Evaluation of Version 3 Total and Tropospheric Ozone Columns From Earth Polychromatic Imaging Camera on Deep Space Climate Observatory for Studying Regional Scale Ozone Variations

Abstract

Discrete wavelength radiance measurements from the Deep Space Climate Observatory (DSCOVR) Earth Polychromatic Imaging Camera (EPIC) allows derivation of global synoptic maps of total and tropospheric ozone columns every hour during Northern Hemisphere (NH) Summer or 2 hours during Northern Hemisphere winter. In this study, we present version 3 retrieval of Earth Polychromatic Imaging Camera ozone that covers the period from June 2015 to the present with improved geolocation, calibration, and algorithmic updates. The accuracy of total and tropospheric ozone measurements from EPIC have been evaluated using correlative satellite and ground-based total and tropospheric ozone measurements at time scales from daily averages to monthly means. The comparisons show good agreement with increased differences at high latitudes. The agreement improves if we only accept retrievals derived from the EPIC 317 nm triplet and limit solar zenith and satellite looking angles to 70°. With such filtering in place, the comparisons of EPIC total column ozone retrievals with correlative satellite and ground-based data show mean differences within ±5-7 Dobson Units (or 1.5–2.5%). The biases with other satellite instruments tend to be mostly negative in the Southern Hemisphere while there are no clear latitudinal patterns in ground-based comparisons. Evaluation of the EPIC ozone time series at different ground-based stations with the correlative ground-based and satellite instruments and ozonesondes demonstrated good consistency in capturing ozone variations at daily, weekly and monthly scales with a persistently high correlation (r2 > 0.9) for total and tropospheric columns. We examined EPIC tropospheric ozone columns by comparing with ozonesondes at 12 stations and found that differences in tropospheric column ozone are within ±2.5 DU (or ∼±10%) after removing a constant 3 DU offset at all stations between EPIC and sondes. The analysis of the time series of zonally averaged EPIC tropospheric ozone revealed a statistically significant drop of ∼2–4 DU (∼5–10%) over the entire NH in spring and summer of 2020. This drop in tropospheric ozone is partially related to the unprecedented Arctic stratospheric ozone losses in winter-spring 2019/2020 and reductions in ozone precursor pollutants due to the COVID-19 pandemic.

NASA Satellite Measurements Show Global‐Scale Reductions in Free Tropospheric Ozone in 2020 and Again in 2021 During COVID‐19

“…We did not find any clear connection in the SH between TCO decreases and negative anomalies in either NO 2 or smoke aerosols (Figure S11 in Supporting Information S1 ). The decreases of TCO in the SH in 2020–2021 may have been related to anomalies in STE in the presence of a strong and long‐lasting Antarctic polar vortex in the SH in October‐December 2020 that resulted in substantial stratospheric ozone loss (Kramarova, Newman, et al., 2021 ; Kramarova, Ziemke, et al., 2021 ; Stone et al., 2021 ); however, establishing such a connection requires modeling and is beyond the scope of our study.…”

“…( 2021 ), Kramarova, Ziemke, et al. ( 2021 ) showed anomalous decreases in zonal‐mean tropospheric column ozone (TCO) throughout the NH extra‐tropics of about 2–4 Dobson Units (DU) (5%–10%) in spring‐summer 2020. Elshorbany et al.…”

“…All TCO datasets represent daily global maps (outside polar night regions) at 1° latitude × 1° longitude gridding. Details regarding individual TCO measurements for EPIC, OMPS, and OMI with MERRA-2 SCO are discussed byKramarova, Newman, et al (2021),Kramarova, Ziemke, et al (2021) andElshorbany et al (…”

“…Bouarar et al (2021) used a model simulation to indicate 5%-15% reductions of NH zonally averaged ozone in the free troposphere in winter-spring 2020; they attributed about 1/3 coming from reduction of air traffic, 1/3 from reduction in surface emissions, and 1/3 from meteorological conditions that includes the 2020 Arctic stratospheric ozone depletion. Using satellite data from the Earth Polychromatic Imaging Camera (EPIC) instrument, Kramarova, Newman, et al (2021), Kramarova, Ziemke, et al (2021) showed anomalous decreases in zonal-mean tropospheric column ozone (TCO) throughout the NH extra-tropics of about 2-4 Dobson Units (DU) (5%-10%) in spring-summer 2020. Elshorbany et al (2021) also described reductions of several percent in tropospheric ozone over the continental US using the Ozone Mapping and Profiler Suite (OMPS) satellite data.…”

An approach to track instrument calibration and produce consistent products with the version-8 total column ozone algorithm (V8TOZ)

“…Since then, instruments for ozone observations have been available on various platforms. Some of these instruments are the Global Ozone Monitoring Experiment (GOME) on board the European Remote Satellite-2 (ERS-2) (Bodeker et al, 2001), the Ozone Monitoring Instrument (OMI) on board the Earth Observation System Aura satellite (Koukouli et al, 2012), the Earth Polychromatic Imaging Camera (EPIC) on board the NOAA Deep Space Climate Observatory (DSCOVR) spacecraft Kramarova et al, 2021), and the TROPOspheric Monitoring Instrument (TROPOMI) on board the Sentinel-5 Precursor (S5P) mission (Lindfors et al, 2018;Inness et al, 2019;Garane et al, 2019). The concept of the UV-absorbing aerosol index (AI) was initially introduced in the context of observations made Z.…”