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Atmospheric Measurement Techniques An interactive open-access journal of the European Geosciences Union
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Volume 4, issue 2
Atmos. Meas. Tech., 4, 289–296, 2011
https://doi.org/10.5194/amt-4-289-2011
© Author(s) 2011. This work is distributed under
the Creative Commons Attribution 3.0 License.
Atmos. Meas. Tech., 4, 289–296, 2011
https://doi.org/10.5194/amt-4-289-2011
© Author(s) 2011. This work is distributed under
the Creative Commons Attribution 3.0 License.

Research article 15 Feb 2011

Research article | 15 Feb 2011

Laboratory evaluation of the effect of nitric acid uptake on frost point hygrometer performance

T. Thornberry1,2, T. Gierczak1,2,4, R. S. Gao1, H. Vömel3, L. A. Watts1,2, J. B. Burkholder1, and D. W. Fahey1,2 T. Thornberry et al.
  • 1NOAA Earth System Research Laboratory, Chemical Sciences Division, Boulder, CO, USA
  • 2Cooperative Institute for Research in Environmental Sciences, University of Colorado, Boulder, CO, USA
  • 3Meteorologisches Observatorium Lindenberg, German Weather Service, Lindenberg, Germany
  • 4University of Warsaw, Department of Chemistry, Warsaw, Poland

Abstract. Chilled mirror hygrometers (CMH) are widely used to measure water vapour in the troposphere and lower stratosphere from balloon-borne sondes. Systematic discrepancies among in situ water vapour instruments have been observed at low water vapour mixing ratios (<5 ppm) in the upper troposphere and lower stratosphere (UT/LS). Understanding the source of the measurement discrepancies is important for a more accurate and reliable determination of water vapour abundance in this region. We have conducted a laboratory study to investigate the potential interference of gas-phase nitric acid (HNO3) with the measurement of frost point temperature, and consequently the water vapour mixing ratio, determined by CMH under conditions representative of operation in the UT/LS. No detectable interference in the measured frost point temperature was found for HNO3 mixing ratios of up to 4 ppb for exposure times up to 150 min. HNO3 was observed to co-condense on the mirror frost, with the adsorbed mass increasing linearly with time at constant exposure levels. Over the duration of a typical balloon sonde ascent (90–120 min), the maximum accumulated HNO3 amounts were comparable to monolayer coverage of the geometric mirror surface area, which corresponds to only a small fraction of the actual frost layer surface area. This small amount of co-condensed HNO3 is consistent with the observed lack of HNO3 interference in the frost point measurement because the CMH utilizes significant reductions (>10%) in surface reflectivity by the condensate to determine H2O.

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