Surface ozone profiles at selected South Pacific sites

Chandra, Anand; Koshy, Kanayathu; Maata, Matakite

doi:10.1071/sp14008

Cited by 4 publications

(5 citation statements)

References 29 publications

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“…Analysis of 6 years (1997)(1998)(1999)(2000)(2001)(2002)(2003) of data from ozonesondes at four locations in the South Pacific has shown that, for the western Pacific, the seasonal displacement of the South Pacific Convergence Zone (SPCZ) is affecting transport patterns. Both photochemistry and transport patterns control the variability and seasonality in surface O 3 levels (Chandra et al, 2014). On the other hand, O 3 observations at the high-altitude (2.2 km) station of El Tololo in Chile have shown a clear increasing trend from 1995 to 2010 that is strongly related to stratospheric O 3 influx to the troposphere, with maxima in spring that are shifted during recent years to earlier times than before (Anet et al, 2017).…”

Section: Introductionmentioning

confidence: 99%

Impact of biomass burning and stratospheric intrusions in the remote South Pacific Ocean troposphere

et al. 2022

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Abstract. The ozone mixing ratio spatiotemporal variability in the pristine South Pacific Ocean is studied, for the first time, using 21-year-long ozone (O3) records from the entire southern tropical and subtropical Pacific between 1994 and 2014. The analysis considered regional O3 vertical observations from ozonesondes, surface carbon monoxide (CO) observations from flasks, and three-dimensional chemistry-transport model simulations of the global troposphere. Two 21-year-long numerical simulations, with and without biomass burning emissions, were performed to disentangle the importance of biomass burning relative to stratospheric intrusions for ambient ozone levels in the region. Tagged tracers of O3 from the stratosphere and CO from various biomass burning regions have been used to track the impact of these different regions on the southern tropical Pacific O3 and CO levels. Patterns have been analyzed based on atmospheric dynamics variability. Considering the interannual variability in the observations, the model can capture the observed ozone gradients in the troposphere with a positive bias of 7.5 % in the upper troposphere/lower stratosphere (UTLS) as well as near the surface. Remarkably, even the most pristine region of the global ocean is affected by distant biomass burning emissions by convective outflow through the mid and high troposphere and subsequent subsidence over the pristine oceanic region. Therefore, the biomass burning contribution to tropospheric CO levels maximizes in the UTLS. The Southeast Asian open fires have been identified as the major contributing source to CO from biomass burning in the tropical South Pacific, contributing on average for the study period about 8.5 and 13 ppbv of CO at Rapa Nui and Samoa, respectively, at an altitude of around 12 km during the burning season in the spring of the Southern Hemisphere. South America is the second-most important biomass burning source region that influences the study area. Its impact maximizes in the lower troposphere (6.5 ppbv for Rapa Nui and 3.8 ppbv for Samoa). All biomass burning sources contribute about 15–23 ppbv of CO at Rapa Nui and Samoa and account for about 25 % of the total CO in the entire troposphere of the tropical and subtropical South Pacific. This impact is also seen on tropospheric O3, to which biomass burning O3 precursor emissions contribute only a few ppbv during the burning period, while the stratosphere–troposphere exchange is the most important source of O3 for the mid troposphere of the South Pacific Ocean, contributing about 15–20 ppbv in the subtropics.

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Section: Introductionmentioning

confidence: 99%

Impact of biomass burning and stratospheric intrusions in the remote South Pacific Ocean troposphere

et al. 2022

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show abstract

“…Analysis of 6-years (1997-2003) of data from ozonesondes at four locations in the south Pacific has shown that, for the Western Pacific, the seasonal displacement of the South Pacific Convergence Zone (SPCZ) is affecting transport patterns. Both photochemistry and transport patterns control the variability and seasonality in surface O3 levels (Chandra et al, 2014). On the other hand, O3 observations at high altitude (2.2. km) station of El Tololo in Chile have shown a clear increasing trend from 1995 to 2010 that is strongly related with stratospheric O3 influx to the troposphere, with maxima in spring that are shifted during recent years to earlier times than before (Anet et al, 2017).…”

Section: Introductionmentioning

confidence: 99%

Impact of biomass burning and stratospheric intrusions in the remote South Pacific Ocean troposphere

Daskalakis

Gallardo

Kanakidou

et al. 2021

Preprint

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Abstract. The ozone mixing ratio spatio-temporal variability in the pristine southern Pacific Ocean is studied, for the first time, using 21-year long ozone (O3) records from the entire southern tropical and subtropical Pacific, between 1994 and 2014. The analysis considered regional O3 vertical observations from ozonesondes, surface carbon monoxide (CO) observations from flasks and three-dimensional chemistry-transport model simulations of the global troposphere. Two 21-year long numerical simulations, with and without biomass burning emissions, were performed to disentangle the importance of biomass burning relative to stratospheric intrusions for ambient ozone levels in the region. Tagged tracers of O3 from the stratosphere and CO from various biomass burning regions have been used to track the impact of these different regions on the southern tropical Pacific O3 and CO levels. Patterns have been analyzed based on atmospheric dynamics variability. Considering the interannual variability in the observations, the model can capture the observed ozone gradients in the troposphere with a positive bias of 7.5 % in the upper troposphere/low stratosphere (UTLS), as well as near the surface. Remarkably, even the most pristine region of the global ocean is affected by distant biomass burning emissions by convective outflow through the mid and high troposphere and subsequent subsidence over the pristine oceanic region. Therefore, the biomass burning contribution to tropospheric CO levels maximizes in the UTLS. The Southeast Asian open fires have been identified as the major contributing source to CO from biomass burning in the tropical southern Pacific, contributing on average for the study period about 8.5 and 13 ppbv of CO at Rapa Nui and Samoa, respectively, at an altitude of around 12 km during the burning season in the spring of the Southern Hemisphere. South America is the second most important biomass burning source region that influences the study area. Its impact maximizes in the lower troposphere (6.5 ppbv for Rapa Nui and 3.8 ppbv for Samoa). All biomass burning sources contribute about 15–23 ppbv of CO, accounting for about 25 % of the total CO in the entire troposphere of the tropical and subtropical South Pacific. This impact is also seen on tropospheric O3, to which biomass burning O3 precursor emissions contribute only a few ppbv during the burning period, while the stratosphere-troposphere exchange is the most important source of O3 for the mid-troposphere of the south Pacific Ocean, contributing about 15–20 ppbv in the subtropics.

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“…Advection from the southern mid-latitudes introduces upper tropospheric and stratospheric ozone, along with emissions resulting from biomass burning. Being south of SPCZ, Fiji is more exposed to the latter (Chandra et al, 2014). According to Oltmans et al (2001), the impact of African wildfires is also prominent after August (Fig.…”

mentioning

confidence: 97%

“…8i). Moreover, the South Pacific Convergence Zone (SPCZ) nearby brings clean marine air to the upper troposphere (Chandra et al, 2014).…”

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confidence: 99%

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Improved CCD tropospheric ozone from S5P TROPOMI satellite data using local cloud fields

Maratt Satheesan,

Eichmann,

Burrows

et al. 2024

Preprint

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Abstract. We present the CHORA (Cloud Height Ozone Reference Algorithm) algorithm for retrieving tropospheric ozone columns from S5P/TROPOMI. The method uses a local cloud reference sector (CLC, CHORA Local Cloud) to determine the stratospheric (above cloud) column, which is subtracted from the total column in clear-sky scenes in the same zonal band to retrieve the tropospheric column. The standard CCD (Convective Cloud Differential) approach uses cloud data from the Pacific region (CPC, CHORA Pacific Cloud) instead. An important assumption for the standard method is the zonal invariance of stratospheric ozone. The local cloud approach is the first step to diminish this constraint in order to extend the CCD method to middle latitudes, where stratospheric ozone variability is larger. An iterative approach has been developed for the automatic selection of an optimal local cloud reference sector around each retrieval grid box varying longitudinally between ±5° and ±50° and latitudinally by ±1°. The optimised CLCT (CHORA-Local Cloud Theil-Sen algorithm) algorithm, a follow-up from CLC, employs a homogeneity criterion for total ozone from the cloud reference sector in order to overcome the inhomogeneities in stratospheric ozone. It directly estimates the above cloud column ozone for a common reference altitude of 270 hPa using the Theil-Sen regression. The latter allows combining the CCD method with the cloud slicing algorithm that retrieves upper tropospheric ozone volume mixing ratios. Monthly averaged Tropospheric Column Ozone (TCO) using the Pacific cloud reference sector (CPC) and local cloud reference sector (CLC, CLCT) have been determined over the tropics and subtropics (26° S–21° N) from TROPOMI for the time period from 2018 to 2022. The accuracy of the various methods was investigated by comparisons with collocated NASA/GSFC SHADOZ ozonesonde measurements and the ESA TROPOMI Level 2 tropospheric ozone product. At eleven out of twelve stations, tropospheric ozone columns using CLCT yield better agreement with ozonesondes than CPC. The overall statistical dispersion is effectively reduced from 4 DU (CPC) to 2 DU (CLCT). In the tropical region (20° S–20° N), CLCT shows a significantly lower overall mean bias and dispersion of -1±8 %, outperforming both CPC (12±9 %) and CCD-ESA (22±10 %). CLCT surpasses the ESA operational product, providing more accurate tropospheric ozone retrievals at eight out of nine stations in the tropics. For the Hilo station, with a larger stratospheric ozone variability due to its proximity to the subtropics, the bias of +25 % (CPC) is effectively reduced to -12 % (CLCT). Similarly, in the subtropics (Reunion, Irene, and Hanoi), the CLCT algorithm provides an improved overall bias and scatter (-11±8 %) compared to CPC (-17±13 %) with respect to sondes but the bias remains negative. The CLCT effectively reduces the impact of stratospheric ozone inhomogeneity, typically at higher latitudes. These results demonstrate the advantage of the local cloud reference sector in the subtropics. The algorithm, thereby, is an important basis for subsequent systematic applications in current and future missions of geostationary satellites, like GEMS (Geostationary Environment Monitoring Spectrometer, Korea), ESA Sentinel-4, and NASA TEMPO (Tropospheric Emissions: Monitoring of POllution) covering predominantly middle latitudes.

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Surface ozone profiles at selected South Pacific sites

Abstract: Surface ozone profiles were studied at Fiji (18

Cited by 4 publications

References 29 publications

Impact of biomass burning and stratospheric intrusions in the remote South Pacific Ocean troposphere

Impact of biomass burning and stratospheric intrusions in the remote South Pacific Ocean troposphere

Impact of biomass burning and stratospheric intrusions in the remote South Pacific Ocean troposphere

Improved CCD tropospheric ozone from S5P TROPOMI satellite data using local cloud fields

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