Limb–nadir matching using non-coincident NO<sub>2</sub> observations: proof of concept and the OMI-minus-OSIRIS prototype product

Abstract

Abstract. A variant of the limb-nadir matching technique for deriving tropospheric NO 2 columns is presented in which the stratospheric component of the NO 2 slant column density (SCD) measured by the Ozone Monitoring Instrument (OMI) is removed using non-coincident profiles from the Optical Spectrograph and InfraRed Imaging System (OSIRIS). In order to correct their mismatch in local time and the diurnal variation of stratospheric NO 2 , OSIRIS profiles, which were measured just after sunrise, were mapped to the local time of OMI observations using a photochemical box model. Following the profile time adjustment, OSIRIS NO 2 stratospheric vertical column densities (VCDs) were calculated. For profiles that did not reach down to the tropopause, VCDs were adjusted using the photochemical model. Using air mass factors from the OMI Standard Product (SP), a new tropospheric NO 2 VCD product -referred to as OMI-minus-OSIRIS (OmO) -was generated through limb-nadir matching. To accomplish this, the OMI total SCDs were scaled using correction factors derived from the next-generation SCDs that improve upon the spectral fitting used for the current operational products. One year, 2008, of OmO was generated for 60 • S to 60 • N and a cursory evaluation was performed. The OmO product was found to capture the main features of tropospheric NO 2 , including a background value of about 0.3 × 10 15 molecules cm −2 over the tropical Pacific and values comparable to the OMI operational products over anthropogenic source areas. While additional study is required, these results suggest that a limb-nadir matching approach is feasible for the removal of stratospheric NO 2 measured by a polar orbiter from a nadir-viewing instrument in a geostationary orbit such as Tropospheric Emissions: Monitoring of Pollution (TEMPO) or Sentinel-4.

The Ozone Monitoring Instrument: overview of 14 years in space

“…These OMI data products include near UV (OMAERUV) aerosol record of AOD, single scattering albedo (SSA) and aerosol index (AI; Torres et al, 2007). Retrieved AOD and SSA products have been evaluated using ground-based observations (Ahn et al, 2014;Jethva et al, 2014a) as well as other satellite-based products (Ahn et al, 2008;Gasso and Torres, 2016). OMAERUV observations of aerosol UV absorption spectral dependence are being used to improve tropospheric photochemistry modeling capabilities (X. .…”

“…Joint analysis of stratospheric NO 2 measured by the Odin/OSIRIS limb viewing instrument (Haley and Brohede, 2007) and OMI column NO 2 to improve the tropospheric NO 2 column have been demonstrated by Adams et al (2016) by analyzing 1 year of data from OSIRIS along with a photochemical box model to account for diurnal variations of stratospheric NO 2 and the temporal mismatch in observations. The authors conclude that in order to fully exploit the advantage of the methodology, further work is needed to understand all biases between the instruments.…”

Validation of MAX-DOAS retrievals of aerosol extinction, SO<sub>2</sub>, and NO<sub>2</sub> through comparison with lidar, sun photometer, active DOAS, and aircraft measurements in the Athabasca oil sands region

“…S ratios were modelled using Mie scattering theory and measurements of surface-level particle composition and size distribution at Fort McKay South for various times during 23 August to determine temporal variability in the S ratio. Source code for the Mie scattering calculations can be found in Aggarwal et al (2018).…”

“…Forest fire smoke has been observed above the boundary layer by airborne lidar measurements in AOSR (see Figs. 12 and 13 and discussion of elevated forest fire plumes in Aggarwal et al, 2018). Therefore, the aerosol extinction above the boundary layer in the AOSR could contribute to a significant fraction of the total atmospheric AOD on certain days depending on the emission and transport of aerosols.…”

The Ozone Monitoring Instrument: Overview of twelve years in space

“…In addition to the work using multiple sensors with OMI to provide information on tropospheric ozone (see Sect. 7.3), Adams et al (2016) have applied a variant of the limb-nadir matching technique for deriving tropospheric NO 2 columns from a combination of non-coincident profiles from the Optical Spectrograph and InfraRed…”