CarbonWatch-Urban: Nationally consistent CO2 emissions information for all Aotearoa New Zealand urban areas

Emission mitigation policy is often enacted through international agreements and national policies, but mitigation action typically happens at the local and city scale.  City governments need to understand their emissions and sinks in order to ascertain the best mitigation actions, and evaluate their effectiveness.  Detailed, granular emissions information is vital to acheive these goals but remains largely unavailable. 

CarbonWatch-Urban is a new research programme that will provide granular and nationally consistent emissions information for every town and city in Aotearoa New Zealand, using a hybrid approach utilising bottom-up flux models and a variety of atmospheric observations.  We model anthropogenic emissions for nine sectors, distributed finely in space and time, and separately model the urban biogenic CO₂ fluxes.  We have instrumented Auckland, New Zealand’s largest city with in situ CO₂, CO, CH₄, COS and black carbon measurements, and flask measurements of ¹⁴CO₂.  These allow us to quantify and separate CO₂ into source sectors, and use an atmospheric inversion framework to evaluate and improve the bottom-up flux models.  To evaluate suburb scale fluxes, we are using micrometeorological methods at sites in Auckland and Christchurch, representing two quite different climate and geographic enviornments.  These results will also feed back into improving the bottom-up flux models.  We then apply the improved bottom-up flux models to all towns and cities in Aotearoa New Zealand, and use spot-check flask based campaigns to evaluate the robustness of the bottom-up flux estimates across a range of towns and cities. 

Together, these methods represent a tiered approach to provide robust, validated emission and sink information across the whole nation.