Title: Urban greenhouse gas measurements for science and policy
Abstract: Cities are often leading the way in CO2 emission mitigation efforts, both to address the climate challenge and the many associated co-benefits for urban areas. They want to understand their emissions both to assess the potential of carbon mitigation strategies and to evaluate the success of such strategies. Commonly, national-level CO2 reporting is downscaled to provide city-scale emission estimates. Different downscaling methods can produce differences of 50-100% for an individual city, too uncertain to provide meaningful guidance on typical emission reduction targets of 20-30%.
The long-running Indianapolis Flux Experiment (INFLUX) aims to develop and assess methods to constrain urban greenhouse gas emissions that be applied to cities around the world. INFLUX brings together new high-resolution (in both space and time) inventory assessments, a multi-year record of in situ CO2, CH4 and CO from tower-based and aircraft-based atmospheric measurements along with a complementary suite of 50 trace gases and isotopes from flasks, and atmospheric modelling. Together, these provide high-accuracy, high-resolution, continuous monitoring of GHG emissions from the city. I compare the bottom-up data product, and top-down tower-based atmospheric inversion and aircraft-based mass balance, in combination with flask observations of radiocarbon in CO2, to show that urban fossil fuel CO2 emissions can be constrained to better than 10%, sufficient to allow assessment of proposed emission reduction targets.
A new study in Auckland, New Zealand, uses lessons learned from INFLUX and other studies to tailor the research design and outputs to address the most pressing stakeholder questions and data gaps. We work collaboratively with Auckland Council and New Zealand’s Ministry for the Environment, leading to an immediate focus on the partitioning of Auckland’s CO2 fluxes into fossil fuel and land carbon exchange.