An improved open-top dynamic chambers method for measuring the exchange fluxes of N2O, NO and NH3 from farmland.

The application of nitrogen fertilizers in agricultural fields can lead to the release of nitrogen-containing gases (NCGs), such as NOx, NH3 and N2O, which can significantly impact regional atmospheric environment and contribute to global climate change. However, there remain considerable research gaps in the accurate measurement of NCGs emissions from agricultural fields, hindering the development of effective emission reduction strategies. We improved an open-top dynamic chambers (OTDCs) system and evaluated the performance by comparing the measured and given fluxes of the NCGs. The results showed that the measured fluxes of NO, N2O and NH3 were 1 %, 2 % and 7 % lower than the given fluxes, respectively. For the determination of NH3 concentration, we employed a stripping coil-ion chromatograph (SC-IC) analytical technique, which demonstrated an absorption efficiency for atmospheric NH3 exceeding 96.1 % across sampling durations of 6 to 60 min. In the summer maize season, we utilized the OTDCs system to measure the exchange fluxes of NO, NH3, and N2O from the soil in the North China Plain. Substantial emissions of NO, NH3 and N2O were recorded following fertilization, with peaks of 107, 309, 1239 ng N/(m2·s), respectively. Notably, significant NCGs emissions were observed following sustained heavy rainfall one month after fertilization, particularly with NH3 peak being 4.5 times higher than that observed immediately after fertilization. Our results demonstrate that the OTDCs system accurately reflects the emission characteristics of soil NCGs and meets the requirements for long-term and continuous flux observation.