Examination on total ozone column retrievals by Brewer spectrophotometry using different processing software

Abstract

Abstract. The availability of long-term records of the total ozone content (TOC) represents a valuable source of information for studies on the assessment of short- and long-term atmospheric changes and their impact on the terrestrial ecosystem. In particular, ground-based observations represent a valuable tool for validating satellite-derived products. To our knowledge, details about software packages for processing Brewer spectrophotometer measurements and for retrieving the TOC are seldom specified in studies using such datasets. The sources of the differences among retrieved TOCs from the Brewer instruments located at the Italian stations of Rome and Aosta, using three freely available codes (Brewer Processing Software, BPS; O3Brewer software; and European Brewer Network (EUBREWNET) level 1.5 products) are investigated here. Ground-based TOCs are also compared with Ozone Monitoring Instrument (OMI) TOC retrievals used as an independent dataset since no other instruments near the Brewer sites are available. The overall agreement of the BPS and O3Brewer TOC data with EUBREWNET data is within the estimated total uncertainty in the retrieval of total ozone from a Brewer spectrophotometer (1 %). However, differences can be found depending on the software in use. Such differences become larger when the instrumental sensitivity exhibits a fast and dramatic drift which can affect the ozone retrievals significantly. Moreover, if daily mean values are directly generated by the software, differences can be observed due to the configuration set by the users to process single ozone measurement and the rejection rules applied to data to calculate the daily value. This work aims to provide useful information both for scientists engaged in ozone measurements with Brewer spectrophotometers and for stakeholders of the Brewer data products available on Web-based platforms.

Solar UV Irradiance in a Changing Climate: Trends in Europe and the Significance of Spectral Monitoring in Italy

“…The standard uncertainty (for wavelengths above 305 nm and solar zenith angles (SZA) below 75 • ) of the UV spectra is estimated as 5% for Rome and 3% for Aosta [96,106]. The accuracy of the total ozone measurements from Brewer spectrophotometers is estimated to be 1% [118,119]. Spectra from the two stations have been processed using the SHICrivm algorithm [120] in order to correct them for the effect of wavelength shift, and extend the spectra up to 400 nm for Brewer #067 (in order to calculate erythemal irradiance).…”

“…Total ozone data from the Brewer#067 and the Brewer with serial number 66 (Brewer#066) were analyzed for Rome and Aosta respectively. UV and total ozone datasets from the two stations have all been subjected to quality control/quality assurance (QC/QA), and are traceable to international reference standards [97,106,118]. The standard uncertainty (for wavelengths above 305 nm and solar zenith angles (SZA) below 75 • ) of the UV spectra is estimated as 5% for Rome and 3% for Aosta [96,106].…”

Aerosol optical characteristics in the urban area of Rome, Italy, and their impact on the UV index

“…CC BY 4.0 License. (Siani et al, 2018). Yet, individual total ozone values were discarded when standard deviation is above 2.5 DU and ozone air mass (defined as the ratio of the actual ozone path length taken by the direct solar beam to the analogous vertical ozone path when the Sun is overhead from the surface to the top of the atmosphere) is above 3.5.…”

Solar UV Irradiance in a Changing Climate: Trends in Europe and the Significance of Spectral Monitoring in Italy

“…The standard uncertainty (for wavelengths above 305 nm and SZAs below 75°) of the UV spectra is estimated as 5% for Rome and 3% for Aosta [94,104]. The accuracy of the total ozone measurements from Brewer spectrophotometers is estimated to be ~1% [116,117]. Spectra from the two stations have been processed using the SHICrivm algorithm [118] in order to correct them for the effect of wavelength shift, and extend the spectra up to 400 nm for Brewer #067 (in order to calculate erythemal irradiance).…”

“…Total ozone data from the Brewer#067 and the Brewer with serial number 66 (Brewer#066) have been analyzed for Rome and Aosta respectively. UV and total ozone datasets from the two stations have all been subjected to quality control/quality assurance (QC/QA), and are traceable to international reference standards [95,104,116]. The standard uncertainty (for wavelengths above 305 nm and SZAs below 75°) of the UV spectra is estimated as 5% for Rome and 3% for Aosta [94,104].…”