A pivotal study led by Professor Jayanarayanan Kuttippurath from IIT Kharagpur, in collaboration with international researchers, confirms there is no ozone hole in the tropical stratosphere. This significant finding, detailed in the study “No Severe Ozone Depletion in the Tropical Stratosphere in Recent Decades,” utilizes extensive data from ground-based ozonesondes and satellites over five decades (1980–2022).
Contrary to previous claims, the research shows no substantial ozone depletion in the tropics, with average ozone levels well above the critical threshold, thereby alleviating fears about potential health risks to millions residing in tropical regions. This reassurance is supported by a robust analysis indicating that any observed fluctuations in ozone are due to atmospheric dynamics, not chemical depletion, confirming that ozone depletion remains predominantly a polar phenomenon restricted to Antarctica.
Here is the Summary of the Study:
– Ozone, a triatomic molecule, makes up 90% of its atmospheric abundance in the stratosphere, located from roughly 10 to 50 km above the ground.
– Stratospheric ozone is chemically produced in the tropical stratosphere around 25–35 km and then transported to the middle and high latitudes.
Ozone Patterns:
– Ozone mixing ratios are highest in the tropics and decrease towards the polar regions. Ozone column amount increases with latitude towards the poles.
– A decrease in ozone concentration would lead to more UV radiation reaching the Earth’s surface, posing a significant threat to life.
Ozone Depletion:
– Ozone depletion in the Antarctic lower stratosphere is significant due to anthropogenic halogens, leading to concerns about UV-B radiation’s impact on life.
– Ozone loss is severe due to unusual meteorology and isolation of mid-latitude air from polar air.
Recent Trends:
– The reduction in stratospheric halogens has contributed to the steady increase in ozone levels since the 2000s.
– Lower-stratospheric ozone in both the mid-latitudes and the tropics has seen a 1%–3% per decade reduction since 2000.
Observations:
– Observational evidence does not support the possibility of an ozone hole occurring outside Antarctica with respect to present-day stratospheric halogen levels.
– No observational evidence found regarding severe stratospheric ozone depletion in the tropics, in contrast to recent claims.
Conclusion:
– The analysis indicates no severe stratospheric ozone depletion in the tropics in the recent decades.
– Current understanding and observational evidence do not provide support for the possibility of an ozone hole occurring outside Antarctica today.
Trends in Ozone Depletion:
– Ozone loss in the tropics is minimal compared to the mid-latitudes, with insignificant trends in available analyses.
– Recent claims of severe ozone depletion in the tropical stratosphere have been refuted due to lack of robust observational evidence.
Data Sources:
– GOZCARDS v2.2 provides bias-corrected merged satellite-based ozone data from 1979 to 2018, suitable for global trend analysis.
– SWOOSH version 2 is a merged dataset of ozone mixing ratios from different limb-sounding satellite instruments.
Satellite-Based Ozone Data:
– SBUV Merged Ozone Dataset offers a long-term record of ozone profiles and TCO from 1970 to 2013.
– The GSG TCO dataset combines measurements from multiple satellite instruments for improved coverage since 1995.
Ozonesonde Data:
– SHADOZ project measures ozone vertical profiles using ozonesondes in the Southern Hemisphere.
– WOUDC ECC ozonesonde data, with high accuracy and precision, is utilized for ozone measurements since 1980.
Observations and Challenges:
– Observational and reprocessed ozone data challenge claims of significant tropical ozone depletion.
– Tropical stratospheric ozone depletion hypotheses lack support from satellite and CFC-12 data.
TOST Dataset:
– Global three-dimensional height-resolved ozone dataset derived from WOUDC records.
– Spatially interpolated using 96h trajectories calculated using HYSPLIT model.
TROPOMI Ozone Data:
– Utilizes UV and visible bands to capture ozone absorption features.
– High spatial resolution of 7×5 km provides precise TCO measurements.
OMPS Ozone Data:
– Measures TCO using backscattered solar radiances with a negative bias of 2%-4%.
– Swath area approximately 50×2800 km2 with high spectral resolution.
OMI Ozone Instrument:
– Uses UV and visible spectrometry techniques for accurate TCO measurements.
– High spatial resolution of 25×25 km with bias <6% in tropics and mid-latitudes.
TOMS Ozone Measurements:
– Instruments aboard Nimbus-7 and Earth Probe measure TCO.
– Utilizes single monochromator and scanning mirror with uncertainties of about 3.3%.
Ozone Trend Analysis:
– Long-term trends estimated using linear method and multiple linear regression model.
– Includes explanatory variables like ENSO, QBO, solar cycle, and aerosol optical depth.
Ozone Variability:
– High ozone in tropics (10-11 ppm) decreasing towards high latitudes (2-5 ppm).
– Seasonal averages show high ozone in summer, lower in autumn and winter.
Latitudinal Distribution of Ozone:
– Seasonal variability higher in polar regions with respect to latitudinal distribution of sunlight.
– Smaller wintertime ozone values in polar lower stratosphere indicate seasonal ozone loss.
Seasonal Distribution of Total Column Ozone (TCO) in 2015:
– High TCO in northern high latitudes during winter and spring
– Low TCO in the Southern Hemisphere (SH) spring
Changes in TCO Over the Tropics (1978-2022):
– Peak TCO decrease during 1995-1999 followed by an increase post-1997
– Consistent TCO levels across datasets with minimal bias
Trends in Tropical Ozone (1979-2022):
– Negative trends in satellite-based estimates pre- and post-1997
– Non-significant trends in reanalysis data
Stratospheric Ozone Trends (1984-2022):
– Non-significant trends in ozone at most altitudes
– Differing positive and negative trends in different periods
Comparison of SWOOSH and GOZCARDS Ozone Data:
– Similar trends with slight differences in upper and middle stratosphere
– Good agreement in lower and upper stratosphere post-2004
Substantial Ozone Loss During 1984-1997 Period:
– Consistent ozone loss at all latitudes and seasons
– Neutral ozone trends in the tropics
Questioning the Concept of a Tropical Ozone Hole:
– Concerns raised about claims of a tropical “ozone hole”
– Data inconsistencies and doubts regarding the study by Lu (2022)
Data Gaps in Tropical Ozone Studies:
– Significant data gaps observed in tropical ozone studies, especially in the tropics from 1960 to 1980.
– TOST data in the tropics have very low ozone values, hampering statistical analysis.
Low-Ozone-Value Region in Tropical Stratosphere:
– Long-known issue of low ozone values in tropical stratosphere due to BDC’s upwelling branch.
– Ozonesonde measurements in the tropics show small ozone values in lower stratosphere.
Trends in Tropical Ozone Concentrations:
– Decadal changes in tropical ozone concentrations marginal over the past 4 decades.
– MLR method applied to SWOOSH and GOZCARDS data show declining ozone trend in upper stratosphere.
Comparison of TOST and SHADOZ Data:
– Bias observed in TOST data compared to SHADOZ data in the tropics.
– TOST data show low bias below 20 km but higher bias above.
Ozone Hole Definition Issues:
– Critique on using percentage change to define ‘ozone hole’ instead of absolute ozone values.
– Ozone hole impact should be based on the absolute amount of ozone in the region.
TCO Levels and Altitude Misrepresentation:
– TCO never below 220 DU in the tropics post-2005.
– Incorrect assignment of tropical altitudes by Lu in stratosphere-troposphere division.
Absence of Polar Vortex and PSCs in Tropical Ozone Loss:
– No evidence of polar vortices or PSCs in tropical ozone loss mechanisms.
– Absence of ice particles in tropical stratosphere contradicts CRE theory proposed by Lu.
Historical Trends in Tropical Stratospheric Ozone:
– Previous studies highlighted minimal or absent trends in tropical stratospheric ozone from 1979 to 1997.
– Lack of acknowledgment of historical data in recent studies.
Issue with Lu’s Claim on Tropical Ozone Loss:
– The TOST data used by Lu (2022) are sparse in tropical latitudes, making scientific claims with interpolated data unreliable.
– Contrary to Lu’s assertion, independent datasets show a slight increase or no significant change in tropical stratospheric ozone over the past decades.
Factors Affecting Tropical Ozone Levels:
– Changes in the Brewer-Dobson Circulation (BDC) dynamics contribute to ozone variations in the tropical stratosphere.
– Enhanced transport of ozone to middle latitudes and increased emissions of halogen-containing species and aerosols are factors lowering tropical ozone.
Potential Decline in Tropical Ozone:
– The motion of air in the tropics shortens the time for ozone production, while other factors like changing solar activity may further reduce tropical ozone in the future.
Misrepresentation in Lu’s Analysis:
– Lu’s study neglects the major portion of tropical ozone due to focusing on lower stratospheric values, leading to an inaccurate portrayal of ozone levels.
– Claims of a ‘tropical ozone hole’ and associated threats are unfounded and primarily due to flawed data interpretation.
Consistent Picture of Tropical Ozone Evolution:
– Contrary to Lu’s claim, recent analyses show no significant decrease or increase in tropical stratospheric ozone, with negative trends possibly linked to dynamic processes.
Sole Reliance on Limited Dataset by Lu (2022):
– Lu’s conclusions are based on a narrow decadal dataset with limited profiles, while broader analyses using diverse data sources depict a different picture of tropical ozone.
Inadequacy of Lu’s Data for Tropical Ozone Analysis:
– The data utilized by Lu (2022) are insufficient for a comprehensive evaluation of tropical stratospheric ozone, leading to inaccurate conclusions regarding ozone variations.
Absence of Tropical ‘Ozone Hole’ Threat:
– Evidence does not support the existence of a tropical ‘ozone hole’, and concerns raised by Lu (2022) regarding ozone depletion lack scientific merit.
Acknowledgments:
– Researchers acknowledging educational and research fellowships received during the study.
– Gratitude expressed for the facilitation of specific projects.
Review and Feedback:
– Recognition for comments and suggestions on the draft.
– Editorial support and review process described.
Impact and Insights:
– New insights on the impact of ozone-depleting substances on the Brewer-Dobson circulation.
– Significant radiative impact of volcanic aerosol in the lowermost stratosphere.
Climate Implications:
– Implications of potential future grand solar minimum for ozone layer and climate.
– Photochemical evolution of ozone in the lower tropical stratosphere.
Ozone Trends:
– Trends in stratospheric ozone sensitivity to recent large variability.
– Record-breaking increases in Arctic solar ultraviolet radiation caused by exceptionally large ozone depletion in 2020.
Research Studies:
– Stratospheric ozone trends for 1984–2021 in the SAGE II–OSIRIS–SAGE III/ISS composite dataset.
– Simulations of anthropogenic change in the strength of the Brewer–Dobson circulation.
Scientific Contributions:
– Quantifying the ozone and ultraviolet benefits already achieved by the Montreal Protocol.
– On the cause of recent variations in lower stratospheric ozone.
Historical Perspective:
– Changes in stratospheric ozone over time.
– Rapid increase in atmospheric iodine levels in the North Atlantic since the mid-20th century.
Homogenized (SWOOSH) Database:
– A long-term database for climate studies
– Published in 2016
Calibration of SBUV Ozone Data:
– Study by DeLand, Taylor, Huang, and Fisher
– Published in 2012
Sentinel-5P TROPOMI Total Ozone Column:
– Data set from Goddard Earth Sciences Data Center
– Accessible online since 2020
Large Losses of Total Ozone in Antarctica:
– Research by Farman, Gardiner, and Shanklin
– Revealed seasonal ClOx/NOx interaction in 1985
Global and Zonal Total Ozone Variations:
– Period: 1964–2000
– Study by Fioletov in 2002
Impact of Continuing CFC-11 Emissions on Stratospheric Ozone:
– Investigation by Fleming, Newman, Liang, and Daniel
– Published in 2020
Performance of the Ozone Mapping and Profiler Suite (OMPS) Products:
– Study by Flynn, Long, Wu, and others
– Evaluation conducted in 2014
Estimating Uncertainties in SBUV Version 8.6 Merged Profile Ozone Data Set:
– Research by Frith, Stolarski, Kramarova, and McPeters
– Published in 2017
Satellite and Model Climatologies Study:
– Comparison of stratospheric lifetime ratio of CFC-11 and CFC-12
– Analysis based on satellite data and model simulations
Halogens Influence on Climate:
– Efficiency of short-lived halogens in affecting climate
– Link between halogens and stratospheric ozone depletion
Ozone Profile Validation:
– Validation of 10-year SAO OMI ozone profile product
– Comparison with Aura MLS measurements
Assimilation Tests with TROPOMI Data:
– Monitoring and assimilation tests using TROPOMI data in the CAMS system
– Focus on near-real-time total column ozone monitoring
Iodine Chemistry in Climate Model:
– Study on iodine chemistry in the chemistry–climate model SOCOL-AERv2-I
– Implications of iodine chemistry on climate
Antarctic Ozone Hole Recovery:
– Investigation of signs indicating Antarctic ozone hole recovery
– Key findings related to ozone hole dynamics
Tropospheric Ozone Study:
– Exploration of factors controlling tropospheric ozone
– Insights into tropospheric ozone variations
Ozone Monitoring Instrument:
– Overview of the ozone monitoring instrument
– Role in monitoring atmospheric ozone levels
Frequency and Size of Ozone ‘Mini-Hole’ Events:
– McCormack and Hood reported on the frequency and size of ozone ‘mini-hole’ events at northern midlatitudes in February, showing the occurrence of these events in this region.
– This study was conducted in 1997 and provided valuable insights into the occurrence of ozone ‘mini-hole’ events.
Earth Probe Total Ozone Mapping Spectrometer (TOMS) Data:
– Müller et al.’s study in 1998 introduced the Earth probe Total Ozone Mapping Spectrometer (TOMS) data product user’s guide, providing valuable information on this ozone mapping technology.
– The guide can be accessed through the NASA website, offering a comprehensive resource for users.
Observations of Ozone-Poor Air in the Tropical Tropopause Layer:
– Newton et al.’s observations in 2018 highlighted the presence of ozone-poor air in the tropical tropopause layer, indicating significant findings in this area of study.
– The study’s publication in 2018 underscores the recent nature of these important observations.
Assessment of Ozone Performance:
– Smit et al.’s assessment of the performance of ECC-ozonesondes under quasi-flight conditions provided valuable insights into ozone sonde technology and its reliability.
– The study’s publication in 2007 indicates a fairly recent assessment of ozone monitoring technology.
Emergence of Healing in the Antarctic Ozone Layer:
– Solomon et al.’s study in 2016 discussed the emergence of healing in the Antarctic ozone layer, marking a significant positive development in the understanding of ozone recovery.
– The study’s recent publication date emphasizes the timeliness and relevance of this finding.
Long-Term Tropospheric Ozone Trends:
– Staehelin and Poberaj’s critical review in 2008 provided a comprehensive examination of long-term tropospheric ozone trends, offering a valuable resource for understanding historical variability.
– The publication’s focus on long-term trends highlights the importance of this research in assessing ozone changes over time.
Update on Ozone Profile Trends:
– Steinbrecht et al.’s update on ozone profile trends for the period 2000 to 2016 in 2017 provided recent and relevant information on ozone trends, making it a significant contribution to current knowledge.
– The study’s focus on a specific time period allows for a more detailed analysis of recent ozone profile trends.
Coherent Variations of Monthly Mean Total Ozone:
– Randel and Cobb’s study in 1994 discussed coherent variations of monthly mean total ozone and lower stratospheric temperature, providing valuable insights into the variability of ozone levels over time.
– The study’s early publication date underscores its foundational role in understanding ozone variations.
Identification of Ozone Recovery:
– Observational evidence does not support any current understanding for the identification of ozone recovery.
– Antarctic stratospheric nitrogen solar FTIR measurements of NOx vertical trends in polar ozone loss since 1989.
Stratospheric Ozone Trends:
– Seasonal stratospheric ozone trends over 2000–2018 have been derived from several merged data sets.
– Quantifying stratosphere-troposphere transport of ozone using balloon-borne ozonesondes, radar windprofilers and trajectory models.
Causes of Ozone Column Variability:
– Reassessment of causes of ozone column variability following the eruption of Mount Pinatubo using a nudged CCM.
Southern Hemisphere Additional Ozonesondes:
– Comparisons with satellites and ground-based instruments have been made related to the first reprocessing of Southern Hemisphere Additional Ozonesondes (SHADOZ) ozone profiles (1998–2016).
Tropical Ozone Trends:
– Regional and seasonal trends in tropical ozone from SHADOZ profiles have been referenced for models and satellite products.
World Meteorological Organization-Global Atmosphere Watch Program:
– TOST and WOUDC ozonesonde data have been made available for World Meteorological Organization-Global Atmosphere Watch Program (WMO-GAW), World Ozone and Ultraviolet Radiation Data Centre (WOUDC).
Extratropical Lower Stratospheric Ozone Decline:
– Recent decline in extratropical lower stratospheric ozone has been attributed to circulation changes.
Global Total Ozone Recovery Trends:
– Total ozone recovery trends from 1979 to 2016 have been attributed to ozone-depleting substance (ODS) changes derived from five merged ozone datasets.
–Raja Aditya
