Synergy of Using Nadir and Limb Instruments for Tropospheric Ozone Monitoring (SUNLIT)
Authors: Sofieva Viktoria F. , Hänninen Risto , Sofiev Mikhail , Szeląg Monika , Lee Hei Shing , Tamminen Johanna , Retscher Christian 
Published: May 2022

Abstract. 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 give new information about atmospheric
composition. In this work, we present tropospheric ozone column datasets
that have been created using a combination of total ozone columns from OMI (Ozone Monitoring Instrument) and
TROPOMI (TROPOspheric Monitoring Instrument) with stratospheric ozone column datasets from several available
limb-viewing instruments: MLS (Microwave Limb Sounder), OSIRIS (Optical Spectrograph and InfraRed
Imaging System), MIPAS (Michelson Interferometer for Passive Atmospheric Sounding), SCIAMACHY (SCanning Imaging Spectrometer for Atmospheric CHartographY), OMPS-LP (Ozone Mapping and Profiles
Suite – Limb Profiler), and GOMOS (Global Ozone Monitoring by Occultation of Stars). We have developed further the methodological aspects of the assessment of
tropospheric ozone using the residual method supported by simulations with
the chemistry transport model SILAM (System for Integrated modeLling of Atmospheric coMposition). 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 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 a 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 for the estimation of the 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
developed 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 datasets created are (i) a monthly 1∘×1∘ global tropospheric ozone column dataset (from ground to 3 km below the tropopause) using OMI and limb instruments, (ii) a monthly 1∘×1∘ global tropospheric ozone column dataset using TROPOMI and limb instruments, and (iii) a 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) a daily 1∘×1∘ clear-sky and total ozone column from OMI and TROPOMI, (ii) a daily 1∘×1∘ homogenized and interpolated dataset of ozone profiles from limb instruments, and (iii) a 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 variability and trends in ozone distributions in both the troposphere and the
stratosphere. The datasets are processed from the beginning of OMI and
TROPOMI measurements until December 2020 and are planned to be regularly
extended in the future.