Heterogeneous Reactions of Particulate Methoxyphenols with NO3 Radicals: Kinetics, Products, and Mechanisms

• Published in: Environmental science & technology Vol. 46; no. 24; pp. 13262 - 13269
• Main Authors: Liu, Changgeng, Zhang, Peng, Wang, Youfeng, Yang, Bo, Shu, Jinian
• Format: Journal Article
• Language: English
• Published: Washington, DC American Chemical Society 18.12.2012
• Subjects: Acrolein - analogs & derivatives; Acrolein - chemistry; aerosols; Applied sciences; Atmosphere - chemistry; Atmospheric pollution; Benzaldehydes - chemistry; chemical degradation; Combustion and energy production; Exact sciences and technology; free radicals; gas chromatography-mass spectrometry; gases; isoprene; Kinetics; Mass Spectrometry; Nitrates - chemistry; oxalic acid; Particulate Matter - chemistry; Pollution; Pollution sources. Measurement results; protocatechuic acid; reaction mechanisms; smoke; spectrometers; tracer techniques; vanillic acid; Vanillic Acid - chemistry; vanillin; Combustion residue; Wood; Ether; Pollutant behavior; Reaction product; Combustion; Nitrates; Biomass; Oxidant; Aldehyde; Free radical reaction; Chemical reaction kinetics; Carboxylic acid; Aerosols; Reaction mechanism; Phenols; Air pollution; Organic compounds; Inorganic radical anion; Heterogeneous reaction; Tracers
• ISSN: 0013-936X; 1520-5851; 1520-5851
• DOI: 10.1021/es303889z

Methoxyphenols, tracers for wood smoke, are emitted into the atmosphere in large quantities, but their chemical degradation in the atmosphere has not been well characterized. In this study, heterogeneous kinetics of particulate syringaldehyde (SA), vanillic acid (VA), and coniferyl aldehyde (CA) with NO3 radicals is investigated with a mixed-phase relative rate method. A vacuum ultraviolet photoionization aerosol time-of-flight mass spectrometer and an atmospheric gas analysis mass spectrometer are used to monitor online the decays of particulate methoxyphenols and gas-phase isoprene synchronously. The reactive uptake coefficients of NO3 radicals on SA, VA, and CA particles are calculated to be 0.33, 0.31, and 0.28, respectively, according to the measured methoxyphenol loss ratios and the average NO3 concentrations. The effective rate constants for heterogeneous reactions of particulate SA, VA, and CA with NO3 radicals measured under experimental conditions are 5.7 × 10–12, 5.2 × 10–12, and 3.5 × 10–12 cm3 molecule–1 s–1, respectively. In addition, oxalic acid, 2,6-dimethoxybenzoquinone, 5-nitro-VA, 4,6-dinitrogaiacol, protocatechuic acid, vanillin, 5-nitrovanillin, VA, and 5-nitro-CA are identified as the reaction products by gas chromatography–mass spectrometry analysis. On the basis of the identified products, the reaction mechanisms of methoxyphenols with NO3 radicals are proposed. The main transformation pathway of methoxyphenols is the NO3 electrophilic addition, followed by H-abstraction and nitro-substituted processes. The experimental results might shed light on the chemical behaviors of methoxyphenols at night.