Accuracy, precision, and temperature dependence of Pandora total ozone measurements estimated from a comparison with the Brewer triad in Toronto

Abstract

Abstract. This study evaluates the performance of the recently developed Pandora spectrometer by comparing it with the Brewer reference triad. This triad was established by Environment and Climate Change Canada (ECCC) in the 1980s and is used to calibrate Brewer instruments around the world, ensuring high-quality total column ozone (TCO) measurements. To reduce stray light, the double Brewer instrument was introduced in 1992, and a new reference triad of double Brewers is also operational at Toronto. Since 2013, ECCC has deployed two Pandora spectrometers co-located with the old and new Brewer triads, making it possible to study the performance of three generations of ozone-monitoring instruments. The statistical analysis of TCO records from these instruments indicates that the random uncertainty for the Brewer is below 0.6 %, while that for the Pandora is below 0.4 %. However, there is a 1 % seasonal difference and a 3 % bias between the standard Pandora and Brewer TCO data, which is related to the temperature dependence and difference in ozone cross sections. A statistical model was developed to remove this seasonal difference and bias. It was based on daily temperature profiles from the European Centre for Medium-Range Weather Forecasts ERA-Interim data over Toronto and TCO from the Brewer reference triads. When the statistical model was used to correct Pandora data, the seasonal difference was reduced to 0.25 % and the bias was reduced to 0.04 %. Pandora instruments were also found to have low air mass dependence up to 81.6 • solar zenith angle, comparable to double Brewer instruments.

Intercomparison of total column ozone data from the Pandora spectrophotometer with Dobson, Brewer, and OMI measurements over Seoul, Korea

“…Consequently, daily and real-time total ozone data measured by the Pandora spectrophotometer show high reliability and are expected to improve substantially with the regular, accurate calibration and validation associated with the operational monitoring of trace gases and pollutants. The underestimation of PAN TCO in long-optical-path-length cases in Seoul can be attributed to the enhancement of aerosol scattering and the stray-light effect of the instrument, which is similar to previous comparison studies in Herman et al (2015) and Zhao et al (2016). However, detailed reasons for TCO underestimation for large SZAs still require further studies.…”

“…These characteristics by optical geometry partially affect reducing sensitivity of TCO retrieval in both BRE and PAN. In addition, Zhao et al (2016) analyzed that PAN data have negligible air mass dependence when the ozone AMF < 3. For the large-AMF cases, the stray-light effect in the instrument detector affects the accuracy of total ozone retrieval Tzortziou et al, 2012) with its dependence on slant column amounts of ozone.…”

Cyclone-induced surface ozone and HDO depletion in the Arctic

“…69 analysed using the standard Brewer network operational algorithm (Kerr, 2002), with small changes to the analysis parameters due to the high latitude of the site. Normally, high-quality Brewer TCO data need an ozone air mass factor (AMF) less than 3 (Fioletov et al, 2000;Zhao et al, 2016b). However, to cope with the low-sun condition in the high-latitude spring, following Adams et al (2012a), the ozone AMF threshold was increased to 5, which is acceptable under low ozone conditions and allows for more days with good data in the early spring.…”

“…However, to cope with the low-sun condition in the high-latitude spring, following Adams et al (2012a), the ozone AMF threshold was increased to 5, which is acceptable under low ozone conditions and allows for more days with good data in the early spring. The uncertainty in Brewer TCO measurements is typically less than 1 % (Fioletov et al, 2005), and for high-quality data (e.g., AMF < 3) less than 0.6 % (Zhao et al, 2016b). The EWS has records of electrochemical concentration cell (ECC) ozonesonde measurements since 1992 (Tarasick et al, 2016).…”

Response to Referee #2

“…The Brewer instrument is the World Meteorological Organization (WMO) Global Atmosphere Watch (GAW) standard for total column ozone measurement (Kerr et al, 1981(Kerr et al, , 1988 (Kerr, 2002), with small changes to the analysis parameters due to the high latitude of the site. Normally, high-quality Brewer TCO data need an ozone air mass factor (AMF) less than 3 (Fioletov et al, 2000;Zhao et al, 2016b). However, to cope with the low-sun condition in the high-latitude spring, following Adams et al (2012a), the ozone AMF threshold was increased to 5, which is acceptable under low ozone conditions and allows for more days with good data in the early spring.…”