Study of stratospheric composition using airborne submillimeter radiometry and a chemical transport model

The Airborne Submillimeter Radiometer (ASUR) was deployed aboard the Falcon research aircraft during the SCIAVALUE (SCIAMACHY - Scanning Imaging Absorption Spectrometer for Atmospheric ChartographY - Validation Utilization Experiment), the EUPLEX (European Polar and Lee wave Experiment), and the PAVE (Polar Aura Validation Experiment) campaigns. An impressive array of microwave measurements of O3, N2O, HCl, HNO3 and ClO is amassed during the missions from the tropics to the Arctic in various seasons.Using the data various satellite sensor measurements for different molecules are validated. In addition, a new model, the Bremen Chemical Transport Model (CTMB), is introduced. Evaluation of the Linearized ozone chemistry shows that the ozone profiles simulated with the Linoz model are accurate enough to be used for stratospheric chemistry and transport studies though the simulations show a low bias of about 9% in the middle stratosphere and a high bias of 10-30% in the lower and upper stratosphere, depending on altitude. The simulations for various years suggest that the N2O and NOy calculations depend greatly on the accuracy of the meteorological analyses used in the model. The simulations reveal that the N2O VMRs calculated with the parameterized chemistry are slightly smaller in the lower stratosphere. The inaccuracies in the wind analyses and in the model transport and uncertainties in the chemical reaction rates can be the reasons for the lower values. The N2O-NOy coupled chemistry is in good shape and the transport barriers are reasonably represented in the model. The comparison among the ASUR, the SLIMCAT and the CTMB profiles reveal the upper stratospheric ozone deficit in the SLIMCAT calculations. The comparisons also indicate that the transport process in the models is still to be improved

The unusual persistence of an ozone hole over a southern mid-latitude station during the Antarctic spring 2009: a multi-instrument study

International audienceRecord-low ozone column densities (with a minimum of 212 DU) persisted over three weeks at the Río Gallegos NDACC (Network for the Detection of Atmospheric Composition Change) station (51.5° S, 69.3° W) in November 2009. Total ozone remained two standard deviations below the climatological mean for five consecutive days during this period. The statistical analysis of 30 years of satellite data from the Multi Sensor Reanalysis (MSR) database for Río Gallegos revealed that such a long-lasting low-ozone episode is a rare occurrence. The event is examined using height-resolved ozone lidar measurements at Río Gallegos, and observations from satellite and ground-based instruments. The computed relative difference between the measured total ozone and the climatological monthly mean shows reductions varying between 10 and 30% with an average decrease of 25%. The mean absolute difference of total ozone column with respect to climatological monthly mean ozone column is around 75 DU. Extreme values of the UV index (UVI) were measured at the ground for this period, with the daily maximum UVI of around 13 on 15 and 28 November. The high-resolution MIMOSA-CHIM (Modélisation Isentrope du transport Méso-échelle de l'Ozone Stratosphérique par Advection) model was used to interpret the ozone depletion event. An ozone decrease of about 2 ppmv was observed in mid-November at the 550 K isentropic level (~22 km). The position of Río Gallegos relative to the polar vortex was classified using equivalent latitude maps. During the second week of November, the vortex was over the station at all isentropic levels, but after 20 November and until the end of the month, only the 10 lower levels in the stratosphere were affected by vortex overpasses with ozone poor air masses. A rapid recovery of the ozone column density was observed later, due to an ozone rich filament moving over Río Gallegos between 18 and 24 km in the first two weeks of December 2009

Physics and chemistry of stratospheric ozone and interactions with climate change

Ozone is one of the key constituents in the atmosphere, although present only in trace amounts. The stratospheric ozone plays a pivotal role in regulating the incidence of harmful ultra-violet radiation (400- 100 nm) and radiative balance of the earth, and thus influences the global climate. This thesis deals with the spatial, temporal and vertical evolution of polar stratospheric ozone and its interactions with climate change over 1979-2012, with an emphasis on the winters of 2000s. Analysis of the dynamical situation in the Arctic winters reveals that there is an increase in the occurrence of major warmings (MWs) in recent years (1998/1999-2009/2010), as there were 13MWs in the 12 winters (⇠11 MWs/decade), although the long-term average (1957/1958-2009/2010) of the frequency stays around its historical value (⇠7MWs/decade). A study of the chemical ozone loss in the past 17 winters (1993/1994-2009/2010) suggests that the loss is inversely proportional to the intensity and timing of MWs in each winter, where early (December-January) MWs lead to limited loss. This high frequency of the MWs has significant implications for stratospheric ozone trends and hence, the Arctic and global climate. A detailed assessment of the Arctic winters 1996/1997 and 2002/2003-2010/2011 shows that the winter 2002/2003 had a MW and three minor warmings. However, the winter still had a cumulative ozone loss of ⇠1.5ppmv at 450-500K or 65DU over 400-550K by the end of March, apart from the record loss of ⇠0.7ppmv in December-January, as no other winter had such a large loss during the early winter over 1988/1989-2010/2011. In contrast, the largest ozone loss ever observed was in 2010/2011, about 2.5 ppmv at 400-550K or 140DU over 350-550K. Our study shows that the loss in 2010/2011 was close to that found in some Antarctic winters, for the first time in the observed history. The prolonged strong chlorine activation and denitrification during the winter triggered this record loss. The loss in other winters was between 0.7 and 1.6 ppmv at around 475 K or 40 and 115 DU over 350-550 K, in which the smallest loss was estimated in the warm winter 2005/2006. In order to make a long-term ozone loss time series for Antarctica, a method is introduced and applied to ground-based and space-borne total column ozone observations for the 1989-2012 period. The vortex- averaged ozone loss in the Antarctic is shown to be about 33-50% during 1989-1992 in agreement with the increase in halogens during that period, and then stayed at around 48% due to saturation of the loss. The loss in warmer winters (e.g. 2002 and 2004) is slightly smaller (37-46%) and the loss in very cold winters (e.g. 2003 and 2006) is relatively larger (52-55%). The maximum loss in the Antarctic is observed from mid-September to mid-October, and the peak loss rate is found in the August-early September period, with an average of about 0.5%/day. Furthermore, analysis with high resolution ozone profile measurements and simulations for the Antarctic winters 2004-2010 also showed the largest ozone loss in the colder winters of 2005 and 2006 with about 3.5 ppmv at 450-550 K or around 170 DU over 350-850 K, and the smallest loss in the warmer winters of 2004 and 2010 with about 2.5 ppmv at 450-550 K or around 140 DU over 350-850 K. The peak ozone loss altitude in Antarctica is around 500 K. However, the very cold winters show a higher and warmer winters show a lower shift in the peak loss altitudes (about 25 K), exhibiting a clear distinction between various winters in terms of the altitude of maximum loss. The study further indicates that the comparatively smaller Antarctic ozone loss and ozone holes in the recent winters (2004-2010) were due to the effect of a number of minor warmings during the period.L'ozone est un constituant important dans la chimie de l'atmosphère, cela malgré sa faible concentration. L'ozone stratoshérique joue un rôle essentiel à la fois dans la régulation des radiations ultraviolettes du soleil connues pour être dangereuses aux différentes formes de vie sur Terre et également dans l'équilibre radiatif influençant le climat global. Cette thèse est consacrée à l'étude de l'évolution temporelle et spatiale de l'ozone stratosphérique polaire entre 1979 et 2012, ainsi qu'à son interaction avec le changement climatique, avec une attention particulière pour les années après 2000. L'analyse de la dynamique des hivers arctiques révèle une augmentation des évènements de forts réchauffements (EFR) ces dernières années (comparaisons faites entre les hivers 1998/99 et 2009/10). Alors qu'on compte 13 EFRs lors des 12 derniers hivers (soit 11EFR/décennie), le nombre moyen entre les hivers 1957/58 et 2009/10 s'élève à 7 EFR/décennie. Une étude chimique de la destruction de l'ozone lors des 17 derniers hivers (1993/94-2009/10) montre que celle-ci est inversement proportionnelle à l'intensité des EFRs. De même, il semble que, pour chaque hiver, plus l'EFR se produit tôt dans l'année (Décembre-Janvier), plus la perte d'ozone enregistrée est faible. Ainsi la fréquence des EFRs lors des récents hivers arctiques joue un rôle significatif sur la concentration moyenne d'ozone stratospherique dans l'hémisphère Nord et par conséquent également sur le climat arctique et global. Une analyse détaillée de la destruction d'ozone lors des hivers arctiques 1996/97 et 2002/03-2010/11 montre que l'hiver 2002/03 a subit un EFR et trois réchauffements mineurs. Pourtant, lors de cet hiver, une grande quantité d'ozone a été détruite à la fin du mois de mars. Environ 1.5 ppmv détruit entre 450 et 500 K, ou 65 DU entre 400 et 550 K qui s'ajoutent aux 0.7 ppmv détruit au mois de décembre (il s'agit de la plus forte perte d'ozone enregistrée au mois de décembre entre les hivers 1988/89 et 2010/11). La plus forte perte d'ozone enregistrée sur un hiver entier lors de cette décennie a été observée en 2010/11 (soit environ 2.5ppmv entre 400-500K ou 140DU entre 350-550K). L'étude montre également que, pour la première fois depuis que nous observons l'ozone, la quantité d'ozone détruite lors de cet hiver est comparable à celle détruite lors de certains hivers en Antarctique. Nous montrons que cette destruction d'ozone record est due à une activation des chlorines et une denitrification importante et prolongée lors de cet hiver. La perte d'ozone lors des autres hivers est de l'ordre de 0.7 à 1.6 ppmv autour de 475 K ou 40 à 115 DU entre 350 et 550 K (la plus petite destruction d'ozone ayant été mesurée lors de l'hiver 2005/06, particulièrement chaud). Pour l'Antarctique, une méthode est proposée pour estimer la tendance à long terme de la destruction chimique de l'ozone. Cette méthode est utilisée sur la période 1989-2012 pour estimer, en colonne totale, les tendances d'ozone à partir d'observations au sol et satellitaires. A l'intérieur du vortex polaire, nous montrons que la perte moyenne d'ozone se situe entre 33-50% pendant la période 1989-1992. Cette valeur est en accord avec l'augmentation de la concentration d'halogène lors de cette même période. Après cette période, la perte moyenne d'ozone semble atteindre une valeur de saturation aux alentours de 48%. La destruction d'ozone lors des hivers les plus chauds (e.g. 2002 et 2004) est légèrement inférieure (37-46%) et celle des hivers les plus froids (e.g. 2003 et 2006), légèrement supérieure (52-55%). La perte maximum d'ozone en Antarctique est observée entre le milieu du mois de septembre et le milieu du mois d'octobre, et la plus forte valeur de perte d'ozone est observée entre fin août et début septembre, atteignant en moyenne 0.5%/jr. Des analyses basées à la fois sur des profils d'ozone simulés grâce à un modèle haute résolution et sur des profils observés par instrument satellitaire lors des 7 hivers antarctiques entre 2004 et 2010, montrent également que les plus fortes pertes d'ozone coincident avec les hivers les plus froids de 2005 et 2006. Lors de ces deux hivers, la perte d'ozone a atteint 3.5 ppmv entre 450 et 550 K, ou 180 DU entre 350 et 850 K. Les deux hivers les plus chauds (2004 et 2010) ont connu les plus faibles pertes d'ozone (environ 2.5 ppmv entre 450 et 550 K, ou 160 DU entre 350 et 850 K). En Antarctique, l'altitude du maximum de destruction d'ozone est 500 K, cependant, pendant les hivers les plus froids et les hivers les plus chauds, ce maximum est 25 K plus haut (respectivement plus bas). Ce déplacement du maximum de perte permettant ainsi clairement de distinguer les hivers froids des hivers chauds. Cette étude montre également que la relative faible perte d'ozone ainsi que le trou d'ozone des récents hivers antarctiques (2004-2010) sont due à des phénomènes de réchauffement moindre

Studien über die Zusammensetzung der Stratosphäre unter Verwendung der

The Airborne Submillimeter Radiometer (ASUR) was deployed aboard the Falcon research aircraft during the SCIAVALUE (SCIAMACHY - Scanning Imaging Absorption Spectrometer for Atmospheric ChartographY - Validation Utilization Experiment), the EUPLEX (European Polar and Lee wave Experiment), and the PAVE (Polar Aura Validation Experiment) campaigns. An impressive array of microwave measurements of O3, N2O, HCl, HNO3 and ClO is amassed during the missions from the tropics to the Arctic in various seasons.Using the data various satellite sensor measurements for different molecules are validated. In addition, a new model, the Bremen Chemical Transport Model (CTMB), is introduced. Evaluation of the Linearized ozone chemistry shows that the ozone profiles simulated with the Linoz model are accurate enough to be used for stratospheric chemistry and transport studies though the simulations show a low bias of about 9% in the middle stratosphere and a high bias of 10-30% in the lower and upper stratosphere, depending on altitude. The simulations for various years suggest that the N2O and NOy calculations depend greatly on the accuracy of the meteorological analyses used in the model. The simulations reveal that the N2O VMRs calculated with the parameterized chemistry are slightly smaller in the lower stratosphere. The inaccuracies in the wind analyses and in the model transport and uncertainties in the chemical reaction rates can be the reasons for the lower values. The N2O-NOy coupled chemistry is in good shape and the transport barriers are reasonably represented in the model. The comparison among the ASUR, the SLIMCAT and the CTMB profiles reveal the upper stratospheric ozone deficit in the SLIMCAT calculations. The comparisons also indicate that the transport process in the models is still to be improved

Physics and chemistry of stratospheric ozone and interactions with climate change

Ozone is one of the key constituents in the atmosphere, although present only in trace amounts. The stratospheric ozone plays a pivotal role in regulating the incidence of harmful ultra-violet radiation (400- 100 nm) and radiative balance of the earth, and thus influences the global climate. This thesis deals with the spatial, temporal and vertical evolution of polar stratospheric ozone and its interactions with climate change over 1979-2012, with an emphasis on the winters of 2000s. Analysis of the dynamical situation in the Arctic winters reveals that there is an increase in the occurrence of major warmings (MWs) in recent years (1998/1999-2009/2010), as there were 13MWs in the 12 winters (⇠11 MWs/decade), although the long-term average (1957/1958-2009/2010) of the frequency stays around its historical value (⇠7MWs/decade). A study of the chemical ozone loss in the past 17 winters (1993/1994-2009/2010) suggests that the loss is inversely proportional to the intensity and timing of MWs in each winter, where early (December-January) MWs lead to limited loss. This high frequency of the MWs has significant implications for stratospheric ozone trends and hence, the Arctic and global climate. A detailed assessment of the Arctic winters 1996/1997 and 2002/2003-2010/2011 shows that the winter 2002/2003 had a MW and three minor warmings. However, the winter still had a cumulative ozone loss of ⇠1.5ppmv at 450-500K or 65DU over 400-550K by the end of March, apart from the record loss of ⇠0.7ppmv in December-January, as no other winter had such a large loss during the early winter over 1988/1989-2010/2011. In contrast, the largest ozone loss ever observed was in 2010/2011, about 2.5 ppmv at 400-550K or 140DU over 350-550K. Our study shows that the loss in 2010/2011 was close to that found in some Antarctic winters, for the first time in the observed history. The prolonged strong chlorine activation and denitrification during the winter triggered this record loss. The loss in other winters was between 0.7 and 1.6 ppmv at around 475 K or 40 and 115 DU over 350-550 K, in which the smallest loss was estimated in the warm winter 2005/2006. In order to make a long-term ozone loss time series for Antarctica, a method is introduced and applied to ground-based and space-borne total column ozone observations for the 1989-2012 period. The vortex- averaged ozone loss in the Antarctic is shown to be about 33-50% during 1989-1992 in agreement with the increase in halogens during that period, and then stayed at around 48% due to saturation of the loss. The loss in warmer winters (e.g. 2002 and 2004) is slightly smaller (37-46%) and the loss in very cold winters (e.g. 2003 and 2006) is relatively larger (52-55%). The maximum loss in the Antarctic is observed from mid-September to mid-October, and the peak loss rate is found in the August-early September period, with an average of about 0.5%/day. Furthermore, analysis with high resolution ozone profile measurements and simulations for the Antarctic winters 2004-2010 also showed the largest ozone loss in the colder winters of 2005 and 2006 with about 3.5 ppmv at 450-550 K or around 170 DU over 350-850 K, and the smallest loss in the warmer winters of 2004 and 2010 with about 2.5 ppmv at 450-550 K or around 140 DU over 350-850 K. The peak ozone loss altitude in Antarctica is around 500 K. However, the very cold winters show a higher and warmer winters show a lower shift in the peak loss altitudes (about 25 K), exhibiting a clear distinction between various winters in terms of the altitude of maximum loss. The study further indicates that the comparatively smaller Antarctic ozone loss and ozone holes in the recent winters (2004-2010) were due to the effect of a number of minor warmings during the period.L'ozone est un constituant important dans la chimie de l'atmosphère, cela malgré sa faible concentration. L'ozone stratoshérique joue un rôle essentiel à la fois dans la régulation des radiations ultraviolettes du soleil connues pour être dangereuses aux différentes formes de vie sur Terre et également dans l'équilibre radiatif influençant le climat global. Cette thèse est consacrée à l'étude de l'évolution temporelle et spatiale de l'ozone stratosphérique polaire entre 1979 et 2012, ainsi qu'à son interaction avec le changement climatique, avec une attention particulière pour les années après 2000. L'analyse de la dynamique des hivers arctiques révèle une augmentation des évènements de forts réchauffements (EFR) ces dernières années (comparaisons faites entre les hivers 1998/99 et 2009/10). Alors qu'on compte 13 EFRs lors des 12 derniers hivers (soit 11EFR/décennie), le nombre moyen entre les hivers 1957/58 et 2009/10 s'élève à 7 EFR/décennie. Une étude chimique de la destruction de l'ozone lors des 17 derniers hivers (1993/94-2009/10) montre que celle-ci est inversement proportionnelle à l'intensité des EFRs. De même, il semble que, pour chaque hiver, plus l'EFR se produit tôt dans l'année (Décembre-Janvier), plus la perte d'ozone enregistrée est faible. Ainsi la fréquence des EFRs lors des récents hivers arctiques joue un rôle significatif sur la concentration moyenne d'ozone stratospherique dans l'hémisphère Nord et par conséquent également sur le climat arctique et global. Une analyse détaillée de la destruction d'ozone lors des hivers arctiques 1996/97 et 2002/03-2010/11 montre que l'hiver 2002/03 a subit un EFR et trois réchauffements mineurs. Pourtant, lors de cet hiver, une grande quantité d'ozone a été détruite à la fin du mois de mars. Environ 1.5 ppmv détruit entre 450 et 500 K, ou 65 DU entre 400 et 550 K qui s'ajoutent aux 0.7 ppmv détruit au mois de décembre (il s'agit de la plus forte perte d'ozone enregistrée au mois de décembre entre les hivers 1988/89 et 2010/11). La plus forte perte d'ozone enregistrée sur un hiver entier lors de cette décennie a été observée en 2010/11 (soit environ 2.5ppmv entre 400-500K ou 140DU entre 350-550K). L'étude montre également que, pour la première fois depuis que nous observons l'ozone, la quantité d'ozone détruite lors de cet hiver est comparable à celle détruite lors de certains hivers en Antarctique. Nous montrons que cette destruction d'ozone record est due à une activation des chlorines et une denitrification importante et prolongée lors de cet hiver. La perte d'ozone lors des autres hivers est de l'ordre de 0.7 à 1.6 ppmv autour de 475 K ou 40 à 115 DU entre 350 et 550 K (la plus petite destruction d'ozone ayant été mesurée lors de l'hiver 2005/06, particulièrement chaud). Pour l'Antarctique, une méthode est proposée pour estimer la tendance à long terme de la destruction chimique de l'ozone. Cette méthode est utilisée sur la période 1989-2012 pour estimer, en colonne totale, les tendances d'ozone à partir d'observations au sol et satellitaires. A l'intérieur du vortex polaire, nous montrons que la perte moyenne d'ozone se situe entre 33-50% pendant la période 1989-1992. Cette valeur est en accord avec l'augmentation de la concentration d'halogène lors de cette même période. Après cette période, la perte moyenne d'ozone semble atteindre une valeur de saturation aux alentours de 48%. La destruction d'ozone lors des hivers les plus chauds (e.g. 2002 et 2004) est légèrement inférieure (37-46%) et celle des hivers les plus froids (e.g. 2003 et 2006), légèrement supérieure (52-55%). La perte maximum d'ozone en Antarctique est observée entre le milieu du mois de septembre et le milieu du mois d'octobre, et la plus forte valeur de perte d'ozone est observée entre fin août et début septembre, atteignant en moyenne 0.5%/jr. Des analyses basées à la fois sur des profils d'ozone simulés grâce à un modèle haute résolution et sur des profils observés par instrument satellitaire lors des 7 hivers antarctiques entre 2004 et 2010, montrent également que les plus fortes pertes d'ozone coincident avec les hivers les plus froids de 2005 et 2006. Lors de ces deux hivers, la perte d'ozone a atteint 3.5 ppmv entre 450 et 550 K, ou 180 DU entre 350 et 850 K. Les deux hivers les plus chauds (2004 et 2010) ont connu les plus faibles pertes d'ozone (environ 2.5 ppmv entre 450 et 550 K, ou 160 DU entre 350 et 850 K). En Antarctique, l'altitude du maximum de destruction d'ozone est 500 K, cependant, pendant les hivers les plus froids et les hivers les plus chauds, ce maximum est 25 K plus haut (respectivement plus bas). Ce déplacement du maximum de perte permettant ainsi clairement de distinguer les hivers froids des hivers chauds. Cette étude montre également que la relative faible perte d'ozone ainsi que le trou d'ozone des récents hivers antarctiques (2004-2010) sont due à des phénomènes de réchauffement moindre

The signs of Antarctic ozone hole recovery

International audienceAbsorption of solar radiation by stratospheric ozone affects atmospheric dynamics and chemistry, and sustains life on Earth by preventing harmful radiation from reaching the surface. Significant ozone losses due to increases in the abundances of ozone depleting substances (ODSs) were first observed in Antarctica in the 1980s. Losses deepened in following years but became nearly flat by around 2000, reflecting changes in global ODS emissions. Here we show robust evidence that Antarctic ozone has started to recover in both spring and summer, with a recovery signal identified in springtime ozone profile and total column measurements at 99% confidence for the first time. Continuing recovery is expected to impact the future climate of that region. Our results demonstrate that the Montreal Protocol has indeed begun to save the Antarctic ozone layer

Signatures of the Antarctic ozone loss saturation in the late 1980s

The chemical ozone loss in the Antarctic due to increased halogen loading was first noticed in the late 1970s and early 1980s. Intense monitoring of the processes by various measurement clusters has been initiated since then, including ozone soundings at a number of Antarctic stations in each winter and spring. We examine the ozone measurements taken by the sondes from a group of stations in the continent to analyse the progress, saturation and anticipated decrease of the ozone depletion in the Antarctic. The analysis of the data reveals that, in agreement with available records, the ozone loss in the region intensified by the mid 1980s. The saturation of ozone loss has, however, shown to be started by 1987 in contrast to previously published results. The signatures of saturation are clearly evident at a range of lower stratospheric isentropic levels between 350 and 500 K in October. In September, the saturation is observed from 1991 onwards. The diagnosis is performed on a potential temperature equivalent latitude (EqL) surface to distinguish the dependency of loss saturation on EqL. The study shows that the saturation has taken place irrespective of EqL over the years in the range of 65-90 EqL covered by the ozone soundings; i.e. above the 65 degree EqL cut off used in this study. While the saturation of ozone depletion continues until now, the average ozone values inside the vortex show a clear levelling off after 1996. The regression of vortex averaged ozone against Equivalent Effective Stratospheric Chlorine for the 1997-2010 period corroborates the levelling off of ozone depletion. It also suggests that the complete recovery of ozone layer in the Antarctic is still a few decades away

Numerical simulation of ozone loss in the Antarctic winters 2005-2008: Comparison with MLS measurements

International audienceThe ozone loss in the recent Antarctic winters were high enough to pause a lag in the recovery phase of stratospheric ozone above this continent. We quantitatively examine the extent of ozone loss variability during 2005-2008 with simulations from a high resolution chemical transport model, MIMOSA-CHIM. The simulated results are cross-checked with the observed loss from Microwave Limb Sounder (MLS) satellite sensor data. This study uses the vortex averaged data at the potential temperature level 475 K from both MIMOSA and MLS to estimate the ozone loss by transport method. Minimum temperatures calculated from ECMWF analyzes over 50-90°S at 475 K are coldest in 2008 during June-July and in 2006 during September-November. In general, Antarctic winters experience NAT temperatures from mid-May to mid-October and ICE temperatures from June to September. Due to the saturation of chemical ozone loss, the year-to-year difference in temperatures do not have a large effect. The estimated cumulative ozone loss from MIMOSA-CHIM at 475 K is 3.2 in 2005, 2.9 in 2006, 2.8 in 2007 and 2.0 ppm in 2008. The measured cumulative loss in the respective years also show similar values: respectively 3.3, 3.2, 2.8 and 2.2 ppm in 2005, 2006, 2007 and 2008. Both data sets show the same loss trend, as the cumulative loss is highest in 2005 followed by 2006 and the lowest in 2008, and are in accord with the chlorine activation and denitrification found in the respective winters. The simulations in 2008 lack adequate diabatic descent as assessed from tracer simulations in comparison with measurements. This eventually produced relatively lower values for ozone loss in 2008 in both data sets even though the observed chlorine activation was found to be similar to previous winters

Wintertime direct radiative effects due to black carbon (BC) over the Indo-Gangetic Plain as modelled with new BC emission inventories in CHIMERE

International audienceTo reduce the uncertainty in climatic impacts induced by black carbon (BC) from global and regional aerosol–climate model simulations, it is a foremost requirement to improve the prediction of modelled BC distribution, specifically over the regions where the atmosphere is loaded with a large amount of BC, e.g. the Indo-Gangetic Plain (IGP) in the Indian subcontinent. Here we examine the wintertime direct radiative perturbation due to BC with an efficiently modelled BC distribution over the IGP in a high-resolution (0.1∘ × 0.1∘) chemical transport model, CHIMERE, implementing new BC emission inventories. The model efficiency in simulating the observed BC distribution was assessed by executing five simulations: Constrained and bottomup (bottomup includes Smog, Cmip, Edgar, and Pku). These simulations respectively implement the recently estimated India-based observationally constrained BC emissions (Constrainedemiss) and the latest bottom-up BC emissions (India-based: Smog-India; global: Coupled Model Intercomparison Project phase 6 – CMIP6, Emission Database for Global Atmospheric Research-V4 – EDGAR-V4, and Peking University BC Inventory – PKU). The mean BC emission flux from the five BC emission inventory databases was found to be considerably high (450–1000 kg km−2 yr−1) over most of the IGP, with this being the highest (> 2500 kg km−2 yr−1) over megacities (Kolkata and Delhi). A low estimated value of the normalised mean bias (NMB) and root mean square error (RMSE) from the Constrained estimated BC concentration (NMB: < 17 %) and aerosol optical depth due to BC (BC-AOD) (NMB: 11 %) indicated that simulations with Constrainedemiss BC emissions in CHIMERE could simulate the distribution of BC pollution over the IGP more efficiently than with bottom-up emissions. The high BC pollution covering the IGP region comprised a wintertime all-day (daytime) mean BC concentration and BC-AOD respectively in the range 14–25 µg m−3 (6–8 µg m−3) and 0.04–0.08 from the Constrained simulation. The simulated BC concentration and BC-AOD were inferred to be primarily sensitive to the change in BC emission strength over most of the IGP (including the megacity of Kolkata), but also to the transport of BC aerosols over megacity Delhi. Five main hotspot locations were identified in and around Delhi (northern IGP), Prayagraj–Allahabad–Varanasi (central IGP), Patna–Palamu (mideastern IGP), and Kolkata (eastern IGP). The wintertime direct radiative perturbation due to BC aerosols from the Constrained simulation estimated the atmospheric radiative warming (+30 to +50 W m−2) to be about 50 %–70 % larger than the surface cooling. A widespread enhancement in atmospheric radiative warming due to BC by 2–3 times and a reduction in surface cooling by 10 %–20 %, with net warming at the top of the atmosphere (TOA) of 10–15 W m−2, were noticed compared to the atmosphere without BC, for which a net cooling at the TOA was exhibited. These perturbations were the strongest around megacities (Kolkata and Delhi), extended to the eastern coast, and were inferred to be 30 %–50% lower from the bottomup than the Constrained simulation