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.