Rapid increase in atmospheric glyoxal and methylglyoxal concentrations in Lhasa, Tibetan Plateau: Potential sources and implications

Glyoxal (Gly) and methylglyoxal (Mgly) are the intermediate products of several volatile organic compounds (VOCs) as well as the precursors of brown carbon and may play key roles in photochemical pollution and regional climate change in the Tibetan Plateau (TP). However, their sources and atmospheric behaviors in the TP remain unclear. During the second Tibetan Plateau Scientific Expedition and Research in the summer of 2020, the concentrations of Gly (0.40 ± 0.30 ppbv) and Mgly (0.57 ± 0.16 ppbv) observed in Lhasa, the most densely populated city in the TP, had increased by 20 and 15 times, respectively, compared to those measured a decade previously. Owing to the strong solar radiation, secondary formations are the dominant sources of both Gly (71%) and Mgly (62%) in Lhasa. In addition, primary anthropogenic sources also play important roles by emitting Gly and Mgly directly and providing abundant precursors (e.g., aromatics). During ozone pollution episodes, local anthropogenic sources (industries, vehicles, solvent usage, and combustion activities) contributed up to 41% and 45% in Gly and Mgly levels, respectively. During non-episode periods, anthropogenic emissions originating from the south of Himalayas also have non-negligible contributions. Our results suggest that in the previous decade, anthropogenic emissions have elevated the levels of Gly and Mgly in the TP dramatically. This study has important implications for understanding the impact of human activities on air quality and climate change in this ecologically fragile area.