Articles | Volume 7, issue 1
Atmos. Meas. Tech., 7, 81–93, 2014
https://doi.org/10.5194/amt-7-81-2014
Atmos. Meas. Tech., 7, 81–93, 2014
https://doi.org/10.5194/amt-7-81-2014

Research article 13 Jan 2014

Research article | 13 Jan 2014

Open-path, quantum cascade-laser-based sensor for high-resolution atmospheric ammonia measurements

D. J. Miller1,2, K. Sun1,2, L. Tao1,2, M. A. Khan1,2,*, and M. A. Zondlo1,2 D. J. Miller et al.
  • 1Department of Civil and Environmental Engineering, Princeton University, Princeton, NJ 08540, USA
  • 2Center for Mid-Infrared Technologies for Health and the Environment, NSF-ERC, Princeton, NJ, USA
  • *now at: Delaware State University, Dover, DE 19901, USA

Abstract. We demonstrate a compact, open-path, quantum cascade-laser-based atmospheric ammonia sensor operating at 9.06 μm for high-sensitivity, high temporal resolution, ground-based measurements. Atmospheric ammonia (NH3) is a gas-phase precursor to fine particulate matter, with implications for air quality and climate change. Currently, NH3 sensing challenges have led to a lack of widespread in situ measurements. Our open-path sensor configuration minimizes sampling artifacts associated with NH3 surface adsorption onto inlet tubing and reduced pressure sampling cells, as well as condensed-phase partitioning ambiguities. Multi-harmonic wavelength modulation spectroscopy allows for selective and sensitive detection of atmospheric pressure-broadened absorption features. An in-line ethylene reference cell provides real-time calibration (±20% accuracy) and normalization for instrument drift under rapidly changing field conditions. The sensor has a sensitivity and noise-equivalent limit (1σ) of 0.15 ppbv NH3 at 10 Hz, a mass of ~ 5 kg and consumes ~ 50 W of electrical power. The total uncertainty in NH3 measurements is 0.20 ppbv NH3 ± 10%, based on a spectroscopic calibration method. Field performance of this open-path NH3 sensor is demonstrated, with 10 Hz time resolution and a large dynamic response for in situ NH3 measurements. This sensor provides the capabilities for improved in situ gas-phase NH3 sensing relevant for emission source characterization and flux measurements.

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