Fluxes of Atmospheric Greenhouse-Gases in Maryland (FLAGG-MD): Emissions of Carbon Dioxide in the Baltimore, MD-Washington, D.C. Area

To study emissions of CO₂ in the Baltimore, MD-Washington, D.C. (Balt-Wash) area, an aircraft campaign was conducted in February 2015, as part of the Fluxes of Atmospheric Greenhouse-Gases in Maryland (FLAGG-MD) project. During the campaign, elevated mole fractions of CO₂ were observed downwind of the urban center and local power plants. Upwind flight data and Hybrid Single Particle Lagrangian Integrated Trajectory (HYSPLIT) model analyses help account for the impact of emissions outside the Balt-Wash area. The accuracy, precision, and sensitivity of CO₂ emissions estimates based on the mass balance approach were assessed for both power plants and cities. Our estimates of CO₂ emissions from two local power plants agree well with their Continuous Emissions Monitoring Systems (CEMS) records. For the 16 power plant plumes captured by the aircraft, the mean percentage difference of CO₂ emissions was -0.3%. For the Balt-Wash area as a whole, the 1σ CO₂ emission rate uncertainty for any individual aircraft-based mass balance approach experiment was ±38%. Treating the mass balance experiments, which were repeated seven times within 9 days, as individual quantifications of the Balt-Wash CO₂ emissions, the estimation uncertainty was ±16% (standard error of the mean at 95% CL). Our aircraft-based estimate was compared to various bottom-up fossil fuel CO₂ (FFCO₂) emission inventories. Based on the FLAGG-MD aircraft observations, we estimate 1.9 ± 0.3 MtC of FFCO₂ from the Balt-Wash area during the month of February 2015. The mean estimate of FFCO₂ from the four bottom-up models was 2.2 ± 0.3 MtC.