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# Furans Formation and Atmospheric Implications

Philippe Dagaut

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Philippe Dagaut. Furans Formation and Atmospheric Implications. Twenty-Second International Conference on Flow Dynamics, IFS, Tohoku University, Nov 2025, Sendai, Japan. hal-05368777

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Submitted on 17 Nov 2025

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TOHOKU
UNIVERSITY

Proceedings

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22nd International Conference on Flow Dynamics

Nov. 10-13, 2025

Sendai International Center,
Sendai, Miyagi, Japan

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Institute of Fluid Science, Tohoku University
# Furans Formation and Atmospheric Implications

Philippe Dagaut¹

¹CNRS, ICARE

1C Avenue de la recherche scientifique, Orleans, 45071, France

## ABSTRACT

Whereas the formation of furans has been reported in biomass fires, less is known about their formation during hydrocarbon oxidation. Here, we present results obtained during the oxidation of hydrocarbons ranging from C4 to C10. The experiments were conducted in a jet-stirred reactor under dilute conditions. We analyzed the reacting mixtures using gas chromatography with FID/MS detection and FTIR. We demonstrate that furans form over a temperature range of approximately 550 to 900 K and present their formation mechanisms and atmospheric implications.

## 1. Introduction

Furanoids, also simply called furans, are a class of reactive volatile organic compounds that are major products from the pyrolysis and combustion of biomass polymers, including cellulose, hemicellulose, and lignin. It has been observed that biomass burning has the potential to be a significant source of furanoids, with a rising trend in both frequency and intensity being noted across various regions worldwide [1,2]. Furanoids are a chemical class of heterocyclic organic molecules that have been found to be present in trace amounts in the atmosphere. Furanoids are broadly defined as an organic molecule containing a five-membered ring with four carbon atoms and one oxygen atom. A furanoid can be aromatic, partially saturated, or fully saturated. It has been observed that such chemicals are present during the cool flame oxidation of hydrocarbons [3,4]. In an effort to understand this phenomenon, some chemical kinetic models have been proposed to simulate their formation [5]. However, it seems that there might be a missing piece to this puzzle. This issue is addressed in this study.

## 2. Method

The experiments were conducted in a 42-mL fused silica jet-stirred reactor (JSR). The fuel samples, which were 99% pure or higher, were injected using an HPLC pump with an online degasser. The fuels were subsequently delivered to a vaporizer assembly with an N₂ flow. Prior to entering the JSR, the fuel and oxygen flows were separated to prevent premature fuel oxidation. The nitrogen and oxygen flow rates were regulated by mass flowmeters. The thermal homogeneity of the reactor was checked by utilizing a silica-protected thermocouple (0.1 mm). The oxidation of n-butane, n-pentane, n-hexane, n-heptane, a 50:50 n-heptane-iso-octane (RON 50), n-octane, n-propylcyclohexane, and n-decane was studied, with initial fuel mole fractions ranging from 0.1 to 0.4% and residence times ranging from 0.5 to 1.4 seconds. The operating conditions were: 10 bar, 500-1200 K, and fuel-lean to fuel-rich (φ = 0.25-1.5).

Samples of the reacting mixtures were collected in Pyrex bulbs using a sonic fused-silica probe. Gas chromatography (GC) analyses were performed. GC-TCD, GC-FID, and GC-MS were used for quantification and identification. Online FTIR quantification was also performed to measure H₂O, CH₂O, CO, and CO₂.

## 3. Results and Discussion

Besides simple oxidation products, oxygen, and fuels, furans were measured. Table 1 gives a summary of the results.

<table><caption>Table 1 Summary of furans detection in a JSR (φ = 1).</caption><thead><tr><th>Fuels</th><th>Furans</th><th>Relative amount</th></tr></thead><tbody><tr><td>n-butane</td><td>Tetrahydrofuran (THF)</td><td>1.0</td></tr><tr><td rowspan="2">n-pentane</td><td>2-Me-furan</td><td>0.02</td></tr><tr><td>2-Me-THF</td><td>1.0</td></tr><tr><td rowspan="3">n-hexane</td><td>2,5-di-Me THF trans</td><td>0.7</td></tr><tr><td>2,5-di-Me THF cis</td><td>1.0</td></tr><tr><td>2-Et-THF</td><td>0.6</td></tr><tr><td rowspan="3">n-heptane</td><td>2-Me-5-Et-THF trans</td><td>0.8</td></tr><tr><td>2-Me-5-Et-THF cis</td><td>1.0</td></tr><tr><td>2-Pr-THF</td><td>0.4</td></tr><tr><td rowspan="4">RON 50</td><td>2-Me-5-Et-THF trans</td><td>0.5</td></tr><tr><td>2-Me-5-Et-THF cis</td><td>0.7</td></tr><tr><td>2,2,4-tetra-Me-THF</td><td>1.0</td></tr><tr><td>2-Pr-THF</td><td>0.2</td></tr><tr><td rowspan="2">n-octane</td><td>2,5-di-Me-THF trans</td><td>0.4</td></tr><tr><td>2,5-di-Me-THF cis</td><td>1.0</td></tr><tr><td rowspan="6">n-propyl cyclohexane</td><td>Furan</td><td>1.0</td></tr><tr><td>THF</td><td>0.4</td></tr><tr><td>2-Me-furan</td><td>0.2</td></tr><tr><td>2-Et-furan</td><td>0.1</td></tr><tr><td>2-Pr-furan</td><td>0.3</td></tr><tr><td>Dihydrofuran</td><td>0.2</td></tr><tr><td rowspan="6">n-decane</td><td>2,5-di-Pr-THF cis</td><td>0.8</td></tr><tr><td>2,5-di-Pr-THF trans</td><td>0.3</td></tr><tr><td>2-Et-5-Bu-THF cis</td><td>0.8</td></tr><tr><td>2-Et-5-Bu-THF trans</td><td>0.4</td></tr><tr><td>5-Me-5-Pe-THF cis</td><td>1.0</td></tr><tr><td>5-Me-5-Pe-THF trans</td><td>0.5</td></tr></tbody></table>

It was observed that these products are produced over the temperature range 550 to 900 K. Cis- and trans-
isomers were observed. Under the present experimental conditions, one could observe 2-stage formation of these products, as depicted in Figures 1 and 2. Whereas Figure 1 shows only the data for 2-methyl-THF, Figure 2 present the data obtained for six substituted TFH isomers. Although these products are not of major importance in terms of mole fraction, they are not negligible. Their formation pathways involve the initial formation of a peroxy radical (ROO) which can isomerize via H-atom transfer yielding an organic hydroperoxyl radical (QOOH).

<figure><img src="image_6.png" /><figcaption>Fig. 1 Mole fractions of 2-methyl-furan measured in a JSR at 10 bar (1000 ppm of n-pentane, φ=1).</figcaption></figure>

<figure><img src="image_7.png" /><figcaption>Fig. 2 Mole fractions of furans measured in a JSR at 10 bar (1000 ppm of n-decane, φ=1): 2,5-di-Pr-THF cis (25DPRC), 2,5-di-Pr-THF trans (25DPRT), 2-Et-5-Bu-THF cis (25ETBUC), 2-Et-5-Bu-THF trans (25ETBUT), 5-Me-5-Pe-THF cis (25MEPEC), and 5-Me-5-Pe-THF trans (25MEPET).</figcaption></figure>

These organic hydroperoxyl radicals can decompose yielding a cyclic ether and a hydroxy radical. The 2-stage formation of these cyclic ethers results from the negative temperature coefficient (NTC) behavior. The formation of cyclic ethers declines under NTC conditions. At higher temperature > 700 K, the rate of formation of cyclic ethers increases due to the production of OH radicals via hydrogen peroxide decomposition followed by a second formation of ROO which can produce cyclic ethers via

isomerization and decomposition. Therefore, besides biomass burning, the combustion of fuels can contribute to the emission of furans. Furans emitted by biomass burning come from pyrolysis of biopolymers and combustion of pyrolysis products.

Once emitted, furans are expected to react in the troposphere, producing ozone, secondary organic aerosols (SOA), and other secondary products. Unlike other important atmospheric constituents, e.g., nonheterocyclic aromatics, oxygenates, and biogenic volatile organic compounds (VOCs), the atmospheric chemistry of furans has only been thoroughly reviewed recently [7]. Furans in the troposphere, react with the major tropospheric oxidants, i.e., hydroxy radicals, nitrate radicals (NO₃), ozone, and chlorine atoms. These reactions lead to the formation of secondary pollutants that alter atmospheric composition.

## 4. Concluding Remarks

We oxidized hydrocarbons ranging from C4 to C10 in a jet-stirred reactor at 10 bar under dilute conditions. The oxidation products were analyzed using FTIR and gas chromatography with FID/MS detection. The results of this study show that furans are produced over a temperature range of 550 to 900 K and that their two-stage formation results from complex oxidation pathways. The formation of these combustion-generated pollutants adds to biomass burning, a major source of VOCs in the troposphere.

## References

[1] S. K. Akagi, R. J. Yokelson, C. Wiedinmyer, M. J. Alvarado, J. S. Reid, T. Karl, J. D. Crounse, P. O. Wennberg, *Atmos. Chem. Phys.*, **11**, (2011), 4039–4072.

[2] M. O. Andreae, *Atmos. Chem. Phys.*, **19**, (2019), 8523–8546.

[3] P. Dagaut, M. Reuillon, and M. Cathonnet, *Combust. Sci. and Tech.*, **103**, (1994), 349–359.

[4] P. Dagaut, M. Reuillon, M. Cathonnet, and D. Presvots, *Chromatographia*, **40**, (1995), 147–154.

[5] J. Bugler, A. Rodriguez, O. Herbinet, F. Battin-Leclerc, P. Dagaut, H. J. Curran, *Proc. Combust. Inst.*, **36**, (2017), 441–448.

[6] P. Dagaut, M. Cathonnet, J.P. Rouan, R. Foulatier, A. Quilgars, J.C. Boettner, F. Gaillard and H. James, *J. Physics E: Instrum.*, **19**, (1986), 207–209.

[7] M.N. Romanias, M.M. Coggon, F. Al Ali, J.B. Burkholder, P. Dagaut, C. Warneke, C.E. Stockwell, Z. Decker, A. Tomas, N. Houzel, C. Coeur, S.S. Brown, *Earth and Space Chemistry*, **8**, (2024), 857–899.

## Acknowledgements

This work received financial support from the LabEx CAPRYSSES (ANR-11-LABX-006-01) and from the European Research Council under the European Community's 7th Framework Programme (FP7/2007-2013) / ERC grant agreement no. 291049 2G-CSafe.