Synergy of Using Nadir and Limb Instruments for Tropospheric Ozone Monitoring
Authors: Sofieva Viktoria F. , Hänninen Risto , Sofiev Mikhail , Szelag Monika , Lee Hei Shing , Tamminen Johanna , Retscher Christian 
Published: November 2021

Abstract. The satellite measurements in nadir and limb viewing geometry provide a complementary view of the atmosphere. An effective combination of the limb and nadir measurements can provide a new information about atmospheric composition. In this work, we present tropospheric ozone column datasets that have been created using combination of total ozone column from OMI and TROPOMI with stratospheric ozone column dataset from several available limb-viewing instruments (MLS, OSIRIS, MIPAS, SCIAMACHY, OMPS-LP, GOMOS). We have developed further the methodological aspects of assessment of tropospheric ozone using the residual method using simulations with the chemistry-transport model SILAM. It has been shown that the accurate assessment of ozone in the upper troposphere and the lower stratosphere (UTLS) is of high importance for detecting the ground-level ozone patterns. The stratospheric ozone column is derived from a combination of ozone profiles from several satellite instruments in limb-viewing geometry. We developed a method for the data homogenization, which includes the removal of biases and a-posteriori estimation (validation) of random uncertainties, thus making the data from different instruments compatible with each other. The high horizontal and vertical resolution dataset of ozone profiles is created via interpolation of the limb profiles from each day to 1° × 1° horizonal grid. A new kriging-type interpolation method, which takes into account data uncertainties and the information about natural ozone variations from the SILAM-adjusted ozone field, has been developed. To mitigate the limited accuracy and coverage of the limb profile data in the UTLS, a smooth transition to the model data is applied below the tropopause. This allows estimation of stratospheric ozone column with full coverage of the UTLS. The derived ozone profiles are in very good agreement with collocated ozonesonde measurements. The residual method was successfully applied to OMI and TROPOMI clear-sky total ozone data in combination with the stratospheric ozone column from the high-resolution limb profile dataset. The resulting tropospheric ozone column is in very good agreement with other satellite data. The global distributions of tropospheric ozone exhibit enhancements associated with the regions of high tropospheric ozone production. The main created datasets are (i) monthly 1° × 1° global tropospheric ozone column dataset using OMI and limb instruments, (ii) monthly 1° × 1° global tropospheric ozone column dataset using TROPOMI and limb instruments and (iii) daily 1° × 1° interpolated stratospheric ozone column from limb instruments. Other datasets, which are created as an intermediate step of creating the tropospheric ozone column data, are: (i) daily 1° × 1° clear sky and total ozone column from OMI and TROPOMI (ii) Daily 1° × 1° homogenized and interpolated dataset of ozone profiles and (iii) daily 1° × 1° dataset of ozone profiles from SILAM simulations with adjustment to satellite data. These datasets can be used in various studies related to ozone distributions, variability and trends, both in the troposphere and the stratosphere.