Measurements of methane and nitrous oxide in human breath and the development of UK scale emissions

PLoS One. 2023 Dec 13;18(12):e0295157. doi: 10.1371/journal.pone.0295157. eCollection 2023.


Exhaled human breath can contain small, elevated concentrations of methane (CH4) and nitrous oxide (N2O), both of which contribute to global warming. These emissions from humans are not well understood and are rarely quantified in global greenhouse gas inventories. This study investigated emissions of CH4 and N2O in human breath from 104 volunteers in the UK population, to better understand what drives these emissions and to quantify national-scale estimates. A total of 328 breath samples were collected, and age, sex, dietary preference, and smoking habits were recorded for every participant. The percentage of methane producers (MPs) identified in this study was 31%. The percentage of MPs was higher in older age groups with 25% of people under the age of 30 classified as MPs compared to 40% in the 30+ age group. Females (38%) were more likely to be MPs than males (25%), though overall concentrations emitted from both MP groups were similar. All participants were found to emit N2O in breath, though none of the factors investigated explained the differences in emissions. Dietary preference was not found to affect CH4 or N2O emissions from breath in this study. We estimate a total emission of 1.04 (0.86-1.40) Gg of CH4 and 0.069 (0.066-0.072) Gg of N2O in human breath annually in the UK, the equivalent of 53.9 (47.8-60.0) Gg of CO2. In terms of magnitude, these values are approximately 0.05% and 0.1% of the total emissions of CH4 and N2O reported in the UK national greenhouse gas inventories.

MeSH terms

  • Aged
  • Carbon Dioxide / analysis
  • Greenhouse Gases* / analysis
  • Humans
  • Methane / analysis
  • Nitrous Oxide / analysis
  • United Kingdom


  • Greenhouse Gases
  • Nitrous Oxide
  • Methane
  • Carbon Dioxide

Grants and funding

The analysis was funded by the UK NERC grant E/S003614/2 ‘Detection and Attribution of Regional greenhouse gas Emissions in the UK (DAREUK)’. We acknowledge contribution from UKSCAPE Programme, funded by the Natural Environment Research Council as National Capability (award number NE/R016429/1). The funders had no role in study design, data collection and analysis, decision to publish, or preparation of the manuscript.