the Creative Commons Attribution 4.0 License.
the Creative Commons Attribution 4.0 License.
| 01 Nov 2022
Measurement report: Emission factors of NH3 and NHx for wildfires and agricultural fires in the United States
Laura Tomsche
Felix Piel
Tomas Mikoviny
Claus J. Nielsen
Hongyu Guo
Pedro Campuzano-Jost
Benjamin A. Nault
Melinda K. Schueneman
Jose L. Jimenez
Hannah Halliday
Glenn S. Diskin
Joshua P. DiGangi
John B. Nowak
Elizabeth B. Wiggins
Emily Gargulinski
Amber J. Soja
Armin Wisthaler
Abstract. During the 2019 Fire Influence on Regional to Global Environments and Air Quality (FIREX-AQ) study, the NASA DC-8 carried out in situ chemical measurements in smoke plumes emitted from wildfires and agricultural fires in the contiguous US. The DC-8 payload included a modified proton-transfer-reaction time-of-flight mass spectrometer (PTR-ToF-MS) for the fast measurement of gaseous ammonia (NH3) and a high-resolution time-of-flight aerosol mass spectrometer (AMS) for the fast measurement of submicron particulate ammonium (NH4+). We herein report data collected in smoke plumes emitted from six wildfires in the Western US, two prescribed grassland fires in the Central US, one prescribed forest fire in the Southern US, and 66 small agricultural fires in the Southeastern US. Smoke plumes contained double to triple digit ppb levels of NH3. In the wildfire plumes, a significant fraction of NH3 had already been converted to NH4+ at the time of sampling (≥2 h after emission). Substantial amounts of NH4+ were also detected in freshly emitted smoke from corn and rice field fires. We herein present a comprehensive set of emission factors of NH3 and NHx, with NHx = NH3 + NH4+. Average NH3 and NHx emission factors for wildfires in the Western US were 1.86 ± 0.75 g kg-1 of fuel burned and 2.47 ± 0.80 g kg-1, respectively. Average NH3 and NHx emission factors for agricultural fires in the Southeastern US were 0.89 ± 0.58 g kg-1 and 1.74 ± 0.92 g kg-1, respectively. Our data show no clear inverse correlation between modified combustion efficiency (MCE) and NH3 emissions. Importantly, we found that NH3 emissions in ambient sampling were significantly higher than observed in previous laboratory experiments with similar fuel types.
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Notice on discussion status
The requested preprint has a corresponding peer-reviewed final revised paper. You are encouraged to refer to the final revised version.
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Preprint
(1134 KB)
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Supplement
(498 KB)
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The requested preprint has a corresponding peer-reviewed final revised paper. You are encouraged to refer to the final revised version.
- Preprint
(1134 KB) -
Supplement
(498 KB) - BibTeX
- EndNote
- Final revised paper
Journal article(s) based on this preprint
Laura Tomsche et al.
Interactive discussion
Status: closed
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RC1: 'Comment on egusphere-2022-879', Anonymous Referee #1, 15 Dec 2022
The measurement report by Tomsche et al. presents data on NH3 and NHx emissions from multiple types of fires. The emission factors were generated using high-resolution observations of NH3 and NH4+ conducted via airplane campaigns. There is only one potential major issue with the paper and I recommend publishing with minor revisions, presented below.
The only major issue is stated in line 100 - in field calibrations were inconsistent. It's not clear how much of an issue this is, but anytime a calibration fails in situ one is concerned about the quality of the data. The authors need to provide more detail so this concern can be alleviated. How confident are they that the measurements are accurate based on the laboratory calibration.
In the introduction, line 59- it would be useful to provide more information to the reader on the differences of the Innsbruck instrument to the other instruments discussed in the paragraph.
Section 2.2 - The authors should provide some evidence to support the statement on line 87 that the instrumental background was reduced to single digit ppb levels.
Line 111 - what are the implications of the 34% uncertainty in the NH4+ data on the final calculated emissions factors? Can that uncertainty somehow be propagated through?
Line 114 - There is potentially a lot of organic N compounds in burning emissions (e.g., Mace et al., 2003 Water-soluble organic nitrogen in Amazon Basin aerosols during the dry (biomass burning) and wet seasons). This could be contributing to the large amount of NH4+ measured early on in the fires. This needs to be stated very clearly throughout the paper as the authors have no way of knowing if this is an issue or not.
Section 2.3 - is this the most commonly used method for calculating EFNH3? Also, why was the carbon fraction assumed to be 0.5? This should be justified.
Conclusions on line 215 - If the discrepancy is based on the tailing and downwind data, then the authors could prove that by doing the calculation on their data excluding tailing and the downwind data. This would provide confidence in the conclusions.
Citation: https://doi.org/10.5194/egusphere-2022-879-RC1 - AC1: 'Reply on RC1', Armin Wisthaler, 24 Jan 2023
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RC2: 'Comment on egusphere-2022-879', Anonymous Referee #2, 27 Dec 2022
General comments
Tomsche et al. present a measurement report of NH3 and NH4+ during an aircraft campaign (FIREX-AQ 2019) and derive their emission factors (EF). They find higher EFNH3 than laboratory measurements indicate for a variety of biomass burning conditions.
This work is topical due to the important role of reduced nitrogen in our atmosphere being increasingly recognized, significant due to the dearth of EFs from field measurements, and fits well within the scope of ACP.
Although the manuscript is concise, easy to read, and results are presented in a logically structured manner, there are some concerns that upon addressal may warrant its publication. These concerns, broadly regarding the lack of sufficient details and uncertainty analysis, are detailed below.
Specific comments
The EFs are reported as X ± Y g·kg−1. It is unclear what the plus/minus value refers to. Is this 1σ or some other value? Does this reflect the variability across multiple transects alone, the uncertainties in variables and assumed values in the EF calculation, or both? This needs to be clearly described in the Methods. [Also, Reviewer #1’s comment on propagated uncertainties.]
An assumed carbon fraction of 0.5 for biomass may be conservatively off by ±10% (please also cite literature justifying this assumption). [Also noted by Reviewer #1]
How was the background mixing ratio estimated? What about during agricultural fires, where there may have been numerous such occurring around the same time and around the same place contributing to NH3/NH4+ in the sampled air; can elevated VMRs specific to the plume under consideration be reliably obtained?
Which plume transect segments were used in the analyses? Ideally, also plot the selected transects on the map showing location of fires (at least for the wildfires).
How were the classifications by fuel types obtained?
Lines 212-217: Since Gkatzelis et al. (2022) cited here is unpublished, unavailable as a preprint, and not made available at the time of the review, these lines cannot be reviewed. Suggest deleting or making Gkatzelis et al. (2022) available during the next round of revisions.
Suggest avoiding speculative statements such as: (Conclusions) “NH3 emissions were highest from fires of corn and rice residues, which may be caused by fertilization of these fields.” There was no analysis presented to make this claim (even if softened by “may”).
The primary finding is that EFNH3 may be underestimated in laboratory studies. More details are required to develop confidence in the reader that this is the case. It may be that in the “real world conditions” there is burning/heating of duff and/or of the soil itself (NH4+ and NH4+ → NH3) that is not considered in the lab among other possible factors. That these are insignificant aspects and that lab- and aircraft-derived EFs are equivalent but not equal needs to be demonstrated before the finding is presented as strongly as it is in the manuscript.
Technical corrections
Throughout the manuscript: ppb or ppbV and ppm or ppmV?
The supplementary figures and tables are important for the narrative. Suggest moving these to the main manuscript and not relegating to the supplement.
Figure 1: The error shading seems to consider only the average values (circles) and not their error ranges as well. Why? Please also describe what exactly the shading represents in the figure caption.
Suggestion: Due to wide range of values in Figs. 1 and 2b, suggestion to use log-log scale.
Citation: https://doi.org/10.5194/egusphere-2022-879-RC2 - AC2: 'Reply on RC2', Armin Wisthaler, 24 Jan 2023
Interactive discussion
Status: closed
-
RC1: 'Comment on egusphere-2022-879', Anonymous Referee #1, 15 Dec 2022
The measurement report by Tomsche et al. presents data on NH3 and NHx emissions from multiple types of fires. The emission factors were generated using high-resolution observations of NH3 and NH4+ conducted via airplane campaigns. There is only one potential major issue with the paper and I recommend publishing with minor revisions, presented below.
The only major issue is stated in line 100 - in field calibrations were inconsistent. It's not clear how much of an issue this is, but anytime a calibration fails in situ one is concerned about the quality of the data. The authors need to provide more detail so this concern can be alleviated. How confident are they that the measurements are accurate based on the laboratory calibration.
In the introduction, line 59- it would be useful to provide more information to the reader on the differences of the Innsbruck instrument to the other instruments discussed in the paragraph.
Section 2.2 - The authors should provide some evidence to support the statement on line 87 that the instrumental background was reduced to single digit ppb levels.
Line 111 - what are the implications of the 34% uncertainty in the NH4+ data on the final calculated emissions factors? Can that uncertainty somehow be propagated through?
Line 114 - There is potentially a lot of organic N compounds in burning emissions (e.g., Mace et al., 2003 Water-soluble organic nitrogen in Amazon Basin aerosols during the dry (biomass burning) and wet seasons). This could be contributing to the large amount of NH4+ measured early on in the fires. This needs to be stated very clearly throughout the paper as the authors have no way of knowing if this is an issue or not.
Section 2.3 - is this the most commonly used method for calculating EFNH3? Also, why was the carbon fraction assumed to be 0.5? This should be justified.
Conclusions on line 215 - If the discrepancy is based on the tailing and downwind data, then the authors could prove that by doing the calculation on their data excluding tailing and the downwind data. This would provide confidence in the conclusions.
Citation: https://doi.org/10.5194/egusphere-2022-879-RC1 - AC1: 'Reply on RC1', Armin Wisthaler, 24 Jan 2023
-
RC2: 'Comment on egusphere-2022-879', Anonymous Referee #2, 27 Dec 2022
General comments
Tomsche et al. present a measurement report of NH3 and NH4+ during an aircraft campaign (FIREX-AQ 2019) and derive their emission factors (EF). They find higher EFNH3 than laboratory measurements indicate for a variety of biomass burning conditions.
This work is topical due to the important role of reduced nitrogen in our atmosphere being increasingly recognized, significant due to the dearth of EFs from field measurements, and fits well within the scope of ACP.
Although the manuscript is concise, easy to read, and results are presented in a logically structured manner, there are some concerns that upon addressal may warrant its publication. These concerns, broadly regarding the lack of sufficient details and uncertainty analysis, are detailed below.
Specific comments
The EFs are reported as X ± Y g·kg−1. It is unclear what the plus/minus value refers to. Is this 1σ or some other value? Does this reflect the variability across multiple transects alone, the uncertainties in variables and assumed values in the EF calculation, or both? This needs to be clearly described in the Methods. [Also, Reviewer #1’s comment on propagated uncertainties.]
An assumed carbon fraction of 0.5 for biomass may be conservatively off by ±10% (please also cite literature justifying this assumption). [Also noted by Reviewer #1]
How was the background mixing ratio estimated? What about during agricultural fires, where there may have been numerous such occurring around the same time and around the same place contributing to NH3/NH4+ in the sampled air; can elevated VMRs specific to the plume under consideration be reliably obtained?
Which plume transect segments were used in the analyses? Ideally, also plot the selected transects on the map showing location of fires (at least for the wildfires).
How were the classifications by fuel types obtained?
Lines 212-217: Since Gkatzelis et al. (2022) cited here is unpublished, unavailable as a preprint, and not made available at the time of the review, these lines cannot be reviewed. Suggest deleting or making Gkatzelis et al. (2022) available during the next round of revisions.
Suggest avoiding speculative statements such as: (Conclusions) “NH3 emissions were highest from fires of corn and rice residues, which may be caused by fertilization of these fields.” There was no analysis presented to make this claim (even if softened by “may”).
The primary finding is that EFNH3 may be underestimated in laboratory studies. More details are required to develop confidence in the reader that this is the case. It may be that in the “real world conditions” there is burning/heating of duff and/or of the soil itself (NH4+ and NH4+ → NH3) that is not considered in the lab among other possible factors. That these are insignificant aspects and that lab- and aircraft-derived EFs are equivalent but not equal needs to be demonstrated before the finding is presented as strongly as it is in the manuscript.
Technical corrections
Throughout the manuscript: ppb or ppbV and ppm or ppmV?
The supplementary figures and tables are important for the narrative. Suggest moving these to the main manuscript and not relegating to the supplement.
Figure 1: The error shading seems to consider only the average values (circles) and not their error ranges as well. Why? Please also describe what exactly the shading represents in the figure caption.
Suggestion: Due to wide range of values in Figs. 1 and 2b, suggestion to use log-log scale.
Citation: https://doi.org/10.5194/egusphere-2022-879-RC2 - AC2: 'Reply on RC2', Armin Wisthaler, 24 Jan 2023
Peer review completion
Journal article(s) based on this preprint
Laura Tomsche et al.
Data sets
Fire Influence on Regional to Global Environments and Air Quality NASA https://doi.org/10.5067/SUBORBITAL/FIREXAQ2019/DATA001
Laura Tomsche et al.
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The requested preprint has a corresponding peer-reviewed final revised paper. You are encouraged to refer to the final revised version.
- Preprint
(1134 KB) - Metadata XML
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Supplement
(498 KB) - BibTeX
- EndNote
- Final revised paper