Continuous measurements of nitrous oxide in the troposphere

Abstract

CONTINUOUS measurements of N₂O at the ground surface by Brice, et al.¹ have been interpreted as “evidence for the existence of an appreciable, but unidentified, ground surface sink mechanism”. They based this conclusion on an apparent regular diurnal variation in the concentration of N₂O in the air 5 m above the ground, observed during the periods 24–29 July and 4–8 August 1976. “A minimum was nearly always recorded in the early hours of the morning and a maximum was recorded in the late afternoon or evening.”¹ In contrast to these results, Cicerone, et al.² reported N₂O measurements made during 25–27 May and 29 August–1 September 1977 which show exactly the opposite behaviour, suggesting instead “that the 1200–1800 h time period sees significantly (at the 1σlevel) lower N₂O concentrations than does the period 0000–0600 h LT”. Contrary to both these results, we made continuous measurements of tropospheric N₂O for a full year and found no significant diurnal variation in the atmospheric level of N₂O. The only diurnal variation we observed was an experimental artefact created by the diurnal variation in the ambient temperature affecting the sensitivity of the instrument.