Using eddy-covariance to measure the effects of COVID-19 restrictions on CO₂ emissions in a neighborhood of Indianapolis, IN

Eddy-covariance (EC) flux measurements in Indianapolis were used to quantify the impact of the COVID-19 lockdown on CO and CO₂ emissions from a highway and a suburban neighborhood. CO₂ fluxes were measured for 6 weeks pre-lockdown (January 22, 2020–March 3, 2020) and during lockdown (March 25, 2020– May 5, 2020) using EC instrumentation at 41 m AGL. Fossil fuel CO₂ emissions (CO₂ff) were estimated by calculating eddy diffusivity to obtain CO flux and then scaling by the CO:CO₂ff emissions ratio (R_CO). Flux measurements segregated by wind direction were compared to hourly emissions from the 2020 Hestia inventory model. The lockdown CO₂ff average weekday emissions from the highway estimated by EC decreased by 51.5 ± 10.9% (11.2 ± 2.2 µmol m⁻² s⁻¹) compared to pre-lockdown, similar to Hestia’s estimate 56 ± 7% (12 ± 1 µmol m⁻² s⁻¹). The EC measurements detected a significant (2.2 ± 0.7 µmol m⁻² s⁻¹) but smaller magnitude decrease in CO₂ff emissions from the suburban neighborhood. The daily cycles of CO₂ff emissions were significantly correlated with Hestia estimates from the highway but not from the suburbs. This study demonstrates that EC flux towers and high-resolution inventory models in regions with mixed and spatially heterogeneous sources can quantify abrupt changes in sector- and source-specific CO₂ fluxes.