Ozone loss pathways and their rates in the ozone quasi-biennial oscillation (QBO), which is simulated by a chemistry-climate model developed by the Meteorological Research Institute of Japan, are ...evaluated using an objective pathway analysis program (PAP). The analyzed chemical system contains catalytic cycles caused by NOx, HOx, ClOx, Ox, and BrOx. PAP quantified the rates of all significant catalytic ozone loss cycles, and evaluated the partitioning among these cycles. The QBO amplitude of the sum of all cycles amounts to about 4 and 14 % of the annual mean of the total ozone loss rate at 10 and 20 hPa, respectively. The contribution of catalytic cycles to the QBO of the ozone loss rate is found to be as follows: NOx cycles contribute the largest fraction (50–85 %) of the QBO amplitude of the total ozone loss rate; HOx cycles are the second-largest (20–30 %) below 30 hPa and the third-largest (about 10 %) above 20 hPa; Ox cycles rank third (5–20 %) below 30 hPa and second (about 20 %) above 20 hPa; ClOx cycles rank fourth (5–10 %); and BrOx cycles are almost negligible. The relative contribution of the NOx and Ox cycles to the QBO amplitude of ozone loss differs by up to 10 % and 20 %, respectively, from their contribution to the annual mean ozone loss rate. The ozone QBO at 20 hPa is mainly driven by ozone transport, which then alters the ozone loss rate. In contrast, the ozone QBO at 10 hPa is driven chemically by NOx and the temperature dependence of O/O3, which results from the temperature dependence of the reaction O + O2 + M → O 3 + M. In addition, the ozone QBO at 10 hPa is influenced by the overhead ozone column, which affects O/O3 (through ozone photolysis) and the ozone production rate (through oxygen photolysis).
Context. The first opportunity to detect indications for life outside of the Solar System may be provided already within the next decade with upcoming missions such as the James Webb Space Telescope ...(JWST), the European Extremely Large Telescope (E-ELT) and the Atmospheric Remote-sensing Infrared Exoplanet Large-survey (ARIEL) mission, searching for atmospheric biosignatures on planets in the habitable zone of cool K- and M-stars. Nevertheless, their harsh stellar radiation and particle environment could lead to photochemical loss of atmospheric biosignatures. Aims. We aim to study the influence of cosmic rays on exoplanetary atmospheric biosignatures and the radiation environment considering feedbacks between energetic particle precipitation, climate, atmospheric ionization, neutral and ion chemistry, and secondary particle generation. Methods. We describe newly combined state-of-the-art modeling tools to study the impact of the radiation and particle environment, in particular of cosmic rays, on atmospheric particle interaction, atmospheric chemistry, and the climate-chemistry coupling in a self-consistent model suite. To this end, models like the Atmospheric Radiation Interaction Simulator (AtRIS), the Exoplanetary Terrestrial Ion Chemistry model (ExoTIC), and the updated coupled climate-chemistry model are combined. Results. In addition to comparing our results to Earth-bound measurements, we investigate the ozone production and -loss cycles as well as the atmospheric radiation dose profiles during quiescent solar periods and during the strong solar energetic particle event of February 23, 1956. Further, the scenario-dependent terrestrial transit spectra, as seen by the NIR-Spec infrared spectrometer onboard the JWST, are modeled. Amongst others, we find that the comparatively weak solar event drastically increases the spectral signal of HNO3, while significantly suppressing the spectral feature of ozone. Because of the slow recovery after such events, the latter indicates that ozone might not be a good biomarker for planets orbiting stars with high flaring rates.
In climate modeling, the stratospheric ozone layer is typically only considered in a highly simplified form due to computational constraints. For climate projections, it would be of advantage to ...include the mutual interactions between stratospheric ozone, temperature, and atmospheric dynamics to accurately represent radiative forcing. The overarching goal of our research is to replace the ozone layer in climate models with a machine-learned neural representation of the stratospheric ozone chemistry that allows for a particularly fast, but accurate and stable simulation. We created a benchmark data set from pairs of input and output variables that we stored from simulations of the ATLAS Chemistry and Transport Model. We analyzed several variants of multilayer perceptrons suitable for physical problems to learn a neural representation of a function that predicts 24-h ozone tendencies based on input variables. We performed a comprehensive hyperparameter optimization of the multilayer perceptron using Bayesian search and Hyperband early stopping. We validated our model by replacing the full chemistry module of ATLAS and comparing computation time, accuracy, and stability. We found that our model had a computation time that was a factor of 700 faster than the full chemistry module. The accuracy of our model compares favorably to the full chemistry module within a 2-year simulation run, also outperforms a previous polynomial approach for fast ozone chemistry, and reproduces seasonality well in both hemispheres. In conclusion, the neural representation of stratospheric ozone chemistry in simulation resulted in an ozone layer that showed a high accuracy, significant speed-up, and stability in a long-term simulation.
•Determination of all significant O3 producing and consuming pathways and quantification of their contributions in the Martian atmosphere with help of an automated computer algorithm.•O3 production ...results from CO2 and O2 photolysis.•O3 is consumed by catalytic cycles involving HOx (= H + OH + HO2).•The Martian atmosphere can be divided into two chemically distinct re- gions according to the O(3P):O3 ratio.•Vertical transport of O(3P) from upper layers downwards into the O3 layer at around 50 km altitude provides an additional source of Ox (= O + O3), which is pivotal to the formation of the Martian O3 volume mixing ratio maximum.
Atmospheric chemical composition is crucial in determining a planet’s atmospheric structure, stability, and evolution. Attaining a quantitative understanding of the essential chemical mechanisms governing atmospheric composition is nontrivial due to complex interactions between chemical species. Trace species, for example, can participate in catalytic cycles – affecting the abundance of major and other trace gas species. Specifically, for Mars, such cycles dictate the abundance of its primary atmospheric constituent, carbon dioxide (CO2), but also for one of its trace gases, ozone (O3). The identification of chemical pathways/cycles by hand is extremely demanding; hence, the application of numerical methods, such as the Pathway Analysis Program (PAP), is crucial to analyze and quantitatively exemplify chemical reaction networks. Here, we carry out the first automated quantitative chemical pathway analysis of Mars’ atmosphere with respect to O3. PAP was applied to JPL/Caltech’s 1-D updated photochemical Mars model’s output data. We determine all significant chemical pathways and their contribution to O3 production and consumption (up to 80 km) in order to investigate the mechanisms causing the characteristic shape of the O3 volume mixing ratio profile, i.e. a ground layer maximum and an ozone layer at ∼50 km. These pathways explain why an O3 layer is present, why it is located at that particular altitude and what the different processes forming the near-surface and middle atmosphere O3 maxima are. Furthermore, we show that the Martian atmosphere can be divided into two chemically distinct regions according to the O(3P):O3 ratio. In the lower region (below approximately 24 km altitude) O3 is the most abundant Ox (= O3 + O(3P)) species. In the upper region (above approximately 24 km altitude), where the O3 layer is located, O(3P) is the most abundant Ox species. Earlier results concerning the formation of O3 on Mars can now be explained with the help of chemical pathways leading to a better understanding of the vertical O3 profile.
Recently, it was shown that of the ozone‐depleting substances currently emitted, N2O emissions (the primary source of stratospheric NOx) dominate, and are likely to do so throughout the 21st century. ...To investigate the links between N2O and NOx concentrations, and the effects of NOxon ozone in a changing climate, the evolution of stratospheric ozone from 1960 to 2100 was simulated using the NIWA‐SOCOL chemistry‐climate model. The yield of NOx from N2O is reduced due to stratospheric cooling and a strengthening of the Brewer‐Dobson circulation. After accounting for the reduced NOx yield, additional weakening of the primary NOxcycle is attributed to reduced availability of atomic oxygen, due to a) stratospheric cooling decreasing the atomic oxygen/ozone ratio, and b) enhanced rates of chlorine‐catalyzed ozone loss cycles around 2000 and enhanced rates of HOx‐induced ozone depletion. Our results suggest that the effects of N2O on ozone depend on both the radiative and chemical environment of the upper stratosphere, specifically CO2‐induced cooling of the stratosphere and elevated CH4 emissions which enhance HOx‐induced ozone loss and remove the availability of atomic oxygen to participate in NOx ozone loss cycles.
Key Points
NOx‐induced ozone destruction slows through the 21st century
Due to chemical, radiative and dynamical changes in the stratosphere
The effectiveness of N2O as an ODS is weakened by elevated CH4 concentrations
The maintenance of large concentrations of active chlorine in Antarctic spring allows strong chemical ozone destruction to occur. In the lower stratosphere (approximately 16-18 km, 85-55 hPa, 390-430 ...K) in the core of the polar vortex, high levels of active chlorine are maintained, although rapid gas-phase production of HCl occurs. The maintenance is achieved through HCl null cycles in which the HCl production is balanced by immediate reactivation. The chemistry of the methyl peroxy radical (CH
3
O
2
) is essential for these HCl null cycles and thus for Antarctic chlorine and ozone loss chemistry in the lower stratosphere in the core of the polar vortex. The key reaction here is the reaction
; this reaction should not be neglected in simulations of polar ozone loss. Here we investigate the full chemistry of CH
3
O
2
in box-model simulations representative for the conditions in the core of the polar vortex in the lower stratosphere. These simulations include the reaction CH
3
O
2
+ Cl, the product methylhypochlorite (CH
3
OCl) of the reaction CH
3
O
2
+ ClO, and the subsequent chemical decomposition of CH
3
OCl. We find that when the formation of CH
3
OCl is taken into account, it is important that also the main loss channels for CH
3
OCl, namely photolysis and reaction with Cl are considered. Provided that this is the case, there is only a moderate impact of the formation of CH
3
OCl in the reaction CH
3
O
2
+ ClO on polar chlorine chemistry in our simulations. Simulated peak mixing ratios of CH
3
OCl (
ppb) occur at the time of the lowest ozone mixing ratios. Further, our model simulations indicate that the reaction CH
3
O
2
+ Cl does not have a strong impact on polar chlorine chemistry. During the period of the lowest ozone concentrations in late September, enhanced values of CH
3
O
2
are simulated and, as a consequence, also enhanced values of formaldehyde (about 100 ppt) and methanol (about 5 ppt).
Ozone loss pathways and their rates in the ozone quasi-biennial oscillation (QBO) simulated by a chemistry-climate model of the Meteorological Research Institute of Japan are evaluated by using an ...objective pathway analysis program (PAP). The analyzed chemical system contains catalytic cycles due to NOx, HOx, ClOx, Ox, and BrOx. PAP quantified the rates of all significant catalytic ozone loss cycles, and evaluated the partitioning among these cycles. The QBO amplitude of the sum of all cycles amounts to about 4 and 14 % of the annual mean of the total ozone loss rate at 10 and 20 hPa, respectively. The contribution of catalytic cycles to the QBO of the ozone loss rate is found to be as follows: NOx cycles contribute the largest fraction (50-85 %) of the QBO amplitude of the total ozone loss rate; HOx cycles are the second-largest (20-30 %) below 30 hPa and the third-largest (about 10 %) above 20 hPa; Ox cycles rank third (5-20 %) below 30 hPa and second (about 20 %) above 20 hPa; ClOx cycles rank fourth (5-10 %); and BrOx cycles are almost negligible. The relative contribution of the NOx and Ox cycles to the QBO amplitude of ozone loss differs by up to 10 and 20 %, respectively, from their contribution to the annual-mean ozone loss rate. The ozone QBO at 20 hPa is mainly driven by ozone transport, which then affects the ozone loss rate. In contrast, the ozone QBO at 10 hPa is driven chemically mainly by NOx and the temperature dependence of O/O3, which results from the temperature dependence of the reaction O + O2 + M → O3 + M. In addition, the ozone QBO at 10 hPa is influenced by the overhead ozone column, which affects O/O3 (through ozone photolysis) and the ozone production rate (through oxygen photolysis).
► The first automated quantified chemical pathway analysis of the martian atmosphere with respect to CO2 is presented. ► All dominant pathways related to CO2-production have been quantified as a ...function of altitude. ► Their contributions to the atmospheric CO2 abundance of individual pathways vary considerably with altitude. ► Results endorse the importance of transport processes in governing the stability of CO2 in the martian atmosphere. ► An unknown chemical pathway contributing approximately 8% to global CO2-production has been identified.
The chemical composition of a planetary atmosphere plays an important role for atmospheric structure, stability, and evolution. Potentially complex interactions between chemical species do not often allow for an easy understanding of the underlying chemical mechanisms governing the atmospheric composition. In particular, trace species can affect the abundance of major species by acting in catalytic cycles. On Mars, such cycles even control the abundance of its main atmospheric constituent CO2. The identification of catalytic cycles (or more generally chemical pathways) by hand is quite demanding. Hence, the application of computer algorithms is beneficial in order to analyze complex chemical reaction networks. Here, we have performed the first automated quantified chemical pathways analysis of the Martian atmosphere with respect to CO2-production in a given reaction system. For this, we applied the Pathway Analysis Program (PAP) to output data from the Caltech/JPL photochemical Mars model. All dominant chemical pathways directly related to the global CO2-production have been quantified as a function of height up to 86km. We quantitatively show that CO2-production is dominated by chemical pathways involving HOx and Ox. In addition, we find that NOx in combination with HOx and Ox exhibits a non-negligible contribution to CO2-production, especially in Mars’ lower atmosphere. This study reveals that only a small number of chemical pathways contribute significantly to the atmospheric abundance of CO2 on Mars; their contributions to CO2-production vary considerably with altitude. This analysis also endorses the importance of transport processes in governing CO2-stability in the Martian atmosphere. Lastly, we identify a previously unknown chemical pathway involving HOx, Ox, and HO2-photodissociation, contributing 8% towards global CO2-production by chemical pathways using recommended up-to-date values for reaction rate coefficients.
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