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Atmospheric Measurement Techniques An interactive open-access journal of the European Geosciences Union
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Preprints
https://doi.org/10.5194/amt-2020-187
© Author(s) 2020. This work is distributed under
the Creative Commons Attribution 4.0 License.
https://doi.org/10.5194/amt-2020-187
© Author(s) 2020. This work is distributed under
the Creative Commons Attribution 4.0 License.

  25 May 2020

25 May 2020

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A revised version of this preprint was accepted for the journal AMT and is expected to appear here in due course.

Measurement of NOx and NOy with a thermal dissociation cavity ring-down spectrometer (TD-CRDS): Instrument characterisation and first deployment

Nils Friedrich1, Ivan Tadic1, Jan Schuladen1, James Brooks2, Eoghan Darbyshire2, Frank Drewnick1, Horst Fischer1, Jos Lelieveld1, and John N. Crowley1 Nils Friedrich et al.
  • 1Atmospheric Chemistry Department, Max Planck Institute for Chemistry, Mainz, 55128, Germany
  • 2Centre of Atmospheric Science, University of Manchester, Manchester, UK

Abstract. We present a newly constructed, two channel Thermal Dissociation Cavity Ring-Down Spectrometer (TD-CRDS) for the detection of NOx (NO + NO2), NOy (NOx + HNO3 + RO2NO2 + N2O5 etc.), NOz (NOy – NOx) and particulate nitrate (pNit). NOy-containing trace gases are detected as NO2 by CRDS at 405 nm following sampling through inlets at ambient temperature (NOx), or at 850 °C (NOy). In both cases, O3 was added to the air sample directly upstream of the cavities to convert NO (either ambient, or formed in the 850 °C oven) to NO2. An activated carbon denuder was used to remove gas-phase components of NOy when sampling pNit. Detection limits (1 minute averaging) for NOx, NOy and NOz are 98, 51 and 110 pptv, respectively. The total measurement uncertainties (at 50 % RH) in the NOx and NOy channels are 11 % + 10 pptv and 16 % + 14 pptv for NOz, respectively. Thermograms of various NOz species (peroxyacetyl nitrate, isopropyl nitrate, and HNO3) confirm stoichiometric conversion to NO2 (and/or NO) at the oven temperature and rule out significant interferences from NH3 detection or radical recombination reactions under ambient conditions. While fulfilling the requirement of high particle transmission and essentially complete removal of reactive nitrogen under dry conditions, the denuder suffered from NOx breakthrough and memory effects (i.e. release of stored NOy) under humid conditions.

NOx measurements obtained from a ship sailing through the Red Sea, Indian Ocean and Arabian Gulf (NOx levels from < 20 pptv to 25 ppbv) were in excellent agreement with those taken by a chemiluminescence detector of NO and NO2. A dataset exploring variations in the NOz to NOy ratio (maximum value of 0.6) of air in a region (Mainz, Germany) with strong urban influence was measured over a one-week period in winter.

Nils Friedrich et al.

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Nils Friedrich et al.

Nils Friedrich et al.

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Latest update: 21 Sep 2020
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Short summary
We present a new instrument for measurement of NOx and NOy based on a combination of thermal dissociation of NOy to NOx and cavity-ringdown-spectroscopy detection of NO2. It features a denuder to separate contributions of gas-phase and particulate nitrates to NOy. We describe a detailed characterization of the instrument and briefly outline results from first deployments.
We present a new instrument for measurement of NOx and NOy based on a combination of thermal...
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