Intercomparison of in situ measurements of ambient NH₃: instrument performance and application under field conditions

Abstract

Abstract. 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.

Unraveling Ammonia and Trimethylamine Uptake on Conductive Doped Polyaniline

“…4 Typical ambient concentrations range from 0.3 to hundreds of ppb when close to sources; however, most of the time they are under 10 ppb. 6 In industrial environments, NH 3 is a threat to workers' health at concentrations over 25 ppm. 7 It can also be an issue for industrial applications at a much lower concentration.…”

“…Atmospheric ammonia emissions can lead to the deposition of acid rain but can also combine with sulfur oxides and nitrogen oxides to form fine particles . Typical ambient concentrations range from 0.3 to hundreds of ppb when close to sources; however, most of the time they are under 10 ppb . In industrial environments, NH 3 is a threat to workers’ health at concentrations over 25 ppm .…”

Measurement report: Ammonia in Paris derived from ground-based open-path and satellite observations

“…Models have difficulty predicting events of particulate pollution associated with NH 3 since ground-based atmospheric observations of this gas are still relatively sparse (Nair and Yu, 2020) and difficult to implement (Twigg et al, 2022;von Bobrutzki et al, 2010). To our knowledge, only six countries in the world (the United States, China, the Netherlands, the United Kingdom, Belgium, and Canada) have dedicated NH 3 observations in their atmospheric monitoring networks.…”

An uncertainty methodology for solar occultation flux measurements: ammonia emissions from agriculture

“…Consequently, NH3 has gained attention over the last few decades, thus increasing the development of instruments and models used to study its emission sources. Moreover, with improvements in infrared lasers, spectroscopy-based instruments have emerged, such as FTIRs (Fourier Transform infrared spectrometers), cavity ring-down spectrometers (CSDRs) and quantum cascade laser absorption spectrometers (QCLASs) (Twigg et al, 2022). NH3 concentrations are challenging to quantify due to its strong reactivity, which makes the gas molecule adhere to surfaces and requires that close-path instruments and inlets are coated or heated to decrease the response delay (Zhu et al, 2015b).…”

“…NH3 concentrations are challenging to quantify due to its strong reactivity, which makes the gas molecule adhere to surfaces and requires that close-path instruments and inlets are coated or heated to decrease the response delay (Zhu et al, 2015b). A study using 13 instruments highlighted the importance of its setup, inlet design and operation (flow rate and filter status), as these factors can affect measurement performance (Twigg et al, 2022).…”