A Comparison of MICROTOPS II and OMI Satellite Ozone Measurements in Novi Sad from 2007 to 2015 Z. PODRASCANIN, 1 I. BALOG, 1 A. JANKOVIC, 2 Z. MIJATOVIC, 1 and Z. NADJ 1 Abstract—In this paper, we present consecutive daily mea- surements of the total ozone column (TOC) using MICROTOPS II in Novi Sad, the Republic of Serbia (45.3 N, 19.8 E and the altitude of 84 m) from 2007 to 2015. The MICROTOPS II data set was compared to the ozone monitoring instrument (OMI) satellite data, since there was no nearby comparative long-time series available for the Dobson or Brewer instrument. The data quality control of the measured MICROTOPS II TOC data was carried out before the comparison with the satellite data. The MICROTOPS II was cali- brated at the manufacturer’s facilities and only TOC values drawn from the 305.5/312.5 nm wavelength combination were compared with the satellite data. The mean bias deviation between MICROTOPS II and OMI satellite data sets was obtained to be less than 2%, and the mean absolute deviation was in the range of 5%. The difference in the mean seasonal TOC values in summer and autumn was less than 0.5%, while in winter and spring this dif- ference reached 2.8%. A possible calibration of MICROTOPS II instrument with the satellite data is presented, where the calibration coefficients for all channels were calculated for every satellite and MICROTPS II data pair during one year. Then, the average value of all the calculated coefficients was used for instrument calibra- tion. The presented calibration improves the MICROTOPS II instrument stability and enables the usage of all the wavelength combinations. Key words: Total ozone column (TOC), MICROTOPS II, satellite measurements, OMI, instrument calibration. 1. Introduction The ozone distribution in the stratosphere has spatial and temporal variability all over the globe (Bowman and Krueger 1985; Bowman 1989; Wespes et al. 2016). The monitoring of stratospheric ozone is necessary to understand atmospheric chemistry and to follow recovery of stratospheric ozone, which is expected to happen throughout the 21st century (WMO 2011). The monitoring of the total ozone column (TOC) in the atmosphere could be conducted using (1) ground-based, and (2) satellite measure- ments. Dobson (1931) and Brewer (1973) spectrophotometers are set as reference instruments for ground-based TOC measurements. Both instru- ments are accurate and reliable but also quite expensive and complex for maintenance (Balis at el. 2007). As an alternative, a cheap, portable and easy to use instrument, MICROTOPS II (Morys et al. 2001), could be a suitable choice. This instrument is a filter sun photometer, and it is a very good solution for monitoring TOC (Ko ¨hler 1999; Morys et al. 2001). The use of this instrument spread the monitoring network of TOC in developing countries. To perceive the pros and cons of MICROTOPS II regarding standard Dobson and Brewer spectropho- tometers, various scientists compared measurements obtained by these instruments. Two-year measure- ments obtained in Hohrnpriddrnberg using this instrument were compared to regular spectrometers Dobson No. 104 and Brewer No. 10 and the inter- comparison was also done with a standard Dobson No. 065 and 064. The comparison showed that the differences between instruments at airmass lower than 3.5 were mostly less than ±2%. When the air- mass increases, the differences between TOC values measured with MICROTOPS II, Dobson and Brewer spectrometers, also increases (Ko ¨hler 1999). In their 6 field campaigns, Go ´mez-Amo et al. (2012) showed that the MICROTOPS II was stable during 10 years in comparison with a Brewer spectrometer when the airmass limit was fixed to 3 considering various 1 Department of Physics, Faculty of Sciences, University of Novi Sad, Novi Sad, Republic of Serbia. E-mail: zorica.podrascanin@df.uns.ac.rs 2 Faculty of Architecture, Civil Engineering and Geodesy, University of Banja Luka, Banja Luka, Bosnia and Herzegovina. Pure Appl. Geophys. Ó 2017 Springer International Publishing AG DOI 10.1007/s00024-017-1665-0 Pure and Applied Geophysics