Carbon in the Capitol: DC Metro carbon dioxide monitoring in the COVID era

Carbon dioxide (CO2) is a critical greenhouse gas with concentrations at current values not seen for the past 2 million years. Due to the unprecedented large reductions in movement outside homes and general alterations to daily human activities, COVID-19 has led to drops in public and personal transport, although not commercial transport. These transport changes have important consequences for CO2 emissions especially in cities where people are concentrated.

To monitor these changes, we developed low-cost, novel CO2 sensors and deployed them May - July 2020 while Washington, DC was under lock-down due to COVID-19. The sensors measure CO2, temperature, pressure, and humidity every 5 minutes. We distributed 30 sensors at ground level (1-3 m above ground) across all 8 wards of DC in sites varying in vegetation cover, type of neighborhood (commercial versus residential), population density, proximity to major road infrastructure. Ground deployment allows us to relate local measures of CO2 to these local covariates in a highly replicated and distributed network. Sensors will continue logging for 2 years in hopes of measuring the city CO2 response as DC shifts between lock-down phases and the eventual reopening of the city.

To date, we have found differences in daily CO2 cycling patterns based on (1) distance to large-scale roadways and (2) local photosynthetic potential (LANDSAT-based NDVI). Sensors near low traffic concentrations and representing high NDVI have higher daily CO2 variability, with the highest CO2 values occurring at night. Sensors near high traffic concentrations and low NDVI have less daily variability, with noticeable spikes at 9 AM and 5 PM. Our results capture important interplays between both anthropogenic signals (i.e., transportation emissions) and natural signals (i.e., photosynthetic processes). Thus, we believe our results will be informative to researchers interested in urban greenhouse gas removal strategies.