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Discussion papers | Copyright
https://doi.org/10.5194/amt-2018-2
© Author(s) 2018. This work is distributed under
the Creative Commons Attribution 4.0 License.

Research article 01 Mar 2018

Research article | 01 Mar 2018

Review status
This discussion paper is a preprint. It is a manuscript under review for the journal Atmospheric Measurement Techniques (AMT).

The Effect of Instrumental Stray Light on Brewer and Dobson Total Ozone Measurements

Omid Moeini1,2, Zahra Vaziri1, C. Thomas McElroy1, David W. Tarasick2, Robert D. Evans3, Irina Petropavlovskikh3, and Keh-Harng Feng1 Omid Moeini et al.
  • 1Department of Earth and Space Science and Engineering, Lassonde School of Engineering, and the Centre for Research in Earth and Space Science , York University, Toronto, ON, Canada
  • 2Air Quality Research Division, Enviro nment and Climate Change Canada, Toronto, ON, Canada
  • 3Global Monitoring Division, NOAA Earth System Research Laboratory, Boulder, CO, USA

Abstract. Dobson and Brewer spectrophotometers are the primary, standard instruments for ground‐based ozone measurements under the World Meteorological Organization’s (WMO) Global Atmosphere Watch program. The accuracy of the data retrieval for both instruments depends on a knowledge of the ozone absorption coefficients and some assumptions underlying the data analysis. Instrumental stray light causes non-linearity in the response of both the Brewer and Dobson to ozone at large ozone slant paths. In addition, it affects the effective ozone absorption coefficients and extraterrestrial constants that are both instrument dependent. This effect has not been taken into account in the calculation of ozone absorption coefficients that are currently recommended by WMO for the Dobson network. The ozone absorption coefficients are calculated for each Brewer instrument individually, but in the current procedure the effect of stray light is not being considered. This study documents the error caused by the effect of stray light in the Brewer and Dobson total ozone measurements using a mathematical model for each instrument. For the first time, new ozone absorption coefficients are calculated for the Brewer and Dobson instruments taking into account the stray light effect. The analyses show that the differences detected between the total ozone amounts deduced from Dobson AD and CD pair wavelengths are related to the level of stray light within the instrument. The error introduced by the assumption of a fixed height for the ozone layer for ozone measurements at high latitude sites is also evaluated. The ozone data collected by three Dobson instruments between 2008 and 2012 are compared with ozone data from a collocated double monochromator Brewer spectrophotometer (Mark III). The results show the dependence of Dobson AD and CD pair measurements on stray light.

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This study documents the error caused by the effect of stray light in the Brewer and Dobson total ozone measurements using a mathematical model for each instrument. The errors caused by stray light are particularly significant at high latitudes in the late winter and early spring when measurements are made at large solar zenith angles and large total ozone column. It is considerable importance if those data are to be used for trend analysis or satellite data validation.
This study documents the error caused by the effect of stray light in the Brewer and Dobson...
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