Preprints
https://doi.org/10.5194/acp-2021-897
https://doi.org/10.5194/acp-2021-897

  04 Nov 2021

04 Nov 2021

Review status: this preprint is currently under review for the journal ACP.

Stable carbon isotopic composition of biomass burning emissions – implications for estimating the contribution of C3 and C4 plants

Roland Vernooij1, Ulrike Dusek2, Maria Elena Popa3, Peng Yao2, Anupam Shaikat2, Chenxi Qiu3,4, Patrik Winiger1,5, Carina van der Veen3, Tom Eames1, Natasha Ribeiro6, and Guido van der Werf1 Roland Vernooij et al.
  • 1Department of Earth Sciences, Faculty of Science, Vrije Universiteit Amsterdam, 1081 HV Amsterdam, the Netherlands
  • 2Centre for Isotope Research (CIO), Energy and Sustainability Research Institute Groningen (ESRIG), Rijksuniversiteit Groningen, the Netherlands
  • 3Institute for Marine and Atmospheric research Utrecht, Utrecht University, the Netherlands
  • 4Forschungszentrum Jülich GmbH, IEK-7, Jülich, Germany
  • 5Federal Institute of Technology (ETH) Zurich, Switzerland
  • 6Faculty of Agronomy and Forest Engineering, Eduardo Mondlane University, Maputo, Mozambique

Abstract. Landscape fires are a significant contributor to atmospheric burdens of greenhouse gases and aerosols. Although many studies have looked at biomass burning products and their fate in the atmosphere, estimating and tracing atmospheric pollution from landscape fires based on atmospheric measurements is challenging due to the large variability in fuel composition and burning conditions. Stable carbon isotopes in biomass burning (BB) emissions can be used to trace the contribution of C3 plants (e.g., trees or shrubs) and C4 plants (e.g. savanna grasses) to various combustion products. However, there are still many uncertainties regarding changes in isotopic composition (also known as fractionation) of the emitted carbon compared to the burnt fuel during the pyrolysis and combustion processes. To study BB isotope fractionation, we performed a series of laboratory fire experiments in which we burned pure C3 and C4 plants as well as mixtures of the two. Using isotope ratio mass spectrometry (IRMS), we measured stable carbon isotope signatures in the pre-fire fuels and post-fire residual char, as well as in the CO2, CO, CH4, organic carbon (OC), and elemental carbon (EC) emissions, which together constitute over 98 % of the post-fire carbon. Our laboratory tests indicated substantial isotopic fractionation in combustion products compared to the fuel, which varied between the measured fire products. CO2, EC and residual char were the most reliable tracers of the fuel 13C signature. CO in particular showed a distinct dependence on burning conditions; flaming emissions were enriched in 13C compared to smouldering combustion emissions. For CH4 and OC, the fractionation was opposite for C3 emissions (13C-enriched) and C4 emissions (13C-depleted). This indicates that while it is possible to distinguish between fires that were dominated by either C3 or C4 fuels using these tracers, it is more complicated to quantify their relative contribution to a mixed-fuel-fire based on the δ13C signature of emissions. Besides laboratory experiments, we sampled gases and carbonaceous aerosols from prescribed fires in the Niassa special Reserve (NSR) in Mozambique, using an unmanned aerial system (UAS)-mounted sampling set-up. We also provide a range of C3 : C4 contributions to the fuel and measured the fuel isotopic signatures. While both OC and EC were useful tracers of the C3 to C4 fuel ratio in mixed fires in the lab, we found particularly OC to be depleted compared to the calculated fuel signal in the field experiments. This suggests that either our fuel measurements were incomprehensive and underestimated the C3 : C4 ratio in the field, or that other processes caused this depletion. Although additional field measurements are needed, our results indicate that C3 vs C4 source ratio estimation is possible with most BB products, albeit with varying uncertainty ranges.

Roland Vernooij et al.

Status: open (until 18 Dec 2021)

Comment types: AC – author | RC – referee | CC – community | EC – editor | CEC – chief editor | : Report abuse

Roland Vernooij et al.

Roland Vernooij et al.

Viewed

Total article views: 183 (including HTML, PDF, and XML)
HTML PDF XML Total BibTeX EndNote
134 42 7 183 4 4
  • HTML: 134
  • PDF: 42
  • XML: 7
  • Total: 183
  • BibTeX: 4
  • EndNote: 4
Views and downloads (calculated since 04 Nov 2021)
Cumulative views and downloads (calculated since 04 Nov 2021)

Viewed (geographical distribution)

Total article views: 245 (including HTML, PDF, and XML) Thereof 245 with geography defined and 0 with unknown origin.
Country # Views %
  • 1
1
 
 
 
 
Latest update: 01 Dec 2021
Download
Short summary
Landscape fires are a major source of greenhouse gases and aerosols, particularly in sub-tropical savannas. Stable carbon isotopes in emissions can be used to trace the contribution of C3 plants (e.g., trees or shrubs) and C4 plants (e.g. savanna grasses) to greenhouse gasses and aerosols, if the process is well-understood. This helps us to link individual vegetation types to emissions, identify biomass burning emissions in the atmosphere and improve the reconstruction of historic fire regimes.
Altmetrics