The Investigation Of Heterogenous Chemical Reaction Of Syringic Acid And Humic Acid With Ozone

Humic-like substances（HULIS）are mainly derived from biomass burning and the secondary generation process.HULIS has significant environmental,climate and healthy effects.Importantly,HULIS can provide heterogeneous reactive sites for gaseous oxides in the atmosphere.Therefore,it is significant to investigate the heterogeneous reaction of HULIS with gaseous oxides for the sources and sinks of atmospheric trace gases.In this study,syringic acid and humic acid were chosen as representative substances of HULIS.The flow tube reactor was used to investigate the influences of various environmental conditions on the heterogeneous uptake of O3 on syringic acid and humic acid.The compositional changes of syringic acid and humic acid by the ozonization were analyzed by the Fourier transform infrared spectrometer（FT-IR）and the gas chromatography-mass spectrometry（GC-MS）.In addition,the changes of optical properties of syringic acid and humic acid by the ozonization were analyzed using ultraviolet-visible（UV-vis）spectrophotometer.The specific results of this study are as follows:During the heterogeneous chemical reaction of syringic acid with O3,the initial uptake coefficient（γi）and 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 the increasing O3 concentration,O2 content and aging time.In addition,the yi was independent of relative humidity（20%-70%）,whereas γss decreased with relative humidity（7%-70%）.The FT-IR results have confirmed that the ozonization caused the changes in the composition and structure of syringic acid,such as the decrease of O-H and C=C groups,the increase of C=O group.The GC-MS results show that the detected one reaction product of ozone with syringic acid was 2,6-dimethoxy1,4-benzoquinone.Compared to that of fresh syringic acid,the absorption and mass absorption efficiency of syringic acid aged by O3 exhibited an increase in the range of 290-320 nm.During the heterogeneous photochemical reaction of humic acid with O3,the γi andγss linearly increased with irradiation intensity(60.7-188.8 W·m^-2),humic acid mass(0-3.18 μg·cm^-2),temperature（278-328 K）and pH（4.0-9.6）,while they decreased with the increasing O3 concentration and O2 content.In addition,the γi was independent of relative humidity（7%-60%）,whereas γss decreased with relative humidity（20%-60%）.The FT-IR results have confirmed that the ozonization caused the changes in the composition and structure of humic acid,such as the decrease of O-H,COOH and C=C groups.Compared to that of fresh humic acid,the absorption and mass absorption efficiency of syringic acid aged by O3 exhibited a decrease in the range of 300-600 nm.