The application of a cavity ring-down spectrometer to measurements of ambient ammonia using traceable primary standard gas mixtures

Abstract

A correction for the undesirable effects of direct and indirect cross-interference from water vapour on ammonia (NH 3) measurements was developed using an optical laser sensor based on cavity ring-down spectroscopy (CRDS). This correction relied on new measurements of the collisional broadening due to water vapour of two NH 3 spectral lines in the near infra-red (6548.6 and 6548.8 cm −1), and on the development of novel stable Primary Standard Gas Mixtures (PSMs) of ammonia prepared by gravimetry in passivated gas cylinders at 100 μmol mol −1. The PSMs were diluted dynamically to provide calibration mixtures of dry and humidified ammonia atmospheres of known composition in the nmol mol −1 range, and were employed as part of establishing a metrological traceability chain to improve the reliability and accuracy of ambient ammonia measurements. The successful implementation of this correction will allow the extension of this rapid on-line spectroscopic technique to exposure chamber validation tests under controlled conditions and ambient monitoring in the field.

Tall Tower Ammonia Observations and Emission Estimates in the U.S. Midwest

“…Through laboratory testing of the NH 3 analyzer we observed spectral interference between the water vapor and NH 3 channels, where an increase in water vapor mixing ratio caused an increase in the recorded NH 3 mixing ratio. This type of spectral interference has been observed in similar analyzers used to measure NH 3 and stable isotopes of carbon dioxide (Martin et al, 2016;Xu et al, 2017). Here, we characterized and corrected for this water vapor dependence based on a series of calibration tests with varying water vapor mixing ratios.…”

High-precision atmospheric oxygen measurement comparisons between a newly built CRDS analyzer and existing measurement techniques

“…The analyzer described here is derived from the Picarro G2000 series of CRDS analyzers. The basic elements have been described elsewhere (Crosson, 2008;Martin et al, 2016;Steig et al, 2014); briefly, the instrument is built around a high-finesse, traveling-wave optical cavity, which is coupled to one of two single-frequency distributed feedback-stabilized semiconductor lasers. One cavity mirror is mounted on a piezoelectric translator (PZT) to allow fine tuning of the cavity resonance frequencies.…”

“…Therefore, another gas component in the breath air must be responsible for the abovementioned interference. Based on the absorption lines in the spectral range of the instrument (7878 cm −1 ) retrieved from the HITRAN database, we expect the interference to stem from either carbon monoxide (now excluded by the tests), methane, or volatile organic compounds including acetone, ethanol, methanol, or isoprenes -all of which have been measured in breath air (Gao et al, 2017;Gottlieb et al, 2017;Mckay et al, 1985;Ryter and Choi, 2013;Wolf et al, 2017). Further investigations are required to shed light on these interferences in order to take corresponding action to surpass these shortcomings in the isotope analysis based on cavity ring-down spectroscopy.…”

Measurement of ammonia, amines and iodine species using protonated water cluster chemical ionization mass spectrometry

“…The PICARRO was also independently calibrated with a NH3 permeation tube (Fine Metrology, Italy) using a multigas calibrator (SONIMIX 6000 C1, LNI Swissgas, Switzerland). The time interval for one measurement of the PICARRO is 5 seconds for which a lower detection limit of 200 pptv is reported 225 (PICARRO Inc., USA; Martin et al, 2016). ion in the mass spectrum.…”