G01_02

Tracking changes in fossil fuel CO₂ emissions using citizen science supported radiocarbon observations

Turnbull J^1,2, Domingues L¹, Turton N¹

¹GNS Science, Lower Hut, New Zealand, ²CIRES, University of Colorado, Boulder, USA

Emissions from on road transportation are one of the largest sources of fossil fuel CO₂ globally.  For many cities, they are the largest single emission source, and hence are a primary target for mitigation actions not only to reduce fossil fuel CO₂ emissions, but adding the co-benefits of reduced traffic, reduced reliance on fuel imports and cleaner air.

Mitigation strategies include improved vehicle efficiency, transition to electric vehicles, and traffic reduction strategies.

The travel and work restrictions imposed by COVID-19 lockdowns resulted in dramatic changes in fossil fuel CO₂ emissions around the world, most prominently in the transportation sector.  This provided an ideal opportunity to test our ability to observe and quantify local changes in fossil fuel CO₂ emissions.  We used a novel citizen science campaign to collect grass samples from around New Zealand and use radiocarbon measurements to quantify the recently added, local, fossil fuel CO₂ mole fraction at the local and time period that the grass grew. 

Our results from 17 sites in five cities around New Zealand demonstrate dramatic reductions in traffic emissions of 75 ± 3 % during the most severe lockdown restriction period.  The less restrictive 2021 lockdown resulted in spatially variable transportation emission reductions, apparently due to local traffic patterns and traffic flow. Overall, the grass sampling methodology gives surprisingly robust results, engages the community and policy makers, and provides a straightforward method for evaluating the impact of local-scale emission mitigation strategies.