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

Joshua P Digangi,Yonghoon Choi,Kenneth J Davis,Bianca C Baier,Colm Sweeney,Glenn S Diskin,Zachary R Barkley,Thomas Lauvaux,Hannah S Halliday,John B Nowak,Sandip Pal,Sha Feng

doi:10.1029/2020jd034525

Abstract

AbstractWe present observations of local enhancements in carbon dioxide (CO2) 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 CO2 emissions were characterized by carbon monoxide (CO) to CO2 enhancement ratios (i.e., ΔCO/ΔCO2) in air mass mixing observed during aircraft transects within the planetary boundary layer. By analyzing regional‐scale variability of CO2 enhancements as a function of ΔCO/ΔCO2 enhancement ratios, observed relative contributions to CO2 emissions were separated into fossil fuel and biomass burning (BB) regimes across regions and seasons. CO2 emission contributions attributed to biomass burning (ΔCO/ΔCO2 > 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 CO2 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.

Highlights

Carbon dioxide (CO2) is a primary product of combustion and a relatively inert compound in the atmosphere, and total CO2 emissions collectively have a strong influence on global climate
NWF is weighted by the magnitude of the enhancement in CO2, and changes in the NWF distribution across various ΔCO/ΔCO2 enhancement ratios can be used to evaluate the relative contributions of those CO2 emission sources and their inferred combustion efficiency (CE)
The fossil fuel (FF) regime is defined as ΔCO/ΔCO2 enhancement ratios between 0% and 4%, and the biomass burning (BB) regime is defined as enhancement ratios greater than 4%

Summary

Introduction

Carbon dioxide (CO2) is a primary product of combustion and a relatively inert compound in the atmosphere, and total CO2 emissions collectively have a strong influence on global climate. Accurately quantifying the accumulation of atmospheric CO2 from its broad variety of sources is critical to predicting future trends in global temperature and climate. For CO2, fossil fuel combustion is one of the primary global anthropogenic sources, but sources range widely in terms of both spatial distribution and emission type (Gurney et al, 2020a). Biomass burning (BB) remains a difficult source to constrain due to its unpredictable timing and wide variety of vegetative fuels and burning conditions. Satellite measurements provide global coverage, but with limited spatial and temporal resolution as well as limited comparability with in situ measurements (Eldering et al, 2017; Yokota et al, 2009). Airborne measurements of CO2 bridge these two spatial regimes, providing data with high spatial resolution and comparability over a broad area, making them well suited for regional emission surveys

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