Heterogeneous reaction of ozone with syringic acid: Uptake of O3 and changes in the composition and optical property of syringic acid

Abstract

Syringic acid, which is a typical methoxyphenol emitted from wood combustion, can provide heterogeneous reaction sites for gaseous active components, influencing the concentrations of trace gases and the compositions of syringic acid. The heterogeneous uptake of O3 on syringic acid was investigated using a flow tube reactor under ambient pressure. The initial uptake coefficient (γi) and the steady-state uptake coefficient (γss) of O3 linearly increased with syringic acid mass (0–0.16 μg cm−2) and temperature (278–328 K), while they decreased with increasing the O3 concentration and the O2 content. The γi was independent of relative humidity (20%–70%), whereas γss decreased with relative humidity (7%–70%). The compositional changes of syringic acid by the ozonization were analyzed by the Fourier transform infrared spectrometer (FT-IR) and the gas chromatography-mass spectrometry (GC-MS), confirming the generation of 2,6-dimethoxy-1,4-benzoquinone. In addition, compared to that of fresh syringic acid, the mass absorption efficiency of syringic acid aged by O3 exhibited an increase in the range of 290–320 nm.