We report on a detailed time series analysis of long total column ozone (TO) records based on mul... more We report on a detailed time series analysis of long total column ozone (TO) records based on multi-satellite observations of daily resolution. We concentrate on three geographic latitudes over and around the Antarctic area, specifically on three circles at 58.5 ∘ S, 59.5 ∘ S, and 79.5 ∘ S. Almost continuous observations are available at the two former latitudes; however, data are lacking during the polar winter periods at 79.5 ∘ S, because the measurement technique requires sunlight. The methodology is motivated by level-crossing statistics, where subsets of the records above or below particular threshold levels are evaluated. Long-term trend reversal at around the turn of the century is already detectable for low TO levels in the raw time series in the "ozone-hole" region (79.5 ∘ S). In order to overcome the apparent non-stationarities of the time series, we determined daily TO differences (ΔTO) belonging to the same geographic longitudes between the different latitudinal circles. The result is a stable, stationary behavior for small (absolute) ΔTO values in the period January-February-March without any significant detectable trends. The high absolute value ΔTO subsets (September-October-November) indicate a robust trend reversal in the middle of the 1990s. The observed trend reversal in the total column ozone time series is consistent with the temporal development of the stratospheric halogen loading. However, a close correspondence of ozone and halogen turnaround years is not expected because of the statistical uncertainties in the determination of the ozone turnaround, and the many factors contributing to ozone depletion processes.
Dissociation induced by cosmic rays of chlorofluorocarbons (CFC) and HCl on the surfaces of polar... more Dissociation induced by cosmic rays of chlorofluorocarbons (CFC) and HCl on the surfaces of polar stratospheric clouds (PSC) has been suggested as playing a significant role in causing the ozone hole. However, observed stratospheric CFC distributions are inconsistent with a destruction of CFC on PSC surfaces and no significant correlation exists between ozone levels and cosmic-ray activity inside the polar regions. Model simulations indicate that this mechanism can have only a limited impact on chemical ozone loss and thus on the recovery of stratospheric ozone.
Ozone is one of the most important trace species in the atmosphere. Therefore, the history of res... more Ozone is one of the most important trace species in the atmosphere. Therefore, the history of research on ozone has also received a good deal of attention. Here a short overview of ozone research (with a focus on the stratosphere) is given, starting from the first atmospheric measurements and ending with current developments. It is valuable to study the history of ozone research, because much can be learned for current research from an understanding of how previous discoveries were made. Moreover, since the 1970s, the history of ozone research has also encompassed also the history of the human impact on the ozone layer and thus the history of policy measures taken to protect the ozone layer, notably the Montreal Protocol and its amendments and adjustments. The history of this development is particularly important because it may serve as a prototype for the development of policy measures for the protection of the Earth's climate. Zusammenfassung Ozon ist einer der wichtigsten Spurenstoffe in der Atmosphäre. Daher wurde auch der Geschichte der Ozonforschung viel Aufmerksamkeit gewidmet. Hier wird ein kurzerÜberblicküber die Ozonforschung gegeben (mit dem Fokus auf der Stratosphäre); beginnend mit den ersten atmosphärischen Ozonmessungen und endend mit aktuellen Entwicklungen. Das Studium der Geschichte der Ozonforschung ist hilfreich, da man für die aktuelle Forschung viel lernen kann, wenn man versteht, wie frühere Entdeckungen gemacht wurden. Seit den siebziger Jahren des vergangenen Jahrhunderts umfasst die Geschichte der Ozonforschung darüberhinaus die Geschichte des Einflusses des Menschen auf die Ozonschicht und damit auch die Geschichte der politischen Maßnahmen, die getroffen wurden, um die Ozonschicht zu schützen; vor allem das Montreal Protokoll sowie seine Anpassungen und Ergänzungen. Die Geschichte dieser Entwicklungen ist insbesonders von Bedeutung, da sie als Modell für die Entwicklung von politischen Maßnahmen zum Schutz des Klimas der Erde dienen kann.
The edge of the Arctic vortex constitutes a strong barrier to transport; however, the extent of i... more The edge of the Arctic vortex constitutes a strong barrier to transport; however, the extent of isolation of the vortex air as a function of altitude and season is relatively poorly quantified. In this study, by examining the transport of midlatitude air parcels across the vortex edge into the vortex, we analyze the permeability of the vortex edge. With the three-dimensional version of CLaMS (Chemical Lagrangian Model of the Stratosphere) we explore the dilution of the vortex air due to mixing in winter 1999-2000. An artificial, passive tracer was initialized on 1 December 1999 inside the polar vortex with a value of 100% and with a value of zero outside the polar vortex. Using several different definitions of the vortex edge, the resulting intrusions of midlatitude air into the vortex show the same mean features. This demonstrates that the diagnosed dilution does not strongly depend on the details of the definition of the vortex edge. At about the end of March 2000, the vertical structure of the vortex consisted of well-isolated, pure vortex layers around 500 K and 750 K, with some more diluted layers in between and at the vortex bottom. The influence of wave activity on the evolution of the intrusion layers is studied. The divergence of the Eliassen-Palm flux shows such a high variability during the whole period that it is not possible to assess a direct causality of certain intrusion layers and some specific patterns. Some characteristics of the vortex edge, in particular the shape of the gradient of potential vorticity (PV), can influence the dilution of the vortex. In cases without a distinct maximum in the PV gradient, the defined ''vortex edge'' may vary substantially from day to day. The comparison of some properties of the vortex (wind speed, PV field, area of the vortex, the maximum of the PV gradient) of undisturbed versus diluted layers and the variation in time of the intrusions were analyzed. All observed intrusions begin in conditions of weak PV gradient, indicating that the value of the maximum of the PV gradient may be used as a quantitative measure of the permeability of the vortex edge.
A recent paper [J. Chem. Phys.128, 041102 (2008)] reports resonant dissociative electron transfer... more A recent paper [J. Chem. Phys.128, 041102 (2008)] reports resonant dissociative electron transfer (RDET) to CCl4 in liquid ethanol. Part of the motivation for this work was the proposed importance of RDET processes for stratospheric ozone chemistry via dissociative electron attachment (DEA) triggered by cosmic ray activity in the polar winter stratosphere. In the present comment, it is argued that the relevance of DEA-induced destruction of chlorofluorocarbons (CFCs) in the polar stratosphere as a possible pathway for rapid chemical ozone destruction should not be a motivation for studies of DEA on CFC molecules; no correlation is observed between polar chemical ozone loss and cosmic ray activity. In any event, the relevance of this process as a key mechanism for the formation of the ozone hole should be presented as an issue debated in the scientific literature rather than as an established scientific fact.
Uncertainties in reactive uptake coefficients for pm 2 cm-a. For reaction R1 on NAT, the two sche... more Uncertainties in reactive uptake coefficients for pm 2 cm-a. For reaction R1 on NAT, the two schemes are in reactions involving HCI, CIONO2 and HOCI on nitric acid reasonable agreement at the ice frost point (2 hrs < r <7 trihydrate (N• and sulfuric acid tetrahydrate (SAT) are hrs), but differ substantially just below the NAT formation shown to affect modeled Arctic stratospheric ozone depletion temperature (1 day < r < 3 months). It is therefore under in a photochemical box model. The main contribution to the difference arises from the reaction ClONO• + HCl • Cl• + HNOa in early to midwinter. During this period, differences in predicted HCl and ClONO9• are more than 1 ppbv for several weeks when an upper limit for solid PSC existence is assumed. Ozone depletion is greater when liquid aerosols persist through the winter compared with cases where solid particles are assumed to form.
Satellite observations show that the enormous solar proton events (SPEs) in October-November 2003... more Satellite observations show that the enormous solar proton events (SPEs) in October-November 2003 had significant effects on the composition of the stratosphere and mesosphere in the polar regions. After the October-November 2003 SPEs and in early 2004, significant enhancements of NO x (=NO+NO 2) in the upper stratosphere and lower mesosphere in the Northern Hemisphere were observed by several satellite instruments. Here we present global full chemistry calculations performed with the CLaMS model to study the impact of mesospheric NO x intrusions on Arctic polar ozone loss processes in the stratosphere. Several model simulations are preformed with different upper boundary conditions for NO x at 2000 K potential temperature (≈50 km altitude). In our study we focus on the impact of the non-local production of NO x , which means the downward transport of enhanced NO x from the mesosphere to the stratosphere. The local production of NO x in the stratosphere is neglected. Our findings show that intrusions of mesospheric air into the stratosphere, transporting high burdens of NO x , affect the composition of the Arctic polar region down to about 400 K (≈17-18 km). We compare our simulated NO x and O 3 mixing ratios with satellite observations by ACE-FTS and MIPAS processed at IMK/IAA and derive an upper limit for the ozone loss caused by enhanced mesospheric NO x. Our findings show that in the Arctic polar vortex (equivalent lat.>70 • N) the accumulated column ozone loss between 350-2000 K potential temperature (≈14-50 km altitude) caused by the SPEs in October-November 2003 in the stratosphere is up to 3.3 DU with an upper limit of 5.5 DU until end of November. Further, we
1-year data sets of monthly averaged nitrous oxide (N 2 O) and ozone (O 3) derived from satellite... more 1-year data sets of monthly averaged nitrous oxide (N 2 O) and ozone (O 3) derived from satellite measurements were used as a tool for the evaluation of atmospheric photochemical models. Two 1-year data sets, one solar occultation data set derived from the Improved Limb Atmospheric Spectrometer (ILAS and ILAS-II) and one limb sounding data set derived from the Odin Sub-Millimetre Radiometer (Odin/SMR) were employed. Here, these data sets are used for the evaluation of two Chemical Transport Models (CTMs), the Karlsruhe Simulation Model of the Middle Atmosphere (KASIMA) and the Chemical Lagrangian Model of the Stratosphere (CLaMS) as well as for one Chemistry-Climate Model (CCM), the atmospheric chemistry general circulation model ECHAM5/MESSy1 (E5M1) in the lower stratosphere with focus on the Northern Hemisphere. Since the Odin/SMR measurements cover the entire hemisphere, the evaluation is performed for the entire hemisphere as well as for the low latitudes, midlatitudes and high latitudes using the Odin/SMR 1-year data set as reference. To assess the impact of using different data sets for such an evaluation study we repeat the evaluation for the polar lower stratosphere using the ILAS/ILAS-II data set. Only small differences were found using ILAS/ILAS-II instead of Odin/SMR as a reference, thus, showing that the results are not influenced by the particular satellite data set used for the evaluation. The evalu
Low stratospheric temperatures are known to be responsible for heterogeneous chlorine activation ... more Low stratospheric temperatures are known to be responsible for heterogeneous chlorine activation that leads to polar ozone depletion. Here, we discuss the temperature threshold below which substantial chlorine activation occurs. We suggest that the onset of chlorine activation is dominated by reactions on cold binary aerosol particles, without the formation of polar stratospheric clouds (PSCs), i.e. without any significant uptake of HNO 3 from the gas phase. Using reaction rates on cold binary aerosol in a model of stratospheric chemistry, a chlorine activation threshold temperature, T ACL , is derived. At typical stratospheric conditions, T ACL is similar in value to T NAT (within 1-2 K), the highest temperature at which nitric acid trihydrate (NAT) can exist. T NAT is still in use to parameterise the threshold temperature for the onset of chlorine activation. However, perturbations can cause T ACL to differ from T NAT : T ACL is dependent upon H 2 O and potential temperature, but unlike T NAT is not dependent upon HNO 3. Furthermore, in contrast to T NAT , T ACL is dependent upon the stratospheric sulfate aerosol loading and thus provides a means to estimate the impact on polar ozone of strong volcanic eruptions and some geo-engineering options, which are discussed. A parameterisation of T ACL is provided here, allowing it to be calculated for low solar elevation (or high solar zenith angle) over a comprehensive range of stratospheric conditions. Considering T ACL as a proxy for chlorine activation cannot replace a detailed model calculation, and polar ozone loss is influenced by other factors apart from the initial chlorine activation. However, T ACL provides a more accurate description of the temperature conditions necessary for chlorine activation and ozone loss in the polar stratosphere than T NAT .
The large burden of sulfate aerosols injected into the stratosphere by the eruption of Mount Pina... more The large burden of sulfate aerosols injected into the stratosphere by the eruption of Mount Pinatubo in 1991 cooled Earth and enhanced the destruction of polar ozone in the subsequent few years. The continuous injection of sulfur into the stratosphere has been suggested as a “geoengineering” scheme to counteract global warming. We use an empirical relationship between ozone depletion and chlorine activation to estimate how this approach might influence polar ozone. An injection of sulfur large enough to compensate for surface warming caused by the doubling of atmospheric CO 2 would strongly increase the extent of Arctic ozone depletion during the present century for cold winters and would cause a considerable delay, between 30 and 70 years, in the expected recovery of the Antarctic ozone hole.
Model simulations with the Chemical Lagrangian Model of the Stratosphere (CLaMS) driven by wind f... more Model simulations with the Chemical Lagrangian Model of the Stratosphere (CLaMS) driven by wind fields of the National Center for Environmental Prediction (NCEP) were performed in the midlatitude tropopause region in April 2008 to study two research flights conducted during the START08 campaign. One flight targeted a deep tropospheric intrusion and another flight targeted a deep stratospheric intrusion event, both of them in the vicinity of the subtropical and polar jet. Air masses with strong signatures of mixing between stratospheric and tropospheric air masses were identified from measured COO 3 correlations, and the characteristics were reproduced by CLaMS model simulations. CLaMS simulations in turn complement the observations and provide a broader view of the mixed region in physical space. Using artificial tracers of air mass origin within CLaMS yields unique information about the transport pathways and their contribution to the composition in the mixed region from different transport origins. Three different regions are examined to categorize dominant transport processes: (1) on the cyclonic side of the polar jet within tropopause folds where air from the lowermost stratosphere and the cyclonic side of the jet is transported downward into the troposphere, (2) on the anticyclonic side of the polar jet around the 2 PVU surface air masses, where signatures of mixing between the troposphere and lowermost stratosphere were found with large contributions of air masses from low latitudes, and (3) in the lower stratosphere associated with a deep tropospheric intrusion originating in the tropical tropopause layer (TTL). Moreover, the time scale of transport from the TTL into the lowermost stratosphere is in the range of weeks whereas the stratospheric intrusions occur on a time scale of days.
Journal of Geophysical Research: Atmospheres, 2004
During these validation balloon campaigns, CFC-12 was measured with the in situ instruments ASTRI... more During these validation balloon campaigns, CFC-12 was measured with the in situ instruments ASTRID, BONBON, and SAKURA and the remote sensing spectrometers MIPAS-B, FIRS-2, and MkIV. ILAS version 6.0 CFC-12 profiles obtained at the nearest location to the validation balloon measurement are compared with these validation balloon measurements. The quality of ILAS CFC-12 data processed with the version 6.0 algorithm improved significantly compared to previous versions. Low relative differences between ILAS CFC-12 and the correlative measurements of about 10% were found between 13 and 20 km. The comparison of vertical profiles shows that ILAS CFC-12 data are useful below about 20-22 km inside the vortex and below about 25 km outside the vortex. However, at greater altitudes the relative percentage difference increases very strongly with increasing altitude. Further, correlations of CFC-12 with N 2 O show a good agreement with the correlative measurements for N 2 O values of N 2 O > 150 ppbv. In summary, ILAS CFC-12 data are now suitable for scientific studies in the lower stratosphere.
Ozone depletion in the lower polar stratosphere is strongly dependent on the the amount of chlori... more Ozone depletion in the lower polar stratosphere is strongly dependent on the the amount of chlorine activation that is controlled by polar stratospheric cloud (PSC) occurrence and thus by temperature. We define a new measure, the PSC formation potential (PFP), suitable for assessing ozone depletion in both polar regions. In contrast to the previously defined volume of possible PSC existence (V PSC), this measure is normalized by the vortex volume in accordance with loss in column ozone averaged over the polar vortex and includes the lifetime of the vortices. Chemical ozone loss, derived between 1991 and 2005 for Arctic and Antarctic winters, correlates well with the PFP in the Arctic. In the Antarctic, chemical ozone loss is saturated. The year-to-year variation of the PFP for the Arctic has risen over the past thirty years with a maximum value in winter 2005. Accordingly, maximum chemical ozone loss has reached Antarctic loss values.
Recently, the cosmic-ray-driven electron-induced reaction mechanism (CRE) was introduced to expla... more Recently, the cosmic-ray-driven electron-induced reaction mechanism (CRE) was introduced to explain polar ozone depletion and surface temperature change. It was proposed that the dissociation of chlorofluorocarbons (CFCs) on ice surfaces of polar stratospheric clouds plays the dominant role in forming the ozone hole. Efforts have been made to predict polar ozone loss in future years. It was further proposed that CFCs and cosmic-ray-driven ozone depletion may control global surface temperatures. These assertions challenge the fundamental understanding of Antarctic stratospheric ozone loss and global warming. Here we show that these arguments based on the CRE mechanism are inconclusive. First, correlations of satellite data of CFC-12, N 2 O and CH 4 from ACE-FTS show no evidence of significant loss of CFC-12 as predicted by the CRE mechanism. Second, conclusions drawn about a possible CRE impact on the atmosphere, based on correlations of different observed atmospheric parameters, do not have a physical basis. Finally, predictions on the future development of the atmosphere based on these correlations are not reliable for either the ozone hole or global surface temperatures.
Using a combination of ozonesonde data and numerical simulations of the Chemical Lagrangian Model... more Using a combination of ozonesonde data and numerical simulations of the Chemical Lagrangian Model of the Stratosphere (CLaMS), the trend of tropospheric ozone (O 3) during 2002-2010 over Beijing was investigated. Tropospheric ozone over Beijing shows a winter minimum and a broad summer maximum with a clear positive trend in the maximum summer ozone concentration over the last decade. The observed significant trend of tropospheric column ozone is mainly caused by photochemical production (3.1 % yr −1 for a mean level of 52 DU). This trend is close to the significant trend of partial column ozone in the lower troposphere (0-3 km) resulting from the enhanced photochemical production during summer (3.0 % yr −1 for a mean level of 23 DU). Analysis of the CLaMS simulation shows that transport rather than chemistry drives most of the seasonality of tropospheric ozone. However, dynamical processes alone cannot explain the trend of tropospheric ozone in the observational data. Clearly enhanced ozone values and a negative vertical ozone gradient in the lower troposphere in the observational data emphasize the importance of photochemistry within the troposphere during spring and summer, and suggest that the photochemistry within the troposphere significantly contributes to the tropospheric ozone trend over Beijing during the last decade.
Ozone loss in the lower and middle stratosphere in spring and summer, in particular over polar re... more Ozone loss in the lower and middle stratosphere in spring and summer, in particular over polar regions, is driven mainly by halogens and nitrogen oxides (NO x). Whereas the stratospheric chlorine levels are expected to decrease in the future, the role of NO x for the O 3 budget in a changing climate is not well quantified. Here we combine satellite measurements and model simulations to diagnose the accumulated O 3 loss during winter and spring 2002-2003 in the Arctic polar stratosphere. We show that in a winter stratosphere strongly disturbed by warmings, O 3 loss processes driven by halogens and NO x can significantly overlap within the polar column and become comparable in magnitude even if a significant, halogen-induced O 3 loss has occurred. Whereas, until the beginning of March 2003, polar column O 3 loss was mainly caused by the halogen chemistry within the vortex at an altitude around 18 km, the chemical O 3 destruction in March and April was dominated by the NO x chemistry in O 3-rich air masses transported from the subtropics and mixed with the polar air above the region affected by the halogens. This NO x-related O 3 loss started around mid-December 2002 in subtropical air masses above 30 km that moved poleward after the major warming in January, descended to 22 km with an increasing magnitude of O 3 loss and reached surprisingly high values of up to 50% local loss around the end of April. To some extent, the NO x-driven O 3 loss was enhanced by mesospheric air trapped in the vortex at the beginning of the winter as a layer of few km in the vertical and transported downward within the vortex. The effect of NO x transported from the subtropics dominated the O 3 loss processes in the polar stratosphere in spring 2003, both relative to the effect of the halogens and relative to the contribution of the mesospheric NO x sources. A comparison with the 1999/2000 Arctic winter and with the Antarctic vortex split event in 2002 shows that wave events triggered by stratospheric warmings may significantly enhance O 3 loss driven by NO x when O 3-and NO x-rich air masses from the subtropics are transported poleward and are mixed with the vortex air.
Atmospheric Chemistry and Physics Discussions, 2014
Heterogeneous reactions in the Antarctic stratosphere are the cause of chlorine activation and oz... more Heterogeneous reactions in the Antarctic stratosphere are the cause of chlorine activation and ozone depletion, but the relative roles of different types of PSCs in chlorine activation is an open question. We use multi-year simulations of the chemistry-climate model EMAC to investigate the impact that the various types of PSCs have on Antarctic chlorine activation and ozone loss. <br><br> One standard and three sensitivity EMAC simulations have been performed. The results of these simulations show that the significance of heterogeneous reactions on NAT and ice particles, in comparison to liquid particles, is subordinate regarding chlorine activation and ozone depletion in Antarctic winter and spring. The heterogeneous chemistry on liquid particles is sufficient to activate at least 90% of the chlorine reservoir species. With the exception of the upper PSC regions between 10 and 30 hPa where temporarily the ice particles have a relevant contribution to the chlorine activa...
Atmospheric Chemistry and Physics Discussions, 2014
Here we present observations of the Cryogenic Infrared Spectrometers and Telescopes for the Atmos... more Here we present observations of the Cryogenic Infrared Spectrometers and Telescopes for the Atmosphere (CRISTA) of cirrus cloud and water vapour in August 1997 in the upper troposphere and lower stratosphere (UTLS) region. The observations indicate a considerable flux of moisture from the upper tropical troposphere into the extra-tropical lowermost stratosphere (LMS), resulting in the occurrence of high altitude optically thin cirrus clouds in the LMS. <br><br> The locations of the LMS cloud events observed by CRISTA are consistent with the tropopause height determined from coinciding radiosonde data. For a hemispheric analysis in tropopause relative coordinates an improved tropopause determination has been applied to the ECMWF temperature profiles. We found that a significant fraction of the cloud occurrences in the tropopause region are located in the LMS, even if a conservative overestimate of the cloud top height (CTH) determination by CRISTA of 500 m is assumed. The...
We report on a detailed time series analysis of long total column ozone (TO) records based on mul... more We report on a detailed time series analysis of long total column ozone (TO) records based on multi-satellite observations of daily resolution. We concentrate on three geographic latitudes over and around the Antarctic area, specifically on three circles at 58.5 ∘ S, 59.5 ∘ S, and 79.5 ∘ S. Almost continuous observations are available at the two former latitudes; however, data are lacking during the polar winter periods at 79.5 ∘ S, because the measurement technique requires sunlight. The methodology is motivated by level-crossing statistics, where subsets of the records above or below particular threshold levels are evaluated. Long-term trend reversal at around the turn of the century is already detectable for low TO levels in the raw time series in the "ozone-hole" region (79.5 ∘ S). In order to overcome the apparent non-stationarities of the time series, we determined daily TO differences (ΔTO) belonging to the same geographic longitudes between the different latitudinal circles. The result is a stable, stationary behavior for small (absolute) ΔTO values in the period January-February-March without any significant detectable trends. The high absolute value ΔTO subsets (September-October-November) indicate a robust trend reversal in the middle of the 1990s. The observed trend reversal in the total column ozone time series is consistent with the temporal development of the stratospheric halogen loading. However, a close correspondence of ozone and halogen turnaround years is not expected because of the statistical uncertainties in the determination of the ozone turnaround, and the many factors contributing to ozone depletion processes.
Dissociation induced by cosmic rays of chlorofluorocarbons (CFC) and HCl on the surfaces of polar... more Dissociation induced by cosmic rays of chlorofluorocarbons (CFC) and HCl on the surfaces of polar stratospheric clouds (PSC) has been suggested as playing a significant role in causing the ozone hole. However, observed stratospheric CFC distributions are inconsistent with a destruction of CFC on PSC surfaces and no significant correlation exists between ozone levels and cosmic-ray activity inside the polar regions. Model simulations indicate that this mechanism can have only a limited impact on chemical ozone loss and thus on the recovery of stratospheric ozone.
Ozone is one of the most important trace species in the atmosphere. Therefore, the history of res... more Ozone is one of the most important trace species in the atmosphere. Therefore, the history of research on ozone has also received a good deal of attention. Here a short overview of ozone research (with a focus on the stratosphere) is given, starting from the first atmospheric measurements and ending with current developments. It is valuable to study the history of ozone research, because much can be learned for current research from an understanding of how previous discoveries were made. Moreover, since the 1970s, the history of ozone research has also encompassed also the history of the human impact on the ozone layer and thus the history of policy measures taken to protect the ozone layer, notably the Montreal Protocol and its amendments and adjustments. The history of this development is particularly important because it may serve as a prototype for the development of policy measures for the protection of the Earth's climate. Zusammenfassung Ozon ist einer der wichtigsten Spurenstoffe in der Atmosphäre. Daher wurde auch der Geschichte der Ozonforschung viel Aufmerksamkeit gewidmet. Hier wird ein kurzerÜberblicküber die Ozonforschung gegeben (mit dem Fokus auf der Stratosphäre); beginnend mit den ersten atmosphärischen Ozonmessungen und endend mit aktuellen Entwicklungen. Das Studium der Geschichte der Ozonforschung ist hilfreich, da man für die aktuelle Forschung viel lernen kann, wenn man versteht, wie frühere Entdeckungen gemacht wurden. Seit den siebziger Jahren des vergangenen Jahrhunderts umfasst die Geschichte der Ozonforschung darüberhinaus die Geschichte des Einflusses des Menschen auf die Ozonschicht und damit auch die Geschichte der politischen Maßnahmen, die getroffen wurden, um die Ozonschicht zu schützen; vor allem das Montreal Protokoll sowie seine Anpassungen und Ergänzungen. Die Geschichte dieser Entwicklungen ist insbesonders von Bedeutung, da sie als Modell für die Entwicklung von politischen Maßnahmen zum Schutz des Klimas der Erde dienen kann.
The edge of the Arctic vortex constitutes a strong barrier to transport; however, the extent of i... more The edge of the Arctic vortex constitutes a strong barrier to transport; however, the extent of isolation of the vortex air as a function of altitude and season is relatively poorly quantified. In this study, by examining the transport of midlatitude air parcels across the vortex edge into the vortex, we analyze the permeability of the vortex edge. With the three-dimensional version of CLaMS (Chemical Lagrangian Model of the Stratosphere) we explore the dilution of the vortex air due to mixing in winter 1999-2000. An artificial, passive tracer was initialized on 1 December 1999 inside the polar vortex with a value of 100% and with a value of zero outside the polar vortex. Using several different definitions of the vortex edge, the resulting intrusions of midlatitude air into the vortex show the same mean features. This demonstrates that the diagnosed dilution does not strongly depend on the details of the definition of the vortex edge. At about the end of March 2000, the vertical structure of the vortex consisted of well-isolated, pure vortex layers around 500 K and 750 K, with some more diluted layers in between and at the vortex bottom. The influence of wave activity on the evolution of the intrusion layers is studied. The divergence of the Eliassen-Palm flux shows such a high variability during the whole period that it is not possible to assess a direct causality of certain intrusion layers and some specific patterns. Some characteristics of the vortex edge, in particular the shape of the gradient of potential vorticity (PV), can influence the dilution of the vortex. In cases without a distinct maximum in the PV gradient, the defined ''vortex edge'' may vary substantially from day to day. The comparison of some properties of the vortex (wind speed, PV field, area of the vortex, the maximum of the PV gradient) of undisturbed versus diluted layers and the variation in time of the intrusions were analyzed. All observed intrusions begin in conditions of weak PV gradient, indicating that the value of the maximum of the PV gradient may be used as a quantitative measure of the permeability of the vortex edge.
A recent paper [J. Chem. Phys.128, 041102 (2008)] reports resonant dissociative electron transfer... more A recent paper [J. Chem. Phys.128, 041102 (2008)] reports resonant dissociative electron transfer (RDET) to CCl4 in liquid ethanol. Part of the motivation for this work was the proposed importance of RDET processes for stratospheric ozone chemistry via dissociative electron attachment (DEA) triggered by cosmic ray activity in the polar winter stratosphere. In the present comment, it is argued that the relevance of DEA-induced destruction of chlorofluorocarbons (CFCs) in the polar stratosphere as a possible pathway for rapid chemical ozone destruction should not be a motivation for studies of DEA on CFC molecules; no correlation is observed between polar chemical ozone loss and cosmic ray activity. In any event, the relevance of this process as a key mechanism for the formation of the ozone hole should be presented as an issue debated in the scientific literature rather than as an established scientific fact.
Uncertainties in reactive uptake coefficients for pm 2 cm-a. For reaction R1 on NAT, the two sche... more Uncertainties in reactive uptake coefficients for pm 2 cm-a. For reaction R1 on NAT, the two schemes are in reactions involving HCI, CIONO2 and HOCI on nitric acid reasonable agreement at the ice frost point (2 hrs < r <7 trihydrate (N• and sulfuric acid tetrahydrate (SAT) are hrs), but differ substantially just below the NAT formation shown to affect modeled Arctic stratospheric ozone depletion temperature (1 day < r < 3 months). It is therefore under in a photochemical box model. The main contribution to the difference arises from the reaction ClONO• + HCl • Cl• + HNOa in early to midwinter. During this period, differences in predicted HCl and ClONO9• are more than 1 ppbv for several weeks when an upper limit for solid PSC existence is assumed. Ozone depletion is greater when liquid aerosols persist through the winter compared with cases where solid particles are assumed to form.
Satellite observations show that the enormous solar proton events (SPEs) in October-November 2003... more Satellite observations show that the enormous solar proton events (SPEs) in October-November 2003 had significant effects on the composition of the stratosphere and mesosphere in the polar regions. After the October-November 2003 SPEs and in early 2004, significant enhancements of NO x (=NO+NO 2) in the upper stratosphere and lower mesosphere in the Northern Hemisphere were observed by several satellite instruments. Here we present global full chemistry calculations performed with the CLaMS model to study the impact of mesospheric NO x intrusions on Arctic polar ozone loss processes in the stratosphere. Several model simulations are preformed with different upper boundary conditions for NO x at 2000 K potential temperature (≈50 km altitude). In our study we focus on the impact of the non-local production of NO x , which means the downward transport of enhanced NO x from the mesosphere to the stratosphere. The local production of NO x in the stratosphere is neglected. Our findings show that intrusions of mesospheric air into the stratosphere, transporting high burdens of NO x , affect the composition of the Arctic polar region down to about 400 K (≈17-18 km). We compare our simulated NO x and O 3 mixing ratios with satellite observations by ACE-FTS and MIPAS processed at IMK/IAA and derive an upper limit for the ozone loss caused by enhanced mesospheric NO x. Our findings show that in the Arctic polar vortex (equivalent lat.>70 • N) the accumulated column ozone loss between 350-2000 K potential temperature (≈14-50 km altitude) caused by the SPEs in October-November 2003 in the stratosphere is up to 3.3 DU with an upper limit of 5.5 DU until end of November. Further, we
1-year data sets of monthly averaged nitrous oxide (N 2 O) and ozone (O 3) derived from satellite... more 1-year data sets of monthly averaged nitrous oxide (N 2 O) and ozone (O 3) derived from satellite measurements were used as a tool for the evaluation of atmospheric photochemical models. Two 1-year data sets, one solar occultation data set derived from the Improved Limb Atmospheric Spectrometer (ILAS and ILAS-II) and one limb sounding data set derived from the Odin Sub-Millimetre Radiometer (Odin/SMR) were employed. Here, these data sets are used for the evaluation of two Chemical Transport Models (CTMs), the Karlsruhe Simulation Model of the Middle Atmosphere (KASIMA) and the Chemical Lagrangian Model of the Stratosphere (CLaMS) as well as for one Chemistry-Climate Model (CCM), the atmospheric chemistry general circulation model ECHAM5/MESSy1 (E5M1) in the lower stratosphere with focus on the Northern Hemisphere. Since the Odin/SMR measurements cover the entire hemisphere, the evaluation is performed for the entire hemisphere as well as for the low latitudes, midlatitudes and high latitudes using the Odin/SMR 1-year data set as reference. To assess the impact of using different data sets for such an evaluation study we repeat the evaluation for the polar lower stratosphere using the ILAS/ILAS-II data set. Only small differences were found using ILAS/ILAS-II instead of Odin/SMR as a reference, thus, showing that the results are not influenced by the particular satellite data set used for the evaluation. The evalu
Low stratospheric temperatures are known to be responsible for heterogeneous chlorine activation ... more Low stratospheric temperatures are known to be responsible for heterogeneous chlorine activation that leads to polar ozone depletion. Here, we discuss the temperature threshold below which substantial chlorine activation occurs. We suggest that the onset of chlorine activation is dominated by reactions on cold binary aerosol particles, without the formation of polar stratospheric clouds (PSCs), i.e. without any significant uptake of HNO 3 from the gas phase. Using reaction rates on cold binary aerosol in a model of stratospheric chemistry, a chlorine activation threshold temperature, T ACL , is derived. At typical stratospheric conditions, T ACL is similar in value to T NAT (within 1-2 K), the highest temperature at which nitric acid trihydrate (NAT) can exist. T NAT is still in use to parameterise the threshold temperature for the onset of chlorine activation. However, perturbations can cause T ACL to differ from T NAT : T ACL is dependent upon H 2 O and potential temperature, but unlike T NAT is not dependent upon HNO 3. Furthermore, in contrast to T NAT , T ACL is dependent upon the stratospheric sulfate aerosol loading and thus provides a means to estimate the impact on polar ozone of strong volcanic eruptions and some geo-engineering options, which are discussed. A parameterisation of T ACL is provided here, allowing it to be calculated for low solar elevation (or high solar zenith angle) over a comprehensive range of stratospheric conditions. Considering T ACL as a proxy for chlorine activation cannot replace a detailed model calculation, and polar ozone loss is influenced by other factors apart from the initial chlorine activation. However, T ACL provides a more accurate description of the temperature conditions necessary for chlorine activation and ozone loss in the polar stratosphere than T NAT .
The large burden of sulfate aerosols injected into the stratosphere by the eruption of Mount Pina... more The large burden of sulfate aerosols injected into the stratosphere by the eruption of Mount Pinatubo in 1991 cooled Earth and enhanced the destruction of polar ozone in the subsequent few years. The continuous injection of sulfur into the stratosphere has been suggested as a “geoengineering” scheme to counteract global warming. We use an empirical relationship between ozone depletion and chlorine activation to estimate how this approach might influence polar ozone. An injection of sulfur large enough to compensate for surface warming caused by the doubling of atmospheric CO 2 would strongly increase the extent of Arctic ozone depletion during the present century for cold winters and would cause a considerable delay, between 30 and 70 years, in the expected recovery of the Antarctic ozone hole.
Model simulations with the Chemical Lagrangian Model of the Stratosphere (CLaMS) driven by wind f... more Model simulations with the Chemical Lagrangian Model of the Stratosphere (CLaMS) driven by wind fields of the National Center for Environmental Prediction (NCEP) were performed in the midlatitude tropopause region in April 2008 to study two research flights conducted during the START08 campaign. One flight targeted a deep tropospheric intrusion and another flight targeted a deep stratospheric intrusion event, both of them in the vicinity of the subtropical and polar jet. Air masses with strong signatures of mixing between stratospheric and tropospheric air masses were identified from measured COO 3 correlations, and the characteristics were reproduced by CLaMS model simulations. CLaMS simulations in turn complement the observations and provide a broader view of the mixed region in physical space. Using artificial tracers of air mass origin within CLaMS yields unique information about the transport pathways and their contribution to the composition in the mixed region from different transport origins. Three different regions are examined to categorize dominant transport processes: (1) on the cyclonic side of the polar jet within tropopause folds where air from the lowermost stratosphere and the cyclonic side of the jet is transported downward into the troposphere, (2) on the anticyclonic side of the polar jet around the 2 PVU surface air masses, where signatures of mixing between the troposphere and lowermost stratosphere were found with large contributions of air masses from low latitudes, and (3) in the lower stratosphere associated with a deep tropospheric intrusion originating in the tropical tropopause layer (TTL). Moreover, the time scale of transport from the TTL into the lowermost stratosphere is in the range of weeks whereas the stratospheric intrusions occur on a time scale of days.
Journal of Geophysical Research: Atmospheres, 2004
During these validation balloon campaigns, CFC-12 was measured with the in situ instruments ASTRI... more During these validation balloon campaigns, CFC-12 was measured with the in situ instruments ASTRID, BONBON, and SAKURA and the remote sensing spectrometers MIPAS-B, FIRS-2, and MkIV. ILAS version 6.0 CFC-12 profiles obtained at the nearest location to the validation balloon measurement are compared with these validation balloon measurements. The quality of ILAS CFC-12 data processed with the version 6.0 algorithm improved significantly compared to previous versions. Low relative differences between ILAS CFC-12 and the correlative measurements of about 10% were found between 13 and 20 km. The comparison of vertical profiles shows that ILAS CFC-12 data are useful below about 20-22 km inside the vortex and below about 25 km outside the vortex. However, at greater altitudes the relative percentage difference increases very strongly with increasing altitude. Further, correlations of CFC-12 with N 2 O show a good agreement with the correlative measurements for N 2 O values of N 2 O > 150 ppbv. In summary, ILAS CFC-12 data are now suitable for scientific studies in the lower stratosphere.
Ozone depletion in the lower polar stratosphere is strongly dependent on the the amount of chlori... more Ozone depletion in the lower polar stratosphere is strongly dependent on the the amount of chlorine activation that is controlled by polar stratospheric cloud (PSC) occurrence and thus by temperature. We define a new measure, the PSC formation potential (PFP), suitable for assessing ozone depletion in both polar regions. In contrast to the previously defined volume of possible PSC existence (V PSC), this measure is normalized by the vortex volume in accordance with loss in column ozone averaged over the polar vortex and includes the lifetime of the vortices. Chemical ozone loss, derived between 1991 and 2005 for Arctic and Antarctic winters, correlates well with the PFP in the Arctic. In the Antarctic, chemical ozone loss is saturated. The year-to-year variation of the PFP for the Arctic has risen over the past thirty years with a maximum value in winter 2005. Accordingly, maximum chemical ozone loss has reached Antarctic loss values.
Recently, the cosmic-ray-driven electron-induced reaction mechanism (CRE) was introduced to expla... more Recently, the cosmic-ray-driven electron-induced reaction mechanism (CRE) was introduced to explain polar ozone depletion and surface temperature change. It was proposed that the dissociation of chlorofluorocarbons (CFCs) on ice surfaces of polar stratospheric clouds plays the dominant role in forming the ozone hole. Efforts have been made to predict polar ozone loss in future years. It was further proposed that CFCs and cosmic-ray-driven ozone depletion may control global surface temperatures. These assertions challenge the fundamental understanding of Antarctic stratospheric ozone loss and global warming. Here we show that these arguments based on the CRE mechanism are inconclusive. First, correlations of satellite data of CFC-12, N 2 O and CH 4 from ACE-FTS show no evidence of significant loss of CFC-12 as predicted by the CRE mechanism. Second, conclusions drawn about a possible CRE impact on the atmosphere, based on correlations of different observed atmospheric parameters, do not have a physical basis. Finally, predictions on the future development of the atmosphere based on these correlations are not reliable for either the ozone hole or global surface temperatures.
Using a combination of ozonesonde data and numerical simulations of the Chemical Lagrangian Model... more Using a combination of ozonesonde data and numerical simulations of the Chemical Lagrangian Model of the Stratosphere (CLaMS), the trend of tropospheric ozone (O 3) during 2002-2010 over Beijing was investigated. Tropospheric ozone over Beijing shows a winter minimum and a broad summer maximum with a clear positive trend in the maximum summer ozone concentration over the last decade. The observed significant trend of tropospheric column ozone is mainly caused by photochemical production (3.1 % yr −1 for a mean level of 52 DU). This trend is close to the significant trend of partial column ozone in the lower troposphere (0-3 km) resulting from the enhanced photochemical production during summer (3.0 % yr −1 for a mean level of 23 DU). Analysis of the CLaMS simulation shows that transport rather than chemistry drives most of the seasonality of tropospheric ozone. However, dynamical processes alone cannot explain the trend of tropospheric ozone in the observational data. Clearly enhanced ozone values and a negative vertical ozone gradient in the lower troposphere in the observational data emphasize the importance of photochemistry within the troposphere during spring and summer, and suggest that the photochemistry within the troposphere significantly contributes to the tropospheric ozone trend over Beijing during the last decade.
Ozone loss in the lower and middle stratosphere in spring and summer, in particular over polar re... more Ozone loss in the lower and middle stratosphere in spring and summer, in particular over polar regions, is driven mainly by halogens and nitrogen oxides (NO x). Whereas the stratospheric chlorine levels are expected to decrease in the future, the role of NO x for the O 3 budget in a changing climate is not well quantified. Here we combine satellite measurements and model simulations to diagnose the accumulated O 3 loss during winter and spring 2002-2003 in the Arctic polar stratosphere. We show that in a winter stratosphere strongly disturbed by warmings, O 3 loss processes driven by halogens and NO x can significantly overlap within the polar column and become comparable in magnitude even if a significant, halogen-induced O 3 loss has occurred. Whereas, until the beginning of March 2003, polar column O 3 loss was mainly caused by the halogen chemistry within the vortex at an altitude around 18 km, the chemical O 3 destruction in March and April was dominated by the NO x chemistry in O 3-rich air masses transported from the subtropics and mixed with the polar air above the region affected by the halogens. This NO x-related O 3 loss started around mid-December 2002 in subtropical air masses above 30 km that moved poleward after the major warming in January, descended to 22 km with an increasing magnitude of O 3 loss and reached surprisingly high values of up to 50% local loss around the end of April. To some extent, the NO x-driven O 3 loss was enhanced by mesospheric air trapped in the vortex at the beginning of the winter as a layer of few km in the vertical and transported downward within the vortex. The effect of NO x transported from the subtropics dominated the O 3 loss processes in the polar stratosphere in spring 2003, both relative to the effect of the halogens and relative to the contribution of the mesospheric NO x sources. A comparison with the 1999/2000 Arctic winter and with the Antarctic vortex split event in 2002 shows that wave events triggered by stratospheric warmings may significantly enhance O 3 loss driven by NO x when O 3-and NO x-rich air masses from the subtropics are transported poleward and are mixed with the vortex air.
Atmospheric Chemistry and Physics Discussions, 2014
Heterogeneous reactions in the Antarctic stratosphere are the cause of chlorine activation and oz... more Heterogeneous reactions in the Antarctic stratosphere are the cause of chlorine activation and ozone depletion, but the relative roles of different types of PSCs in chlorine activation is an open question. We use multi-year simulations of the chemistry-climate model EMAC to investigate the impact that the various types of PSCs have on Antarctic chlorine activation and ozone loss. <br><br> One standard and three sensitivity EMAC simulations have been performed. The results of these simulations show that the significance of heterogeneous reactions on NAT and ice particles, in comparison to liquid particles, is subordinate regarding chlorine activation and ozone depletion in Antarctic winter and spring. The heterogeneous chemistry on liquid particles is sufficient to activate at least 90% of the chlorine reservoir species. With the exception of the upper PSC regions between 10 and 30 hPa where temporarily the ice particles have a relevant contribution to the chlorine activa...
Atmospheric Chemistry and Physics Discussions, 2014
Here we present observations of the Cryogenic Infrared Spectrometers and Telescopes for the Atmos... more Here we present observations of the Cryogenic Infrared Spectrometers and Telescopes for the Atmosphere (CRISTA) of cirrus cloud and water vapour in August 1997 in the upper troposphere and lower stratosphere (UTLS) region. The observations indicate a considerable flux of moisture from the upper tropical troposphere into the extra-tropical lowermost stratosphere (LMS), resulting in the occurrence of high altitude optically thin cirrus clouds in the LMS. <br><br> The locations of the LMS cloud events observed by CRISTA are consistent with the tropopause height determined from coinciding radiosonde data. For a hemispheric analysis in tropopause relative coordinates an improved tropopause determination has been applied to the ECMWF temperature profiles. We found that a significant fraction of the cloud occurrences in the tropopause region are located in the LMS, even if a conservative overestimate of the cloud top height (CTH) determination by CRISTA of 500 m is assumed. The...
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Papers by Rolf Müller