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Atmospheric Measurement Techniques An interactive open-access journal of the European Geosciences Union
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Volume 11, issue 5 | Copyright
Atmos. Meas. Tech., 11, 2537-2551, 2018
© Author(s) 2018. This work is distributed under
the Creative Commons Attribution 4.0 License.

Research article 03 May 2018

Research article | 03 May 2018

A steady-state continuous flow chamber for the study of daytime and nighttime chemistry under atmospherically relevant NO levels

Xuan Zhang1,*, John Ortega1,*, Yuanlong Huang2, Stephen Shertz1, Geoffrey S. Tyndall1, and John J. Orlando1 Xuan Zhang et al.
  • 1Atmospheric Chemistry Observation & Modeling Laboratory (ACOM), National Center for Atmospheric Research (NCAR), Boulder, CO, USA
  • 2Department of Environmental Science and Engineering, California Institute of Technology, Pasadena, CA, USA
  • *These authors contributed equally to this work.

Abstract. Experiments performed in laboratory chambers have contributed significantly to the understanding of the fundamental kinetics and mechanisms of the chemical reactions occurring in the atmosphere. Two chemical regimes, classified as high-NO vs. zero-NO conditions, have been extensively studied in previous chamber experiments. Results derived from these two chemical scenarios are widely parameterized in chemical transport models to represent key atmospheric processes in urban and pristine environments. As the anthropogenic NOx emissions in the United States have decreased remarkably in the past few decades, the classic high-NO and zero-NO conditions are no longer applicable to many regions that are constantly impacted by both polluted and background air masses. We present here the development and characterization of the NCAR Atmospheric Simulation Chamber, which is operated in steady-state continuous flow mode for the study of atmospheric chemistry under intermediate NO conditions. This particular chemical regime is characterized by constant sub-ppb levels of NO and can be created in the chamber by precise control of the inflow NO concentration and the ratio of chamber mixing to residence timescales. Over the range of conditions achievable in the chamber, the lifetime of peroxy radicals (RO2), a key intermediate from the atmospheric degradation of volatile organic compounds (VOCs), can be extended to several minutes, and a diverse array of reaction pathways, including unimolecular pathways and bimolecular reactions with NO and HO2, can thus be explored. Characterization experiments under photolytic and dark conditions were performed and, in conjunction with model predictions, provide a basis for interpretation of prevailing atmospheric processes in environments with intertwined biogenic and anthropogenic activities. We demonstrate the proof of concept of the steady-state continuous flow chamber operation through measurements of major first-generation products, methacrolein (MACR) and methyl vinyl ketone (MVK), from OH- and NO3-initiated oxidation of isoprene.

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Short summary
We present the development and characterization of the NCAR Atmospheric Simulation Chamber, which is operated in steady state continuous flow mode for simulating atmospheric daytime and nighttime chemistry over chemical regimes not accessible in traditional static chamber experiments. We focus on establishing an intermediate NO regime characterized by a constant steady-state NO level ranging from tens of ppt to a few ppb in the chamber.
We present the development and characterization of the NCAR Atmospheric Simulation Chamber,...