, which are limited to dense urban areas where fossil-fuel emissions’ signals are sufficiently large. By providing insights into the potentials and limitations of current atmospheric monitoring networks in tracking emissions trends, this study contributes to ongoing efforts to accompany robust climate policies and achieve climate-neutrality targets at the local level.