Seasonal Variability in Local Carbon Dioxide Biomass Burning Sources Over Central and Eastern US Using Airborne In Situ Enhancement Ratios

Abstract

Abstract We present observations of local enhancements in carbon dioxide (CO 2 ) from local emissions sources over three eastern US regions during four deployments of the Atmospheric Carbon Transport‐America (ACT‐America) campaign between summer 2016 and spring 2018. Local CO 2 emissions were characterized by carbon monoxide (CO) to CO 2 enhancement ratios (i.e., ΔCO/ΔCO 2 ) in air mass mixing observed during aircraft transects within the planetary boundary layer. By analyzing regional‐scale variability of CO 2 enhancements as a function of ΔCO/ΔCO 2 enhancement ratios, observed relative contributions to CO 2 emissions were separated into fossil fuel and biomass burning (BB) regimes across regions and seasons. CO 2 emission contributions attributed to biomass burning (ΔCO/ΔCO 2 > 4%) were negligible during summer and fall in all regions but climbed to ∼9%–11% of observed combustion contributions in the South during winter and spring. Relative CO 2 fire emission trends matched observed winter and spring BB contributions, but conflictingly predicted similar levels of BB during the fall. Satellite fire data from MODIS and VIIRS suggested the use of higher spatial resolution fire data that might improve modeled BB emissions but were not able to explain the bulk of the discrepancy.