Recreational drug-use as an urban source of nitrous oxide

Abstract

N₂O is a potent greenhouse gas which also contributes to depletion of stratospheric ozone. Its primary sources are from natural and agricultural soils and from the ocean. However, other minor sources exist, including industrial processes, combustion processes in the power generation sector and road transport. Very few atmospheric measurements of these minor sources of N₂O exist in the urban environment, particularly in the UK. Nonetheless, they are essential in understanding anthropogenic emissions of N₂O. A custom-built automated sampling system was used to make high-frequency measurements of N₂O, along with SF₆, CO and H₂ at an urban site in the city of Bristol, United Kingdom (UK), from 3rd November 2019 to 26th November 2021. These time-series data provide an insight into urban N₂O mole fractions, diurnal cycles, and possible sources of N₂O during a period of time affected by the COVID-19 pandemic. The data show a pattern of elevated N₂O mole fractions during the late evening and early morning hours on weekends, with no significant correlations with other measured species, indicating the apparent use of N₂O as a recreational drug. The National Atmospheric Emissions Inventory (NAEI) reports UK emissions for recreational N₂O drug use of 12–14 tonnes between 2012 and 2020. We derived a much larger estimate of 89–954 tonnes for the year 2020 using revised estimates of the size of canisters used, the mass of N₂O in each canister and the number of times the drug is used at each sitting.