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

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