the Creative Commons Attribution 4.0 License.
the Creative Commons Attribution 4.0 License.
| 23 Oct 2026
Molecular Composition of Oxygenated Nitrogen-Containing Organic Compounds Emitted from Combustion of the Three Biomass Macro-Components
Abstract. Biomass burning is an important source of oxygenated nitrogen-containing organic compounds, but their formation mechanisms remain unclear. CHON compounds in organic aerosols (OAs) from cellulose, hemicellulose, and lignin combustion at three ignition temperatures (IGT) under full-oxygen conditions were characterized by high-resolution mass spectrometry in negative and positive electrospray ionization modes. Our results indicate that CHON– and CHON+ compounds account for 13–60% and 3.4–32% of OA intensity, respectively, with the composition depending strongly on fuel type and IGT. Lignin-derived CHON compounds had higher aromatic fractions than cellulose- and hemicellulose-derived CHON compounds at low IGT, and all of them had high fractions of reduced-N species with high N contents. With the increasing IGT to 600 °C, the fractions of aromatic CHON increased for OAcellulose and OAhemicellulose but not for OAlignin, However, the molecular overlap of CHON compounds among the three OAs elevated, resulting in high similarity in the composition of nitro-phenolic-like compounds. More reduced-N aromatic compounds were produced at 800 °C for all fuels, but lignin yielded abundant condensed aromatic species. Our findings provide molecular-level insight into CHON chemodiversity across fuel types, and are beneficial for assess the climate and health effects of biomass burning OAs accurately.
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Status: open (until 04 Dec 2026)
- RC1: 'Comment on egusphere-2026-6389', Anonymous Referee #1, 09 Nov 2026 reply
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- 1
This manuscript uses HRMS to compare particulate CHON profiles from cellulose, hemicellulose, and lignin burned separately at furnace setpoints of 400, 600, and 800 °C. The experiments provide a controlled comparison of how the detected profiles vary with fuel and furnace combution temperature (IGT). My main concern is how far the results from these commercial materials can be extended to practical and whole biomass. The conclusion already acknowledges possible interactions among the three components. Please also discuss the contribution of other nitrogen-bearing constituents in native biomass, including proteins, and how differences in fuel nitrogen may affect comparisons with wood and straw combustion.
Major comments:
1. Combustion atmosphere (lines 19, 89–91, and 100–108). The abstract and introduction describe “full-oxygen conditions,” while Section 2.1 reports 20% oxygen. Please specify the oxygen fraction and the balance gas at the furnace inlet. Clarify whether “full-oxygen conditions” refers to an excess oxygen supply and use consistent terminology throughout the manuscript.
2. Fuel composition and nitrogen source (lines 100–101, 159–162, and 195–205). Please report the elemental composition of each commercial fuel used in the experiments, particularly its total nitrogen content. What species are meant by “inorganic nitrogen in the gas atmosphere” at line 196? If this refers to N2, please explain the evidence for its conversion to reactive nitrogen under the experimental conditions. Please also clarify whether NOₓ was measured during these burns and what evidence supports its proposed role in forming lignin-derived CHON compounds.
3. Gas monitoring and particle-phase O/C (Section 2.1 and lines 183–205). Figure S1 shows CO and CO2 monitors and a carbonyl sampling line. Section 2.1 cites the figure for the experimental setup, but the main text does not describe the gas measurements for the burns analyzed here. Please state which gases were measured and explain how the modified combustion efficiencies in Table S1 were obtained. If CO, CO2, or low-molecular-weight oxygenate data are available for these burns, please discuss how they inform the proposed explanation for the generally lower intensity-weighted CHON O/C ratios at higher setpoints for cellulose and hemicellulose.
4. Structural assignments and reduced nitrogen (lines 208–224, Figure 3, and lines 26–28). Please distinguish the assigned elemental formulas from the tentative functional groups and aromatic ring classes inferred from them. For example, a single-N formula with O/N = 2 can contain a nitro group, and a formula detected in both ESI modes can represent different isomers. Please justify the O/N < 3 criterion and clarify its relationship to the region labeled reduced-N in Figure 3, where ((O-2N)/C<0) corresponds to O/N < 2. Does the trend at 800 °C hold under both criteria and when single-N and multi-N formulas are examined separately?
The abstract states that more reduced-N aromatic compounds were produced at 800 °C. Please provide structural evidence for representative peaks that drive this result and quantitative support for an increase in the amount emitted. If the evidence is based on formula assignments and relative ion intensities, describe the result in terms of the relative signal of the formulas that meet the stated O/N and aromaticity criteria.
5. Temperature comparisons and reported percentages (Figure 1, Table S1, and lines 421–423). Please specify which IGT are being compared in the conclusion. In positive mode, the CHON fractions for cellulose are 4.3%, 8.1%, and 6.9% at 400, 600, and 800 °C, respectively. The corresponding lignin fractions are 29%, 32%, and 11%. Both series peak at 600 °C. Please also reconcile the negative-mode percentages in Figure 1 with Table S1. For cellulose at 400 °C, the figure shows 14%, which matches the formula-count percentage in Table S1, while the table gives 1.3% by ion intensity.
Minor comments:
1. Introduction (lines 33–97). Please focus the Introduction more directly on particulate CHON from biomass burning. Condense the broader discussion of atmospheric organic nitrogen and nitrogen deposition, and bring forward what is known about the effects of fuel composition and combustion conditions on CHON profiles. This would clarify the specific knowledge gap addressed by burning the three biomass components separately.
2. Keywords (lines 31–32). Please streamline the list and spell out the chemical class names where helpful. Consider omitting HR-MS if the keywords are intended to emphasize emission chemistry.
3. Combustion terminology (lines 303–312). Please use combustion for the overall oxygen-containing experiment. Where pyrolysis refers to a thermal-decomposition step within combustion, identify that step explicitly.