Recreational gas use spurs nitrous oxide emissions in Ho Chi Minh City
Recreational use of nitrous oxide – commonly known as “laughing gas” – has been identified as a significant and previously overlooked source of greenhouse gas emissions in Ho Chi Minh City, a future Southeast Asian megacity.
Enabled by the first ever on‑the‑ground measurements of nitrous oxide in the city by NCAS scientists, the research sheds new light on how rapidly growing cities contribute to climate change. It also provides a crucial baseline for evaluating Vietnam’s nationwide ban on recreational nitrous oxide introduced in 2025.
Nitrous oxide is warming the planet
Nitrous oxide may be less well known than carbon dioxide as a greenhouse gas, but it is around 300 times more potent at warming the planet and remains in the atmosphere for more than a century. It is also the most important ozone‑depleting substance still being emitted today.
While agriculture is known to be the largest global source of this gas, less is understood about emissions from rapidly expanding urban areas.
Measuring nitrous oxide hotspots in a future megacity
NCAS installed high‑precision monitoring equipment on the roof of a building in central Ho Chi Minh City to continuously measure nitrous oxide levels in the surrounding air between October 2018 and March 2019.
The concentrations of nitrous oxide frequently rose far above what would normally be expected in a city, particularly at night and when winds were blowing from the northeast.
To track down the source, the team carried out additional sampling across the city. This led them to a well‑known nightlife and entertainment area, where nitrous oxide is commonly sold for recreational inhalation using balloons filled from large gas cylinders.
Air samples collected in this area showed extremely high concentrations of nitrous oxide, with an average more than 10 times higher than background levels elsewhere in the city, with the highest sample close to 80 times the background concentration.
Using our observations and a street level survey, we estimated that emissions from recreational use of nitrous oxide in the Bùi Viện Walking Street area could be comparable to those from the city’s entire stationary energy sector, such as emissions from buildings and small industries.
– Dr Grant Forster, NCAS research scientist at the University of East Anglia
Taking action on nitrous oxide emissions
Ho Chi Minh City is expected to become a megacity – with a population exceeding 10 million – within the next decade. Like many large cities, it has committed to ambitious climate targets, including net‑zero emissions by 2050.
This research shows that small‑scale but intense urban activities can have an outsized impact on greenhouse gas emissions and risk being missed in traditional inventories. Understanding where emissions come from is a crucial first step toward reducing them.
Recreational nitrous oxide use is increasing in cities around the world, raising concerns that similar emissions hotspots to Ho Chi Minh City’s may exist elsewhere.
Vietnam introduced a nationwide ban on recreational nitrous oxide in 2025. As our research was carried out before the ban, it provides a valuable baseline to assess the ongoing effectiveness of the new regulation. As cities around the world grow, this research could help policymakers, planners and the public to see the hidden climate impacts of everyday activities, and why tackling climate change requires looking beyond the usual suspects.
– Professor David Oram, NCAS research scientist at the University of East Anglia