Paper Title
Comparing OMI-TOMS and OMI-DOAS Ozone Columns over Volcanic Site and Chinese Industrial Region

Abstract
In this present study, we identified the SO2 effect on O3 retrieval from the Ozone Monitoring Instrument (OMI) measurement over volcanic sites including Anatahan, La Cumbre, Sierra Negra, and Piton and over Chinese industrial region from 2005 to 2008. In volcanic plumes, OMI-Total Ozone Mapping Spectrometer (TOMS) total O3 column increases with middle and upper troposphere and stratosphere (TRM-STL) SO2, showing high correlation (R = 0.54) between TRM-STL SO2 and TOMS O3 while there is negligible correlation (R = 0.11) between TRM-STL SO2 and OMI-Differential Optical Absorption Spectrometer (DOAS) O3. TRM-STL SO2 and the difference between OMI-TOMS and OMI-DOAS O3 (T−D) are well correlated (R = 0.54) and maximum T−D reaches to 90 DU. Although T−D in the Chinese industrial region increases more slowly with SO2 than those at the volcanic sites, T−D has a dependence on planetary boundary layer (PBL) SO2 (R = 0.36). Thus, the altitude at which SO2 exists has an effect on T−D, which could be due to reduced absolute radiance sensitivity in the boundary layer at 317.5 nm (the wavelength used to retrieve OMI-TOMS ozone in boundary layer).In terms of evaluating seasonal characteristics of T−D, it also represent that T−D have dependence on PBL SO2. In Turkey (average PBL SO2 = 0.6 DU) and West USA (average PBL SO2 = 0.5 DU) which shows low SO2 condition, there is an explicit seasonal variation in T−Dby showing its maximum in summer and minimum in winter. However, there is no specific seasonal variation in T−D in Chinese industrial region (PBL SO2 = 1.1 DU) by showing higher T−D and SO2 amount than those in Turkey and West USA. In this present study, we discussed the reason for the seasonal characteristic of T−D in Chinese industrial region. In addition, the effect of AOD and SZA is investigated for their effects on the relationship between PBL SO2 and T−D.