Reconciling the differences between a bottom-up and inverse-estimated FFCO 2 emissions estimate in a large US urban area

Kevin Gurney, Jianming Liang, Risa Patarasuk, Darragh O'Keeffe, Jianhua Huang, Maya Hutchins, Thomas Lauvaux, Jocelyn C. Turnbull, Paul B. Shepson

Research output: Contribution to journalArticle

14 Scopus citations

Abstract

The INFLUX experiment has taken multiple approaches to estimate the carbon dioxide (CO 2 ) flux in a domain centered on the city of Indianapolis, Indiana. One approach, Hestia, uses a bottom-up technique relying on a mixture of activity data, fuel statistics, direct flux measurement and modeling algorithms. A second uses a Bayesian atmospheric inverse approach constrained by atmospheric CO 2 measurements and the Hestia emissions estimate as a prior CO 2 flux. The difference in the central estimate of the two approaches comes to 0.94 MtC (an 18.7% difference) over the eight-month period between September 1, 2012 and April 30, 2013, a statistically significant difference at the 2-sigma level. Here we explore possible explanations for this apparent discrepancy in an attempt to reconcile the flux estimates. We focus on two broad categories: 1) biases in the largest of bottom-up flux contributions and 2) missing CO 2 sources. Though there is some evidence for small biases in the Hestia fossil fuel carbon dioxide (FFCO 2 ) flux estimate as an explanation for the calculated difference, we find more support for missing CO 2 fluxes, with biological respiration the largest of these. Incorporation of these differences bring the Hestia bottom-up and the INFLUX inversion flux estimates into statistical agreement and are additionally consistent with wintertime measurements of atmospheric 14 CO 2 . We conclude that comparison of bottom-up and top-down approaches must consider all flux contributions and highlight the important contribution to urban carbon budgets of animal and biotic respiration. Incorporation of missing CO 2 fluxes reconciles the bottom-up and inverse-based approach in the INFLUX domain.

Original languageEnglish (US)
Article number44
JournalElementa
Volume5
DOIs
StatePublished - Jan 1 2017
Externally publishedYes

Keywords

  • Carbon flux
  • Carbon footprint
  • Fossil fuel CO2

ASJC Scopus subject areas

  • Oceanography
  • Environmental Engineering
  • Ecology
  • Geotechnical Engineering and Engineering Geology
  • Geology
  • Atmospheric Science

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    Gurney, K., Liang, J., Patarasuk, R., O'Keeffe, D., Huang, J., Hutchins, M., Lauvaux, T., Turnbull, J. C., & Shepson, P. B. (2017). Reconciling the differences between a bottom-up and inverse-estimated FFCO 2 emissions estimate in a large US urban area Elementa, 5, [44]. https://doi.org/10.1525/elementa.137