New estimates of nitrous oxide emissions from biomass burning

Abstract

ATMOSPHERIC nitrous oxide is important because of its role in stratospheric ozone destruction¹ and because it is a greenhouse gas.^2,3. Measurements indicate that N₂O is increasing in the atmosphere at a rate of ~0.2% yr"¹ (ref. ⁴). Fossil-fuel combustion and biomass burning^5,6 have been considered to be significant global sources of N₂O, but the recent discovery of an artefact producing increased levels of N₂O in combustion gas samples collected and stored in grab bottles before chemical analysis^7,8has resulted in the downgrading of fossil-fuel combustion and the questioning of biomass burning as important sources of N₂O^9,10. As almost all reported analyses of N₂O produced from biomass burning have involved essentially the same collection and analysis protocols as used in the fossil-fuel studies, this source of N₂O must also be re-examined. Here we report and compare measurements of N₂O made over a large prescribed fire using a near real-time in situ measurement technique with measurements of N₂O from simultaneously collected grab-bottle samples. The results from 27 small laboratory biomass test fires also help clarify the validity of earlier assessments. We conclude that biomass burning contributes -7% of atmospheric N₂O, as opposed to earlier estimates of several times this value⁶.