Declining Oxygen Level as an Emerging Concern to Global Cities

A comprehensive review of natural products with anti-hypoxic activity

Natural products exhibit substantial impacts in the field of anti-hypoxic traetment. Hypoxia can cause altitude sickness and other negative effect on the body. Headache, coma, exhaustion, vomiting and, in severe cases, death are some of the clinical signs. Currently, hypoxia is no longer just a concern in plateau regions; it is also one of the issues that can not be ignored by urban residents. This review covered polysaccharides, alkaloids, saponins, flavonoids, peptides and traditional Chinese compound prescriptions as natural products to protect against hypoxia. The active ingredients, effectiveness and mechanisms were discussed. The related anti-hypoxic mechanisms involve increasing the hemoglobin (HB) content, glycogen content and adenosine triphosphate (ATP) content, removing excessive reactive oxygen species (ROS), reducing lipid peroxidation, regulating the levels of related enzymes in cells, protecting the structural and functional integrity of the mitochondria and regulating the expression of apoptosis-related genes. These comprehensive summaries are beneficial to anti-hypoxic research and provide useful information for the development of anti-hypoxic products.

"Urban Respiration" Revealed by Atmospheric O2 Measurements in an Industrial Metropolis

Urban regions, which "inhale" O₂ from the air and "exhale" CO₂ and atmospheric pollutants, including harmful gases and fine particles, are the largest sinks of atmospheric O₂, yet long-term O₂ measurements in urban regions are currently lacking. In this study, we report continuous measurements of atmospheric O₂ in downtown Lanzhou, an industrial metropolis in northwestern China. We found declines in atmospheric O₂ associated with deteriorated air quality and robust anticorrelations between O₂ and gaseous oxides. By combining O₂ and pollutants measurements with a Lagrangian atmospheric transport model, we quantitatively break down "urban respiration" (ΔO_2URB) into human respiration (ΔO_2RES) and fossil fuel combustion (ΔO_2FF). We found increased ΔO_2FF contribution (from 66.92% to 72.50%) and decreased ΔO_2RES contribution (from 33.08 to 27.50%) as O₂ declines and pollutants accumulate. Further attribution of ΔO_2FF reveals intracity transport of atmospheric pollutants from industrial sectors and suggests transportation sectors as the major O₂ sink in downtown Lanzhou. The varying relationships between O₂ and pollutants under different conditions unfold the dynamics of urban respiration and provide insights into the O₂ and energy consumption, pollutant emission, and intracity atmospheric transport processes.

The evolution of ecological security and its drivers in the Yellow River Basin

Ecological security is the state achieved once an ecosystem maintains its stability under external stress. The Yellow River Basin (YRB) is the largest river basin in northwest and north China and an important area for grain and energy production. The assessment and attribution of ecological security in the YRB are important for protecting the natural environment and ensuring sustainable development. Here, the ecological security of the YRB was assessed by the ecological security index (ESI), a comprehensive index based on the oxygen cycle, and its drivers were attributed to climate change, human activities, vegetation, and soil factors. The spatial pattern of ecological security in the YRB showed high heterogeneity. Ecological insecurity occurred mainly in the middle reaches and regions where the major stream of the Yellow River passes through. The ESI decreased at a rate of - 0.82/year since 2000, which indicated the natural environment continued to be improved in the YRB. Climate change dominated the evolution of ecological security in the upper reaches. The level of ecological security has been improved in the middle reaches after a series of ecological restoration projects conducted. With higher intensity of industrial activity, human activities played a more critical role in ecological security in the lower reaches. Our results suggested that government and local people need to adopt different strategies and actions based on the dominant drivers in the upper, middle, and lower reaches to ensure protection of the natural environment and achieve sustainable development targets.