First comparison of OMI‐DOAS total ozone using ground‐based observations at a megacity site in East Asia: Causes of discrepancy and improvement in OMI‐DOAS total ozone during summer

Abstract

This study compares, for the first time, the total ozone columns derived from the Ozone Monitoring Instrument-Differential Optical Absorption Spectroscopy (OMI-DOAS algorithm) (TOCs-OMI) with those obtained from ground-based Brewer and Dobson spectrophotometers (TOCs-Ground) in Seoul, a megacity in northeast Asia, over the 3 years between 2008 and 2010. We found a seasonal mean underestimation of 2.68% (maximum 18.33% on a single day) in TOCs-OMI when compared with TOCs-Ground from Seoul, particularly during the summer seasons (June, July, and August) of our study period: 20 of the 30 days when this underestimation of TOCs-OMI was greatest occurred during the summer. The causes of such large underestimations in summer TOCs-OMI were investigated, and we found that the ghost column densities (GCDs) used in the current OMI-DOAS algorithm did not fully account for the tropospheric ozone amounts below the cloud top in Seoul, particularly during the summer season when surface ozone is enhanced due to active photochemical reactions. We propose the use of New TOCs-OMI based on New GCDs that were calculated using ozonesonde data for the limited number of days when such data were available. The mean bias errors (MBE) against the TOCs-Ground of the New TOCs-OMI and original TOCs-OMI were À0.60% and À2.16%, respectively, which demonstrates the greater accuracy of the New TOCs-OMI. To increase the amount of New TOCs-OMI data available for comparison with the TOCs-Ground data, the regression equation for the relationship between the ozonesonde data and OMI-DOAS cloud pressure data was used to increase the availability of New GCD data for each measurement date that TOCs-OMI data were available for. This procedure reduced the MBE of the original TOCs-OMI by 1.29%, 1.67%, and 1.29% in June, July, and August, respectively. The present study demonstrates that the underestimation of GCDs is one of the major causes of the underestimation of TOCs-OMI during the summer season and suggests that improvements could be achieved using the proposed correction for these GCDs.

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

“…This Dobson was calibrated regularly against the standard instrument, with the most recent one done by NOAA in August-October 2014. The calibration history of this instrument was summarized by Kim et al (2007) and Hong et al (2014), and weekly regular standard lamp and monthly mercury lamp tests have been performed to check radiometric and spectral accuracy, respectively. Because of limitation in observation two to three times per day by the Dobson spectrophotometer (DBS hereafter), the TCO from the DBS has not been available to the diurnal variation of ozone amount.…”

“…However, the ZS-measured TCO is based on the estimation value by the statistical regression approaches by comparing simultaneous observed TCO from DS and ZS under clear-sky conditions. For this reason, DS-measured TCO is more suitable for the comparison test than those from ZS (e.g., Hong et al, 2014;De Backer and De Muer, 1991;Balis et al, 2007). Although the ZS data are partially used from DBS due to its small observation number, the DS data are fully used from BRE for this analysis.…”

“…First, spectral fitting is performed (Platt and Stutz, 2008;Veefkind et al, 2006) to obtain the slant column density (SCD); second, the SCD is converted to the vertical column density (VCD) using the AMF. The final step in the derivation procedure is a correction for the cloud effect (e.g., Hong et al, 2014;McPeters et al, 2008). For the level 3 daily product used in this study, this step consists of gridding and averaging the level 2 TCO orbital swath data onto the 0.25 • × 0.25 • global grids after a quality check.…”

Investigation of SO2Effect on TOMS O3Retrieval from OMI Measurement in China

“…특히 이산화황의 양 이 매우 높게 존재하는 화산 구름 내에서 TOMS 알고리 즘을 이용한 오존 산출에 이산화황이 영향을 주는 것으 로 보고되고 있다 (Krueger, 1983;McPeters et al, 1984;Korean Journal of Remote Sensing, Vol.32, No.6, 2016 -6 30 - Kroon et al, 2008;Choi et al, 2015). 로마, 프랑스, 스페인, 서울에서 이와 같은 유사한 비교 연구가 수행 된 바 있다 (Ialongo et al, 2008;Buchard et al, 2008;Antón et al,, 2009;Hong et al,, 2014). -6 32 - …”

Investigation of SO₂ effect on OMI-TOMS and OMI-DOAS O₃ in volcanic areas with OMI satellite data

“…또한, Differential Optical Absorption Spectroscopy (DOAS) 알고리즘이 위성측정 을 통한 오존 산출에 사용되어 왔다 (Bracher et al, 2005;Kroon et al, 2008;Loyola et al, 2011 (Bracher et al, 2005;Loyola et al, 2011). 현재는 2006 (Kroon et al, 2008 (Ialongo et al, 2008;Buchard et al, 2008;Antón et al, 2009;Hong et al, 2014).…”