Secondary organic aerosol formation from the gas-phase reaction of guaiacol (2-methoxyphenol) with NO_3 radicals

摘要

Methoxyphenols are oxygenated aromatic compounds emitted by wood combustion (consequently to the pyrolysis of lignin). The atmospheric reaction of nitrate radical (NO3) with guaiacol (2-methoxyphenol), one of the principal representatives of this class of compounds has been investigated in the dark at (294 +/- 2) K, atmospheric pressure and low relative humidity (RH 2%). The formation of secondary organic aerosols (SOAs) has been studied in two simulation chambers. The concentrations time profiles of guaiacol were followed with a PTR-ToF-MS (Proton Transfer Mass Reaction - Time of Flight - Mass Spectrometer) and those of SOAs by an SMPS (Scanning Mobility Particle Sizer). Aerosol yields (Y) were calculated from the ratio of the suspended aerosol mass concentration corrected for wall losses (M-0), to the total reacted guaiacol concentration assuming a particle density of 1.4 g cm(-3). The aerosol yield increases as the initial guaiacol concentration rises, leading to yield values ranging from 0.01 to 0.21. A very good agreement was observed between the experiments performed in both chambers which gives confidence in the data obtained in this study. The organic aerosol formation can be represented by a one-product gas/particle partitioning absorption model with a stoichiometric coefficient alpha = 0.32 +/- 0.04 and an equilibrium constant K = (4.2 +/- 1.0) x 10(-3) m(3) mu g(-1). The chemical composition of the aerosols formed was studied after sampling on quartz fiber filter, ultrasonic extraction and analysis by ESI-LC-QToF-MS-MS (ElectroSpray Ionization - Liquid Chromatography - Quadrupole - Time of Flight - Tandem Mass Spectrometry). The oxidation products observed in the condensed phase are mostly nitro-aromatics; they display chemical structures with one, two and three aromatic rings. A reaction mechanism leading to these products has been proposed. To our knowledge, this work represents the first study on the SOAs formation from the reaction of guaiacol with NO3 radicals.