Intercomparison of ultraviolet photometry and
gas-phase titration techniques for ozone reference standards at ambient
levels
Tanimoto, H., H. Mukai, S. Hashimoto, J.E. Norris (2006)
[Abstract]
Experiments were conducted to compare two independent techniques for
obtaining ozone (O3) reference standards often used as the primary standard
in air quality monitoring networks. The two techniques were ultraviolet
absorption photometry of O3 at the 253.7-nm Hg line and gas-phase titration
of O3 with excess NO. For ultraviolet photometry, a well-designed and
maintained standard reference photometer (SRP) built by the National
Institute of Standards and Technology (USA) was employed. For gas-phase
titration (GPT), an existing system was significantly modified by the
National Institute for Environmental Studies (Japan) by using gravimetric
NO/N2 standard gases, accurate flow measurement systems based on laminar
flow elements, and two chemiluminescence NO detectors to minimize uncertainty
in the measurements, which had previously been a major shortcoming of
this method. Uncertainty in the improved GPT system was reduced to less
than 0.4% above 100 nmol mol-1 O3 mole fraction. A series of comparison
runs between the two methods over the course of the 13 months from August
2004 to August 2005 showed a significant discrepancy, which cannot be
explained by the measurement uncertainties attributed to either SRP
or GPT in the range of 80-800 nmol mol-1 O3, where GPT was about 2%
higher than SRP. This result indicates possible biases in the currently
existing O3 reference standards and warrants further study to identify
and characterize possible sources of the systematic discrepancy.
Tanimoto, H., H. Mukai, S. Hashimoto, J.E. Norris (2006) Intercomparison
of ultraviolet photometry and gas-phase titration techniques for ozone
reference standards at ambient levels. J. Geophys. Res., 111, D16313,
doi:10. 1029/2005JD006983.
Link to the abstract of the article
http://www.agu.org/pubs/crossref/2006/2005JD006983.shtml
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