Characterizing ozone throughout the atmospheric column over the tropical Andes from in situ and remote sensing observations

Abstract

In this study, we characterize atmospheric ozone over the tropical Andes in the boundary layer, the free troposphere, and the stratosphere; we quantify each contribution to total column ozone, and we evaluate the performance of the multi-sensor reanalysis (MSR2) in the region. Thus, we present data taken in Ecuador and Peru (2014–2019). The contribution from the surface was determined by integrating ozone concentrations measured in Quito and Cuenca (Ecuador) up to boundary layer height. In addition, tropospheric and stratospheric column ozone were quantified from ozone soundings (38) launched from Quito during the study time period. Profiles were compared against soundings at Natal (SHADOZ network) for being the closest observational reference with sufficient data in 2014–2019. Data were also compared against stratospheric mixing ratios from the Aura Microwave Limb Sounder (Aura MLS). Findings demonstrate that the stratospheric component of total column ozone over the Andes (225.2 ± 8.9 Dobson Units [DU]) is at similar levels as those observed at Natal (223.3 ± 8.6 DU), and observations are comparable to Aura MLS data. In contrast, the tropospheric contribution is lower over the Andes (20.2 ± 4.3 DU) when compared to Natal (35.4 ± 6.4 DU) due to a less deep and cleaner troposphere. From sounding extrapolation of Quito profiles down to sea level, we determined that altitude deducts about 5–7 DU from the total column, which coincides with a 3%–4% overestimation of the MSR2 over Quito and Marcapomacocha (Peru). In addition, when MSR2 data are compared along a transect that crosses from the Amazon over Quito, the Ecuadorian coast side, and into the Pacific, observations are not significantly different among the three first locations. Results point to coarse reanalysis resolution not being suitable to resolve the formidable altitude transition imposed by the Andes mountain chain. This work advances our knowledge of atmospheric ozone over the study region and provides a robust time series of upper air measurements for future evaluations of satellite and reanalysis products.

An ozonesonde evaluation of spaceborne observations in the Andean tropics

“…However, ozone climatologies use profiles from sites mostly at the sea level in the Atlantic and Pacific basins, while profiles at high altitude in the tropical Andes deviate from those locations mainly in the troposphere. Thus, previous research demonstrates significant differences in profile structure and in the magnitude of TrCO (lower) from stations in Galapagos (Ecuador) and Natal (Brazil), while stratospheric ozone is similar and consistent with Microwave Limb Sounder (MLS/Aura) measurements 12 , 13 . Hence, we compared mean differences in TCO, TrCO, and stratospheric column ozone (SCO) between Ziemke’s climatology and the compendium of EMA’s observations in Quito (Table S1 ).…”

“…However, from high resolution profiles, the Andean tropical troposphere is located at 96 hPa (17 ± 0.7 km) (see “ Methods ” section, Table S2 ). Moreover, previous work demonstrates that the tropopause level identified with the chemical definition (“ Methods ” section) mostly coincides with the coldest point in the temperature profile 13 . This indicates that, unlike sites in the Pacific and Atlantic 23 , 24 , ozone at the Andean tropics is generally well-mixed up to tropopause level.…”

“…4 a,b). Previous research shows that tropospheric ozone in the tropical Andes is low as altitude deducts 5–7 DU from the TrCO, while ozone from the boundary layer is also low 13 . However, TROPOMI/S5P measures generally higher values even though observations correspond to a fraction of the column.…”

“…Table S2 provides details of ozonesonde launch date, time, turn altitude and pressure, as well as ozone column measurements determined with the same methodology followed in previous work 12 , 13 . Thus, TCO was obtained by integrating ozone up to balloon burst altitude and adding the SBUV climatology extrapolation by McPeters and Labow 19 (add-on table available at https://acd-ext.gsfc.nasa.gov/anonftp/toms/ ).…”

“…In situ sampling of ozone on board of high-altitude balloons began actively in 2014 at Universidad San Francisco de Quito’s Atmospheric Measurement Station (EMA, Spanish acronym) in Ecuador 12 , 13 . This effort continued into 2021 with the support of the Vienna Convention Trust Fund (VCTF).…”