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Investigation of Nocturnal Atmospheric Reactivity of Furan Compounds with NO3 Radicals in Simulation Chambers : Kinetics, Products, Mechanisms, and Secondary Organic Aerosol (SOA) Formation.

  • Al Ali, Fatima
Publication Date
Oct 11, 2023
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The study of atmospheric processes is among the central topics of current environmental research. The most direct and significant way to investigate the transformation of pollutants and the formation of aerosols in the atmosphere, is to simulate these processes under controlled and simplified conditions. In this regard, the atmospheric reaction of a series of furan compounds highly emitted from biomass burning (furan (F), 2- methylfuran (2-MF), 3-methylfuran (3-MF), 2,5-dimethylfuran (2,5-DMF), and 2,3,5- trimethylfuran (2,3,5-TMF)) with nitrate radical (NO3) has been in the CHamber for the Atmospheric Reactivity and the Metrology of the Environment (CHARME) simulation chamber at the laboratoire de Physico- Chimie de l’Atmosphere (LPCA) laboratory (Dunkerque, France) and in the Thermally Regulated Atmospheric Simulation Chamber (THALAMOS) at SAGE laboratory- IMT Nord Europe.The first part of this research focused on the determination of the room temperature rate coefficients of the latter reactions with NO3, together with the temperature dependence data of F, 2-MF, 2,5-DMF and two monoterpenes (α-pinene, 2-carene). For the room temperature kinetics, experiments were performed in the dark, under dry conditions (RH <2%), atmospheric pressure and room temperature (294 ± 2 K) using the relative rate method in both simulation chambers (CHARME & THALAMOS). The measurement of the rate coefficients allowed to calculate the atmospheric lifetimes of these furan compounds. The following rate coefficients (in units cm3 molecule−1 s−1) were determined: k(F) = (1.61 ± 0.28) × 10-12, k(2‑MF) = (1.96 ± 0.25) × 10-11, k(3‑MF) = (1.49 ± 0.33) × 10-11, k(2,5‑DMF) = (6.49 ± 0.95) × 10-11 and k(2,3,5‑TMF) = (1.66 ± 0.69) × 10-10. This work shows that the reaction between furan and methylated furan compounds with nitrate radical (NO3) is the dominant removal pathway during the night with lifetimes between 0.5 and 55 min for the studied molecules. The temperature-dependent kinetic studies were studied in THALAMOS in the dark, under dry conditions (RH <2%), atmospheric pressure using relative rate method too. The negative temperature dependence evidenced in the reaction rates of furanoids with NO3 shows that the major reaction pathway is governed by NO3 addition or addition-elimination to the ring.The second part of this research focused on the qualitative and quantitative products determination formed in the gas- and particulate- phase formed from these reactions and the mechanism leading to these oxidation products was proposed. For the five studied furan compounds, the major pathway occurs by NO3 addition to C-2/C-5 of the ring leading to the formation of unsaturated dicarbonyls. For single methylated furan compounds (2-MF and 3-MF), cyclic nitrooxy carbonyls are also formed as major primary product from the NO3 addition to C-2. For multi-methylated furanoids (2,5-DMF and 2,3,5-TMF), another major pathway occurs by NO3 addition followed by H atom-abstraction from one of the methyl groups attached to the furan ring leading to the formation of methyated-furaldehydes as second major products.Comparing the SOA yield obtained from the reaction of 2-MF, 2,5-DMF AND 2,3,5-TMF with NO3, the maximum aerosol yield obtained from the reaction of 2-MF was ≈ 2% which is 5-6 times lower than those obtained from the reaction of 2,5-DMF (≈ 12 %) and 2,3,5-TMF (≈ 10 %). This shows that increasing the methylation on the furan ring increases the SOA yield of formation from the reaction. This is due to the the presence of methyl groups on the ring reducing the volatility or the vapor pressure of a compound.Regarding the composition of the SOA formed from title reaction, it can be concluded that some products identified in the gas-phase where also identified in the particulate phase including the major ones, this shows that these products partition between the gas- and particulate- phase.

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