Heterogeneous oxidation of SO2 by O3-aged black carbon and its dithiothreitol oxidative potential

Ozone (O3) is an important atmospheric oxidant. Black carbon (BC) particles released into the atmosphere undergo an aging process via O3 oxidation. O3-aged BC particles may change their uptake ability toward trace reducing gases such as SO2 in the atmosphere, leading to different environmental and health effects. In this paper, the heterogeneous reaction process between O3-aged BC and SO2 was explored via in-situ diffuse reflectance infrared Fourier transform spectroscopy (DRIFTS). Combined with ion chromatography (IC), DRIFTS was used to qualitatively and quantitatively analyze the sulfate product. The results showed that O3-aged BC had stronger SO2 oxidation ability than fresh BC, and the reactive species/sites generated on the surface had an important role in the oxidation of SO2. Relative humidity or 254 nm UV (ultraviolet) light illumination enhanced the oxidation uptake of SO2 on O3-aged BC. The oxidation potentials of the BC particles were detected via dithiothreitol (DTT) assay. The DTT activity over BC was decreased in the process of SO2 reduction, with the consumption of oxidative active sites.

Graphical abstractChanges of DTT activity and sulfate production of ozonized UBC particles in the reaction with SO2: sulfate formation was negatively correlated with DTT activity as a function of exposure time of ozonized UBC to SO2, which is due to the consumption of the active sites on the surface of the particles during the reaction.Figure optionsDownload full-size imageDownload as PowerPoint slide