Remarkable Overestimation of Soil N₂O Emission by Using Static Chambers

Atmospheric nitrous oxide (N₂O) is one of the principal greenhouse gases and the largest ozone-depleting substance in the stratosphere. The growth of the atmospheric N₂O burden has been mainly attributed to emissions from agricultural fields. However, N₂O emissions measured by using conventional static chambers (CSCs) usually suffer from serious artifacts that influence the estimations of the global N₂O budget. In this study, N₂O fluxes from an agricultural field in the North China Plain (NCP) were comparably measured by using CSCs, CSCs with dehumidification, and open-top dynamic chambers (OTDCs) to reveal the artifact of humidity accumulation inside CSCs on N₂O emissions. The air relative humidity and topsoil moisture inside the CSCs were found to be significantly higher than those inside the OTDCs and over/in the field, leading to the CSCs' overestimation of N₂O emissions by factors of 2.3-3.6. The overestimation of N₂O emissions by CSCs was further verified by soil simulation experiments in a flow tube by flushing the soil with varying air humidity. The results of this study underscore that future efforts should prioritize validating the estimates of N₂O emissions from key sources using minimally intrusive methods like dynamic chambers or micrometeorological methods.