@article{1211,
  author = {D. Miller and K. Sun and L. Tao and M. Khan and M. Zondlo},
  title = {Open-path, quantum cascade-laser-based sensor for high-resolution atmospheric ammonia measurements},
  abstract = {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 ({\textpm}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 \textasciitilde 5 kg and consumes \textasciitilde 50 W of electrical power. The total uncertainty in NH3 measurements is 0.20 ppbv NH3 {\textpm} 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.},
  year = {2014},
  journal = {Atmospheric Measurement Techniques},
  volume = {7},
  number = {1},
  pages = {81{\textendash}93},
  month = {jan},
  issn = {1867-8548},
  url = {https://amt.copernicus.org/articles/7/81/2014/},
  doi = {10.5194/amt-7-81-2014},
  language = {en},
}