Rate constant and secondary organic aerosol yields for the gas-phase reaction of hydroxyl radicals with syringol (2,6-dimethoxyphenol)

Abstract

Syringol (2,6-dimethoxyphenol) is a potential marker compound for wood smoke emissions in the atmosphere. To investigate the atmospheric reactivity of this compound, the rate constant for its reaction with hydroxyl radicals (OH) has been determined in a simulation chamber (8 m3) at 294 ± 2 K, atmospheric pressure and low relative humidity (2–4%) using the relative rate method. The syringol and reference compound concentrations were followed by GC/FID (Gas chromatography/Flame Ionization Detection). The determined rate constant (in units of cm3 molecule−1 s−1) is ksyringol = (9.66 ± 1.11) × 10−11. The calculated atmospheric lifetime for syringol is 1.8 h, indicating that it is too reactive to be used as a tracer for wood smoke emissions. Secondary Organic Aerosol (SOA) formation from the OH reaction with syringol was also investigated. The initial mixing ratios for syringol were in the range 495–3557 μg m−3. The aerosol production was monitored using a SMPS (Scanning Mobility Particle Sizer). The SOA yields (Y) were determined as the ratio of the suspended aerosol mass corrected for wall losses (M0) to the total reacted syringol concentration assuming a particle density of 1.4 g cm−3. The aerosol formation yield increases as the initial syringol concentration increases, and leads to aerosol yields ranging from 0.10 to 0.36. Y is a strong function of M0 and the organic aerosol formation can be expressed by a one-product gas/particle partitioning absorption model. To our knowledge, this work represents the first investigation of the rate constant and SOA formation for the reaction of syringol with OH radicals. The atmospheric implications of this reaction are also discussed.