# Evaluation of the SOA Formation in the Reaction of Furfural with Atmospheric Oxidants
## 3 Results and Discussion
### Gas-Phase Products
In GC-TOFMS experiments, similar results were obtained as in the case of the reaction with chlorine atoms in the presence of NOx. Three products were identified by gas chromatography after 3.5 h of reaction: maleic anhydride, 2-nitrofuran and 2-furylnitroketone (not confirmed). For FTIR experiments, after 60 min of reaction, the typical IR bands of -ONO\({}_{2}\) (852, 1288 and 1666 cm\({}^{-1}\)) and -OONO\({}_{2}\) (792, 1030 and 1726 cm\({}^{-1}\)) groups were observed (Figure S4, Supplementary Materials). Once again, the band at 1805 cm\({}^{-1}\) can be assigned to the presence of a substituted lactone (in this case 5-hydroxy-2(5\(H\))-furanone (P6), maleic anhydride (P2), or 5-nitrate-2-(5\(H\))-furanone (P1)). The band at 1840 cm\({}^{-1}\) may be due to the presence of another C=O group of a nitrate compound, which could be assigned to the formation of 2-furyllectone mentioned above. The formation of 5-nitrate-2-(5\(H\))-furanone and maleic anhydride have also been suggested in the literature [9]. The IR absorption bands observed are also consistent with the formation of 5-hydroxy-2-(5\(H\))-furanone and 3-nitrate-2-hydroperoxy-3(2\(H\))-furanone, which were theoretically proposed in work by [PERSON] et al. [9]. Once again, the presence of these products was not confirmed because they are not commercially available. Figure 2: Gas chromatograms obtained for the reaction of furfural with chlorine atoms in the presence of NO at different times: t = 0 min (**a**), t = 5 min (**b**) and t = 10 min (**c**). The quantification of the identified products was only possible in certain cases. The product concentrations were estimated using calibration curves obtained previously by introducing into the reactor a set of samples of known concentration. For some products, such as 5-chloro-2(5\(H\))-furanone and NO\({}_{2}\), the concentration profiles were obtained using IR absorption cross-sections found in the literature [19]. In the case of 5-chloro-2-(5\(H\))-furanone, the concentration was estimated using the IR absorption coefficient of the 2-(5\(H\))-furanone [19] because of their structural similarity and since the former is not commercially available. A value for this coefficient of \((1.65\pm 0.27)\times 10^{-3}\) ppm V\({}^{-1}\) m\({}^{-1}\) for the band of 1811 cm\({}^{-1}\) was used. For NO\({}_{2}\), a value of \((1.46\pm 0.04)\times 10^{-3}\) ppm V\({}^{-1}\) m\({}^{-1}\) for the band at 1630 cm\({}^{-1}\) was taken for the quantitative analysis. In addition to these two products, the concentrations of maleic anhydride, CO, HCl, HNO\({}_{3}\) and 2-nitrofuran were obtained. An example of the concentration-time profiles for the reaction of Cl atoms and furfural is shown in Figure 3.  
The profiles are typical of primary products that undergo a progressive increase in the concentration from the early stages of the reaction. Similar time-concentration profiles were obtained for 5-chloro-2-(5\(H\))-furanone, CO and HCl in the case of the reaction of furfural with chlorine atoms in the presence of NOx. In the cases of maleic anhydride and 2-nitrofuran, the curves obtained after 4-6 min of reaction and using GC-MS/TOF suggest the loss of these products through secondary reactions (Figure S5, Supplementary Materials). As mentioned before, chloroformane has a typical primary product profile while the nitro-2-furylketone (P7) has a secondary product profile (Figure S6, Supplementary Materials). This may indicate that high levels of NO\({}_{2}\) are required for the generation of this product (P7). The yields of the primary products were obtained from the slopes of plots of the amounts of reaction product formed versus the amounts of consumed furfural. The product yields obtained for the reaction of furfural with different oxidants are provided in Table 1.  
Figure 3: FTIR concentration–time profiles for the reaction of furfural with chlorine atoms. \(\blacklozenge\) Furfural, \(\blacksquare\) HCl, \(\bullet\) CO, \(\blacklozenge\) 5-chloro-2-(5\(H\))-furanone.