# Evaluation of the SOA Formation in the Reaction of Furfural with Atmospheric Oxidants
## 3 Results and Discussion
### SOA Size Distributions  
The few products identified in the gas-phase study and their low yields lead us to believe that some of the reaction products generated are not being observed in the gas-phase. This may be because many of the furfural reaction products are in a condensed phase, and therefore, they are not being correctly sampled. For this purpose, a series of experiments was performed under atmospheric pressure and room temperature (similar experimental conditions to those used in the products' experiments) to study the formation of aerosols in the reaction of furfural with Cl, OH and O3. The same set of experiments was performed to study the reaction with NO3, but particle formation was not observed. The decay of furfural versus the variation of SOA mass (M0) for the reaction with chlorine atoms is represented in Figure 4. The steady state for aerosol production was observed after 30 min, with a maximum mass of around \(9\times 10^{2}\)\(\mu\)g m\({}^{-3}\) for the reaction with chlorine atoms. A typical concentration profile, as described in the literature [21], was observed in this experiment, thus suggesting a strong relationship between the concentration of furfural and aerosol generation. As SOA wall loss was observed, the aerosol mass concentration (M0) was corrected by using the wall deposition coefficient rate obtained in this work (\(kw=(2.95\pm 0.46)\times 10^{-5}\) s\({}^{-1}\)). A significant amount of particulate matter, i.e., between 60 and 950 \(\mu\)g m\({}^{-3}\), was observed in the oxidation of furfural with chlorine atoms, OH radicals and ozone at the stationary state. This state is rapidly reached after 30 min for the chlorine and ozone reactions and after 5 min for the OH reaction. The furfural concentration was monitored by offline SPME sampling and analyzed by GC-TOFMS. The fiber was exposed in the reactor during 60 s and then thermally desorbed during 15 min at 250 \({}^{\circ}\)C in the injection port of the gas chromatograph. The reactor was filled with purified air, a quantity of reactant (2.5-3.5 \(\mu\)g m\({}^{-3}\)) and oxidant (\(\sim\)2.5 \(\times\) 10\({}^{14}\) molecule cm\({}^{-3}\)). For the study with chlorine atoms and OH radicals, six visible lamps were employed to start the reaction. Ozone was obtained from an ozonizer as mentioned above. Prior tests were performed to confirm the absence of particle generation from the exposure of furfural to light. Figure 4: Profile of furfural and aerosol mass under chlorine degradation conditions. All of the experiments were carried out in the absence of inorganic seed aerosol. The initial concentrations employed for the oxidant ([Ox. ]0) and furfural or reactive organic gas ([ROG]0) are listed in Table 2 together with the reacted furfural (\(\Delta\)[ROG]) and aerosol yield, Y. The overall organic aerosol yield was determined by employing Equation (1):  
\[\mathrm{Y}=\frac{\mathrm{M}_{0}}{\Delta[\mathrm{ROG}]} \tag{1}\]  
where \(\mathrm{M}_{0}\) is the organic aerosol mass concentration and \(\Delta\)[ROG] is the reacted furfural, both in \(\mathrm{\SIUnitSymbolMicro g}\) m\({}^{-3}\). It can be seen from the results that atmospheric degradation of furfural leads to the formation of low vapor pressure products (particulate matter), as previously proposed in the gas-phase study. The yield of the reaction with chlorine atoms is between 6 to 10 times greater than in the cases of ozone and OH. The particle size obtained is also larger for the reaction with chlorine (diameters 107-523 nm) and this suggests that the reaction of furfural with this oxidant leads to a more effective formation of aerosols. In the reaction of furfural with the OH radical, particles were formed by irradiation of the precursor mixture (CH3 ONO and NO) with visible lamps in air. The concentration and particle size observed under the same experimental conditions were lower than those obtained in the reaction with chlorine atoms.