Declining oxygen level as an emerging concern to global cities

Jianping Huang, Yun Wei, Jianguo Wu, Xiaoyue Liu, Dongliang Han, Linli An, Haipeng Yu, Jiping Huang

Research output: Contribution to journalArticlepeer-review

15 Scopus citations


Rising CO2 concentration and temperatures in urban areas are now well-known, but the potential of an emerging oxygen crisis in the world's large cities has so far attracted little attention from the science community. Here, we investigated the oxygen balance and its related risks in 391 global large cities (with a population of more than 1 million people) using the oxygen index (OI), which is the ratio of oxygen consumption to oxygen production. Our results show that the global urban areas, occupying only 3.8% of the global land surface, accounted for 39% (14.3 ± 1.5 Gt/yr) of the global terrestrial oxygen consumption during 2001−2015. We estimated that 75% of cities with a population more than 5 million had an OI of greater than 100. Also, cities with larger OI values were correlated with more frequent heatwaves and severe water withdrawals. In addition, cities with excessively large OI values would likely experience severe hypoxia in extremely calm weather. Thus, mitigation measures should be adopted to reduce the urban OI in order to build healthier and more sustainable cities.

Original languageEnglish (US)
Pages (from-to)7808-7817
Number of pages10
JournalEnvironmental Science and Technology
Issue number12
StatePublished - Jun 15 2021


  • Heatwave
  • Hypoxia
  • Large cities
  • Oxygen index
  • Water shortages

ASJC Scopus subject areas

  • Chemistry(all)
  • Environmental Chemistry


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