Although biosphere-atmosphere exchanges of ammonia (NH₃) are of great environmental importance regarding, e.g., eutrophication and aerosol-related human health problems, their magnitudes are not well constrained due to the challenges in in-situ measurements of NH₃ fluxes. In this paper we introduce a portable, low-power and quantum cascade laser-based open-path analyzer for eddy covariance (EC) measurement of NH₃ fluxes particularly at sites without grid power. This analyzer minimizes the sampling artifacts due to surface adsorption of NH₃ by using an open-path optical Herriott cell configuration, while also increases its portability and convenience in field deployment by assembling most instrumental components in a highly integrated and compact enclosure. Its performance was tested through laboratory experiments and one-week EC measurements at a subtropical rice paddy. Its uncertainty in measuring NH₃ concentration is ± 15%, being comparable to those of the currently available high-sensitivity NH₃ analyzers. The flux random error averaged at 26 ± 28% during the entire experimental period. The instrumental noise of the analyzer with a sampling frequency of 10 Hz is estimated to be 0.286 and 0.302 nmol mol^‒1 (ppbv) under the laboratory and field conditions, respectively. Under the given test conditions, the detection limit of the EC system is 7.1 ± 1.1 μg N m⁻² h⁻¹ for half-hourly NH₃ flux measurement. Nearly 91% of the half-hourly fluxes observed during the experimental period were larger than the mean detection limit. Such instrumental sensitivity is adequate for quantifying NH₃ emissions from most source ecosystems, and also possible to monitor deposition fluxes at ecosystems away from strong sources with low NH₃ concentrations. Availability of this open-path NH₃ analyzer provides an access to a better understanding of the biosphere-atmosphere NH₃ exchanges and to a more reliable estimate of the NH₃ inventory at ecosystem or larger scales.

尽管氨 (NH ₃ ) 的生物圈-大气交换对于例如富营养化和与气溶胶相关的人类健康问题具有重要的环境意义，但由于NH ₃通量的原位测量中的挑战，它们的大小并未受到很好的限制。在本文中，我们介绍了一种便携式、低功率和基于量子级联激光的开路分析仪，用于 NH ₃通量的涡流协方差 (EC) 测量，特别是在没有电网电源的地点。由于 NH _{3 的}表面吸附，该分析仪最大限度地减少了采样伪影通过使用开放路径光学 Herriott 单元配置，同时还通过将大多数仪器组件组装在高度集成和紧凑的外壳中来提高其便携性和现场部署的便利性。通过实验室实验和在亚热带稻田进行的为期一周的 EC 测量对其性能进行了测试。其测量 NH ₃浓度的不确定度为 ± 15%，可与目前可用的高灵敏度 NH ₃分析仪相媲美。在整个实验期间，通量随机误差平均为 26 ± 28%。采样频率为 10 Hz 时分析仪的仪器噪声估计为 0.286 和 0.302 nmol mol ^‒1(ppbv) 分别在实验室和现场条件下。在给定的测试条件下，EC 系统的检测限为 7.1 ± 1.1 μg N m ^-2 h ^-1半小时 NH ₃通量测量。在实验期间观察到的半小时通量中有近 91% 大于平均检测限。这种仪器灵敏度足以量化来自大多数源生态系统的NH ₃排放，也可以监测远离强源且 NH ₃浓度低的生态系统的沉积通量。这种开放路径 NH ₃分析仪的可用性提供了更好地了解生物圈 - 大气 NH ₃的途径交换以及更可靠地估计生态系统或更大规模的 NH ₃存量。