Tropospheric ozone and ozone profiles retrieved from GOME-2 and their validation

Abstract

Abstract. This paper describes and assesses the performance of the RAL (Rutherford Appleton Laboratory) ozone profile retrieval scheme for the Global Ozone Monitoring Experiment 2 (GOME-2) with a focus on tropospheric ozone. Developments to the scheme since its application to GOME-1 measurements are outlined. These include the approaches developed to account sufficiently for UV radiometric degradation in the Hartley band and for inadequacies in knowledge of instrumental parameters in the Huggins bands to achieve the high-precision spectral fit required to extract information on tropospheric ozone.The assessment includes a validation against ozonesondes (sondes) sampled worldwide over 2 years (2007)(2008). Standard deviations of the ensemble with respect to the sondes are considerably lower for the retrieved profiles than for the a priori, with the exception of the lowest subcolumn. Once retrieval vertical smoothing (averaging kernels) has been applied to the sonde profiles there is a retrieval bias of 6 % (1.5 DU) in the lower troposphere, with smaller biases in the subcolumns above. The bias in the troposphere varies with latitude. The retrieval underestimates lower tropospheric ozone in the Southern Hemisphere (SH) (15-20 % or ∼ 1-3 DU) and overestimates it in the Northern Hemisphere (NH) (10 % or 2 DU).The ability of the retrieval to reflect the geographical distribution of lower tropospheric ozone, globally (rather than just ozonesonde launch sites) is demonstrated by comparison with the chemistry transport model TOMCAT. For a monthly mean of cloud-cleared GOME-2 pixels, a correlation of 0.66 is found between the retrieval and TOMCAT sampled accordingly, with a bias of 0.7 Dobson Units. GOME-2 estimates higher concentrations in NH pollution centres but lower ozone in the Southern Ocean and South Pacific, which is consistent with the comparison to ozonesondes.

Deriving the slit functions from OMI solar observations and its implications for ozone-profile retrieval

“…However, it is still unclear whether the preflight slit functions adequately represent the on-orbit slit functions for OMI, given the impact of the launching process and the contrasts between laboratory and space conditions. Additionally, the on-orbit slit functions may evolve over time due to instrumental issues, as observed in some other satellite instruments (De Smedt et al, 2012;Miles et al, 2015;Beirle et al, 2017;Sun et al, 2017). The optical degradation of OMI has been markedly small over the mission, but the row anomaly (RA) appeared in 2007 and has made significant impact on about one-third of cross-track positions since January 2009 (Schenkeveld et al, 2017).…”

Seven years of IASI ozone retrievals from FORLI: validation with independent total column and vertical profile measurements

“…The first distributions of tropospheric O 3 were derived from UV-visible (vis) measurements by subtracting an estimate of the stratospheric component from the measured total column (e.g., Fishman and Larsen, 1987;Fishman et al, 1990). More recently, several studies have developed alternative approaches to tropospheric O 3 retrieval from nadirviewing satellite UV spectrometers to have sensitivity to tropospheric O 3 (e.g., Miles et al, 2015;Valks et al, 2014).…”

Quality assessment of the Ozone_cci Climate Research Data Package (release 2017): 2. Ground-based validation of nadir ozone profile data products

“…Each ozone profile is provided in volume-mixing ratio (VMR) and number density (ND) units on a fixed vertical grid with 20 levels ranging between 0 and 80 km, while the values of the 19 intermediate partial ozone column layers are provided as well. The RAL retrieval is a three-step process (Munro et 10 al., 1998;Siddans, 2003;Miles et al, 2015).…”