Total Ozone Column From Direct And Diffuse Spectral Solar Irradiance In The Southwest Of The Iberian Peninsula

Daily total ozone column (TOC) measurements from the Brewer spectroradiometer
located at El Arenosillo (Spain) and the Spectrometer for Atmospheric TRAcers
Monitoring (SPATRAM) located at Évora (Portugal) are analyzed for the period
2006–2008. The main goal of this study is to compare TOC estimates retrieved with the
passive differential optical absorption spectroscopy (DOAS) methodology from zenith‐sky
observations by the SPATRAM spectrometer with highly accurate TOC estimates
retrieved from direct‐sun recordings by a well‐calibrated Brewer instrument. On average,
SPATRAM TOC estimates are (1.69 ± 0.18)% smaller than collocated Brewer TOC
estimates. Significant relative differences between SPATRAM and Brewer total ozone
data are detected in some periods caused by the influence of high aerosol load episodes
over the SPATRAM data. Satellite data recorded by the ozone monitoring instrument
(OMI)‐DOAS algorithm aboard the NASA EOS‐Aura satellite have been used to quantify
the natural spatial variability of TOC over the region of interest as a potential source of
uncertainty in the SPATRAM‐Brewer comparison. Our results show that the differences
observed between both systems is not associated with the natural spatial variability of
TOC. In addition, the OMI‐DOAS total ozone data have been compared to the
ground‐based spectroradiometer data showing an excellent agreement for the Brewer
spectroradiometer (R2 ∼ 0.95) and a fairly good agreement for the SPATRAM instrument
(R2 ∼ 0.89).