Recreational drug-use as an urban source of nitrous oxide

N 2 O 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 N 2 O exist in the urban environment, particularly in the UK. Nonetheless, they are essential in understanding anthropogenic emissions of N 2 O. A custom-built automated sampling system was used to make high-frequency measurements of N 2 O, along with SF 6 , CO and H 2 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 N 2 O mole fractions, diurnal cycles, and possible sources of N 2 O during a period of time affected by the COVID-19 pandemic. The data show a pattern of elevated N 2 O 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 N 2 O as a recreational drug. The National Atmospheric Emissions Inventory (NAEI) reports UK emissions for recreational N 2 O 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 N 2 O in each canister and the number of times the drug is used at each sitting. Our urban measurement found that recreational use became an unnecessary anthropogenic source of N 2 O, and that the UK emission inventory provided a significant underestimate of this source.