Aqueous brown carbon formation by aldehyde compounds reaction with Glycine/Ammonium sulfate

Brown carbon (BrC) can absorb solar radiation in the ultraviolet (UV) and near visible (Vis) regions, which plays an important role in the Earth's radiative balance and global climate. 1,4-dioxane-2,5-diol (DD), glyoxal (GX) and acetaldehyde (AAld) appeared moderate absorbent and fluorescent, when each of them reaction with glycine (Gly)/ammonium sulfate (AS). Combined with the previous experimental studies of the methylglyoxal (MG), GX reaction with GX/AS, novelty conclusions are as following: the absorbance of the reaction products in the same reaction time followed the order: MG-Gly＞DD-Gly＞GX-Gly＞AAld-Gly, DD-AS＞MG-AS＞GX-AS＞AAld-AS. And for the same aldehyde compound reaction with Gly the reaction rate was faster than with AS. Three-dimensional excitation-emission matrix (EEM) plot showed that, with the increasing of reaction time, red shift of emission peak occurred in MG-Gly/AS and GX-Gly, no shift occurred in DD-Gly/AS and AAld-Gly, and blue shift occurred in GX-AS. The H₂O₂ oxidation photolysis results showed that the effective H₂O₂ oxidation photolysis rate constants (k) in the visible region are larger than in UV region for the reaction MG, GX, DD with Gly. But for AAld-Gly system, the k in the visible region is smaller than in the UV region. Besides, the reaction MG, GX, DD, AAld with Gly clearly showed that the presence of abundant organic products by Liquid chromatography/mass spectrometry (LC/MS) analysis.