Ammonia (NH₃) in the atmosphere affects both the environment and human health. It is therefore increasingly recognised by policy makers as an important air pollutant that needs to be mitigated, though it still remains unregulated in many countries. In order to understand the effectiveness of abatement strategies, routine NH₃ monitoring is required. Current reference protocols, first developed in the 1990s, use daily samplers with offline analysis; however, there have been a number of technologies developed since, which may be applicable for high time resolution routine monitoring of NH₃ at ambient concentrations. The following study is a comprehensive field intercomparison held over an intensively managed grassland in southeastern Scotland using currently available methods that are reported to be suitable for routine monitoring of ambient NH₃. In total, 13 instruments took part in the field study, including commercially available technologies, research prototype instruments, and legacy instruments. Assessments of the instruments' precision at low concentrations (< 10 ppb) and at elevated concentrations (maximum reported concentration of 282 ppb) were undertaken. At elevated concentrations, all instruments performed well and with precision (r² > 0.75). At concentrations below 10 ppb, however, precision decreased, and instruments fell into two distinct groups, with duplicate instruments split across the two groups. It was found that duplicate instruments performed differently as a result of differences in instrument setup, inlet design, and operation of the instrument.New metrological standards were used to evaluate the accuracy in determining absolute concentrations in the field. A calibration-free CRDS optical gas standard (OGS, PTB, DE) served as an instrumental reference standard, and instrument operation was assessed against metrological calibration gases from (i) a permeation system (ReGaS1, METAS, CH) and (ii) primary standard gas mixtures (PSMs) prepared by gravimetry (NPL, UK). This study suggests that, although the OGS gives good performance with respect to sensitivity and linearity against the reference gas standards, this in itself is not enough for the OGS to be a field reference standard, because in field applications, a closed path spectrometer has limitations due to losses to surfaces in sampling NH₃, which are not currently taken into account by the OGS. Overall, the instruments compared with the metrological standards performed well, but not every instrument could be compared to the reference gas standards due to incompatible inlet designs and limitations in the gas flow rates of the standards.This work provides evidence that, although NH₃ instrumentation have greatly progressed in measurement precision, there is still further work required to quantify the accuracy of these systems under field conditions. It is the recommendation of this study that the use of instruments for routine monitoring of NH₃ needs to be set out in standard operating protocols for inlet setup, calibration, and routine maintenance in order for datasets to be comparable.

中文翻译：

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环境 NH3 原位测量的相互比较：现场条件下的仪器性能和应用

大气中的氨 (NH ₃ ) 会影响环境和人类健康。因此，政策制定者越来越认识到它是一种需要减轻的重要空气污染物，尽管它在许多国家仍未受到监管。为了了解减排策略的有效性，需要进行常规 NH ₃监测。当前的参考协议最初于 1990 年代开发，使用每日采样器进行离线分析；然而，自那以后已经开发出许多技术，这些技术可能适用于 NH _{3的高时间分辨率常规监测}在环境浓度。以下研究是对苏格兰东南部集约化管理的草地进行的综合现场比对，使用的方法据报道适用于环境 NH ₃的常规监测。总共有 13 台仪器参与了现场研究，包括商用技术、研究原型仪器和遗留仪器。对仪器在低浓度 ( <  10 ppb) 和高浓度（报告的最大浓度为 282 ppb）下的精度进行了评估。在高浓度下，所有仪器都表现良好且精度高 ( r ²  > 0.75）。然而，当浓度低于 10 ppb 时，精度下降，仪器分为两个不同的组，重复的仪器分为两组。结果发现，由于仪器设置、入口设计和仪器操作的差异，重复仪器的性能不同。新的计量标准用于评估确定现场绝对浓度的准确性。免校准 CRDS 光学气体标准（OGS、PTB、DE）用作仪器参考标准，并根据来自（i）渗透系统（ReGaS1、METAS、CH）和（ii）初级的计量校准气体评估仪器操作通过重力法制备的标准气体混合物 (PSM)（NPL，英国）。这项研究表明，₃，目前 OGS 未考虑这些。总的来说，与计量标准相比，仪器表现良好，但由于入口设计不兼容以及标准气体流速的限制，并非每台仪器都可以与参考气体标准进行比较。这项工作提供的证据表明，尽管 NH ₃仪器尽管在测量精度方面取得了很大进步，但仍需要进一步的工作来量化这些系统在现场条件下的精度。本研究建议，需要在入口设置、校准和日常维护的标准操作规程中规定用于_{NH 3常规监测的仪器的使用，以便数据集具有可比性。}