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| Titel |
Laboratory evaluation of the effect of nitric acid uptake on frost point hygrometer performance |
| VerfasserIn |
T. Thornberry, T. Gierczak, R. S. Gao, H. Vömel, L. A. Watts, J. B. Burkholder, D. W. Fahey |
| Medientyp |
Artikel
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| Sprache |
Englisch
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| ISSN |
1867-1381
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| Digitales Dokument |
URL |
| Erschienen |
In: Atmospheric Measurement Techniques ; 4, no. 2 ; Nr. 4, no. 2 (2011-02-15), S.289-296 |
| Datensatznummer |
250001675
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| Publikation (Nr.) |
 copernicus.org/amt-4-289-2011.pdf |
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| Zusammenfassung |
| 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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