Reduction of Stratospheric Ozone by Nitrogen Oxide Catalysts from Supersonic Transport Exhaust

A Revisit of Large-Scale Patterns in Middle Stratospheric Circulation Variations

Variations in stratospheric atmospheric circulation significantly impact tropospheric weather and climate. Understanding these variations not only aids in better prediction of tropospheric weather and climate but also provides guidance for the development and flight trajectories of stratospheric aircraft. Our understanding of the stratosphere has made remarkable progress over the past 100 years. However, we still lack a comprehensive perspective on large-scale patterns in stratospheric circulation, as the stratosphere is a typical complex system. To address this gap, we employed the eigen microstate approach (EMA) to revisit the characteristics of zonal wind from 70-10 hPa from 1980 to 2022, based on ERA5 reanalysis data. Our analysis focused on the three leading modes, corresponding to variations in the strength of the quasi-biennial oscillation (QBO) and the stratospheric atmospheric circulations in the Arctic and Antarctic, respectively. After filtering out high-frequency components from the temporal evolutions of these modes, a significant 11-year cycle was observed in the Antarctic stratospheric atmospheric circulation mode, potentially linked to the 11-year solar cycle. In contrast, the Arctic stratospheric atmospheric circulation mode showed a 5-6-year cycle without evidence of an 11-year periodicity. This difference is likely due to the timing of polar vortex breakdowns: the Antarctic polar vortex breaks up later, experiencing its greatest variability in late spring and early summer, making it more susceptible to solar radiation effects, unlike the Arctic polar vortex, which peaks in winter and early spring. The fourth mode exhibits characteristics of a Southern Hemisphere dipole and shows a significant correlation with the Antarctic stratospheric atmospheric circulation mode, leading it by about two months. We designed a linear prediction model that successfully demonstrated its predictive capability for the Antarctic polar vortex.

Enrichment and characterization of a nitric oxide-reducing microbial community in a continuous bioreactor

Nitric oxide (NO) is a highly reactive and climate-active molecule and a key intermediate in the microbial nitrogen cycle. Despite its role in the evolution of denitrification and aerobic respiration, high redox potential and capacity to sustain microbial growth, our understanding of NO-reducing microorganisms remains limited due to the absence of NO-reducing microbial cultures obtained directly from the environment using NO as a substrate. Here, using a continuous bioreactor and a constant supply of NO as the sole electron acceptor, we enriched and characterized a microbial community dominated by two previously unknown microorganisms that grow at nanomolar NO concentrations and survive high amounts (>6 µM) of this toxic gas, reducing it to N2 with little to non-detectable production of the greenhouse gas nitrous oxide. These results provide insight into the physiology of NO-reducing microorganisms, which have pivotal roles in the control of climate-active gases, waste removal, and evolution of nitrate and oxygen respiration.

A Quantum Chemical Investigation into the Molecular Mechanism of the Atmospheric Reactions of Chemi-Ions with Nitrogen and Nitrogen Oxides

Nitrogen oxides and chemi-ions are atmospheric pollutants with considerable aeronomic interest. These toxicants can react with each other, producing various ionic species and highly reactive by-products that play a crucial role in aerosol clustering and mediate several important atmospheric reactions. Understanding the chemical reactivity of these pollutants can provide essential information for controlling their excess emission into the atmosphere. Computational modeling and electronic structure studies help in predicting the structure, reactivity, and thermodynamics of transient atmospheric chemical species and can guide experimental research by providing vital mechanistic insights and data. In the present study, a computational investigation into the mechanisms of the binary associative reactions between negative ions: O₂^- and O₃^- with NO, NO₂, and N₂ was conducted using the Coupled-Cluster Singles and Doubles (CCSD) theory. Five model reactions between N₂/NO_x with O_n^- (n = 2, 3) were considered in this work. Our calculations revealed that reactions (2) and (5) are two sequential processes involving intermediates, and all others occur in a concerted manner by direct transitions from the reactants to the products, with no isolable intermediates proceeding via single non-planar transition states. Our study revealed that the higher activation barrier required for the formation of NO₃^- (2) as compared to NO₂^- (1) could be the reason for the excess formation of NO₂^- ions over NO₃^- ions in the atmosphere. Further, all the investigated reactions except (5) are found to be feasible at room temperature. The energy required to break N-N bonds in the N₂ molecule justifies the high barrier for (5). The results obtained from the study are in close agreement with the available experimental data. Moreover, the data from the study can be utilized for the evaluation of experiments and model predictions pertaining to NOx oxidation and molecular modeling of the gas-phase chemistry of pollutants/nucleation precursors formed in the Earth's atmosphere and aircraft engines.

Inoculation effect of Pseudomonas sp. TF716 on N2O emissions during rhizoremediation of diesel-contaminated soil

The demand for rhizoremediation technology that can minimize greenhouse gas emissions while effectively removing pollutants in order to mitigate climate change has increased. The inoculation effect of N₂O-reducing Pseudomonas sp. TF716 on N₂O emissions and on remediation performance during the rhizoremediation of diesel-contaminated soil planted with tall fescue (Festuca arundinacea) or maize (Zea mays) was investigated. Pseudomonas sp. TF716 was isolated from the rhizosphere soil of tall fescue. The maximum N₂O reduction rate of TF716 was 18.9 mmol N₂O g dry cells⁻¹ h⁻¹, which is superior to the rates for previously reported Pseudomonas spp. When Pseudomonas sp. TF716 was added to diesel-contaminated soil planted with tall fescue, the soil N₂O-reduction potential was 2.88 times higher than that of soil with no inoculation during the initial period (0–19 d), and 1.08–1.13 times higher thereafter. However, there was no enhancement in the N₂O-reduction potential for the soil planted with maize following inoculation with strain TF716. In addition, TF716 inoculation did not significantly affect diesel degradation during rhizoremediation, suggesting that the activity of those microorganisms involved in diesel degradation was unaffected by TF716 treatment. Analysis of the dynamics of the bacterial genera associated with N₂O reduction showed that Pseudomonas had the highest relative abundance during the rhizoremediation of diesel-contaminated soil planted with tall fescue and treated with strain TF716. Overall, these results suggest that N₂O emissions during the rhizoremediation of diesel-contaminated soil using tall fescue can be reduced with the addition of Pseudomonas sp. TF716.

The effect of (H2O)n (n = 1-3) clusters on the reaction of HONO with HCl: a mechanistic and kinetic study

The reaction between HONO and HCl is a possible pathway for the generation of ClNO, which is prone to photolyze, produce chlorine radicals, and accelerate the oxidation of tropospheric VOCs. Current experimental and theoretical studies have significant differences in rate constants under similar conditions. This study aims to examine the reasons for this difference. In this study, the effects of a single water molecule, water dimer, water trimer, excess HCl and excess HONO on the reaction mechanism of HONO + HCl were studied at the CCSD(T)/aug-cc-pVTZ//M06-2X/6-311+G(2df,2p) level and the rate constants of each reaction channel were calculated. Our results showed that the reaction potential barrier of HONO with HCl was the lowest only when the water dimer was present, and the reaction rate constants were close to the experimental results, and both the cis-HONO⋯(H₂O)₂ + HCl and the trans-HONO⋯(H₂O)₂ + HCl reaction paths are likely to occur. We think that the reason for the inconsistency between experimental and theoretical results is that the water dimer is involved in the reaction in experiments.

Review: The Effects of Supersonic Aviation on Ozone and Climate

When working towards regulation of supersonic aviation, a comprehensive understanding of the global climate effect of supersonic aviation is required in order to develop future regulatory issues. Such research requires a comprehensive overview of existing scientific literature having explored the climate effect of aviation. This review article provides an overview on earlier studies assessing the climate effects of supersonic aviation, comprising non-CO2 effects. An overview on the historical evaluation of research focussing on supersonic aviation and its environmental impacts is provided, followed by an overview on concepts explored and construction of emission inventories. Quantitative estimates provided for individual effects are presented and compared. Subsequently, regulatory issues related to supersonic transport are summarised. Finally, requirements for future studies, e.g., in emission scenario construction or numerical modelling of climate effects, are summarised and main conclusions discussed.

Risks to the stratospheric ozone shield in the Anthropocene : This article belongs to Ambio's 50th Anniversary Collection. Theme: Ozone Layer

Crutzen (1974) and Crutzen and Ehhalt (1977) presented two key papers in Ambio that in Ambioexemplify how science first revealed to humankind the potential for damage to our ozone shield in the Anthropocene. Crutzen's (1974) review is a sweeping summary of the risks to the ozone layer from supersonic aircraft, chlorofluorocarbons, as well as nuclear weapons testing and nuclear war. Crutzen and Ehhalt (1977) described how the nitrous oxide produced from fertilizers could pose another threat to the stability of the stratospheric ozone layer. The two papers are part of a body of influential scientific work that led to the pioneering Montreal Protocol to Protect the Earth's Ozone Layer to phase out production of chlorofluorocarbons (in 1987), as well as national decisions that slowed or stopped production of supersonic planes (in the 1970s). They remain guideposts today for ongoing international negotiations regarding reducing emissions from fertilizer and limiting nuclear testing.

Nitric oxide-dependent anaerobic ammonium oxidation

Nitric oxide (NO) has important functions in biology and atmospheric chemistry as a toxin, signaling molecule, ozone depleting agent and the precursor of the greenhouse gas nitrous oxide (N₂O). Although NO is a potent oxidant, and was available on Earth earlier than oxygen, it is unclear whether NO can be used by microorganisms for growth. Anaerobic ammonium-oxidizing (anammox) bacteria couple nitrite reduction to ammonium oxidation with NO and hydrazine as intermediates, and produce N₂ and nitrate. Here, we show that the anammox bacterium Kuenenia stuttgartiensis is able to grow in the absence of nitrite by coupling ammonium oxidation to NO reduction, and produce only N₂. Under these growth conditions, the transcription of proteins necessary for NO generation is downregulated. Our work has potential implications in the control of N₂O and NO emissions from natural and manmade ecosystems, where anammox bacteria contribute significantly to N₂ release to the atmosphere. We hypothesize that microbial NO-dependent ammonium oxidation may have existed on early Earth.

100 Years of Progress in Gas-Phase Atmospheric Chemistry Research

Remarkable progress has occurred over the last 100 years in our understanding of atmospheric chemical composition, stratospheric and tropospheric chemistry, urban air pollution, acid rain, and the formation of airborne particles from gas-phase chemistry. Much of this progress was associated with the developing understanding of the formation and role of ozone and of the oxides of nitrogen, NO and NO2, in the stratosphere and troposphere. The chemistry of the stratosphere, emerging from the pioneering work of Chapman in 1931, was followed by the discovery of catalytic ozone cycles, ozone destruction by chlorofluorocarbons, and the polar ozone holes, work honored by the 1995 Nobel Prize in Chemistry awarded to Crutzen, Rowland, and Molina. Foundations for the modern understanding of tropospheric chemistry were laid in the 1950s and 1960s, stimulated by the eye-stinging smog in Los Angeles. The importance of the hydroxyl (OH) radical and its relationship to the oxides of nitrogen (NO and NO2) emerged. The chemical processes leading to acid rain were elucidated. The atmosphere contains an immense number of gas-phase organic compounds, a result of emissions from plants and animals, natural and anthropogenic combustion processes, emissions from oceans, and from the atmospheric oxidation of organics emitted into the atmosphere. Organic atmospheric particulate matter arises largely as gas-phase organic compounds undergo oxidation to yield low-volatility products that condense into the particle phase. A hundred years ago, quantitative theories of chemical reaction rates were nonexistent. Today, comprehensive computer codes are available for performing detailed calculations of chemical reaction rates and mechanisms for atmospheric reactions. Understanding the future role of atmospheric chemistry in climate change and, in turn, the impact of climate change on atmospheric chemistry, will be critical to developing effective policies to protect the planet.

Mechanism of the Chemiluminescent Reaction between Nitric Oxide and Ozone

The gas phase reaction of nitric oxide with ozone to give chemiluminescence is used extensively for detection of nitrogen oxides. The molecular mechanism of chemiluminescence in this reaction is not known. So far, the only chemiluminescent systems studied in depth are certain cycloperoxides, which emit light following decomposition. Given our understanding of the mechanism of chemiluminescence in those molecules, one would expect by extension that in the NO + O₃ reaction the chemiluminescent species (NO₂ in this case) is formed in the excited state through a reaction pathway that diverges from the ground state pathway near the transition state. A systematic search for such a pathway leads us to conclude that such a mechanism is unlikely. Instead, our study suggests that chemiluminescence in the NO + O₃ reaction is due to emission from the NO₂ vibronic states associated with the ground (X̃ ²A₁) and first excited (à ²B₂) electronic states, which are populated in the nascent NO₂ produced in the reaction. The vibronic coupling between the X̃ ²A₁ and à ²B₂ states of NO₂ is due to a conical intersection (CI), which is geometrically and energetically close to the à ²B₂ minimum energy geometry and only 1.3 eV higher than ground state NO₂. Further, the CI is 1.2 eV lower than the energy of the NO + O₃ reactants and therefore thermodynamically accessible following the reaction. An analysis of the product energy distribution indicates that the major fraction of the reaction energy is channeled into the vibrational modes of NO₂, sufficient to populate the vibronic states of NO₂ around the X̃/à CI. These vibronic states show dipole-allowed emission in a frequency range that is consistent with the observed broad chemiluminescence spectrum.

Assessment of Particle Pollution from Jetliners: from Smoke Visibility to Nanoparticle Counting

Aviation is a substantial and a fast growing emissions source. Besides greenhouse gases, aircraft engines emit black carbon (BC), a climate forcer and air pollutant. Aviation BC emissions have been regulated and estimated through exhaust smoke visibility (smoke number). Their impacts are poorly understood because emission inventories lack representative data. Here, we measured BC mass and number-based emissions of the most popular airliner's engines according to a new emission standard. We used a calibrated engine performance model to determine the emissions on the ground, at cruise altitude, and over entire flight missions. Compared to previous estimates, we found up to a factor of 4 less BC mass emitted from the standardized landing and takeoff cycle and up to a factor of 40 less during taxiing. However, the taxi phase accounted for up to 30% of the total BC number emissions. Depending on the fuel composition and flight distance, the mass and number-based emission indices (/kg fuel burned) were 6.2-14.7 mg and 2.8 × 10¹⁴ - 8.7 × 10¹⁴, respectively. The BC mass emissions per passenger-km were similar to gasoline vehicles, but the number-based emissions were relatively higher, comparable to old diesel vehicles. This study provides representative data for models and will lead to more accurate assessments of environmental impacts of aviation.

Microbial Potential for Ecosystem N Loss Is Increased by Experimental N Deposition

Fossil fuel combustion and fertilizer use has increased the amount of biologically available N entering terrestrial ecosystems. Nonetheless, our understanding of how anthropogenic N may alter the physiological mechanisms by which soil microorganisms cycle N in soil is still developing. Here, we applied shotgun metagenomics to a replicated long-term field experiment to determine how two decades of experimental N deposition, at a rate expected by mid-century, has affected the genetic potential of the soil microbial community to cycle N in soils. Experimental N deposition lead to a significant and persistent increase in functional assemblages mediating N cycle transformations associated with ecosystem N loss (i.e., denitrification and nitrification), whereas functional assemblages associated with N input and retention (i.e., N fixation and microbial N assimilation) were less positively affected. Furthermore, the abundance and composition of microbial taxa, as well as functional assemblages involved in housekeeping functions (i.e., DNA replication) were unaffected by experimental N deposition. Taken together, our results suggest that functional genes and gene pathways associated with ecosystem N loss have been favored by experimental N deposition, which may represent a genetic mechanism fostering increased N loss as anthropogenic N deposition increases in the future.

Active Adoption of Void Formation in Metal-Oxide for All Transparent Super-Performing Photodetectors

Could ‘defect-considered’ void formation in metal-oxide be actively used? Is it possible to realize stable void formation in a metal-oxide layer, beyond unexpected observations, for functional utilization? Herein we demonstrate the effective tailoring of void formation of NiO for ultra-sensitive UV photodetection. NiO was formed onto pre-sputtered ZnO for a large size and spontaneously formed abrupt p-NiO/n-ZnO heterojunction device. To form voids at an interface, rapid thermal process was performed, resulting in highly visible light transparency (85–95%). This heterojunction provides extremely low saturation current (<0.1 nA) with an extraordinary rectifying ratio value of over 3000 and works well without any additional metal electrodes. Under UV illumination, we can observe the fast photoresponse time (10 ms) along with the highest possible responsivity (1.8 A W⁻¹) and excellent detectivity (2 × 10¹³ Jones) due to the existence of an intrinsic-void layer at the interface. We consider this as the first report on metal-oxide-based void formation (Kirkendall effect) for effective photoelectric device applications. We propose that the active adoption of ‘defect-considered’ Kirkendall-voids will open up a new era for metal-oxide based photoelectric devices.

Major Issues of Air Pollution

Environmental issues change from place to place and time to time. The issues include local as well as global issues. The understanding of issues is necessary to find solution. Air pollution issues have changed over a period of time. Issues like atmospheric brown cloud, climate change, hazardous air pollutants, black/muddy snow which are hardly discussed few decades back have now gaining importance. This chapter elaborates major issues due to air pollution.

Measuring and modeling the lifetime of nitrous oxide including its variability

Nitrous oxide lifetime is computed empirically from MLS satellite dataEmpirical N2O lifetimes compared with models including interannual variabilityResults improve values for present anthropogenic and preindustrial emissions.

Beyond xeroderma pigmentosum: DNA damage and repair in an ecological context. A tribute to James E. Cleaver

The ability to repair DNA is a ubiquitous characteristic of life on Earth and all organisms possess similar mechanisms for dealing with DNA damage, an indication of a very early evolutionary origin for repair processes. James E. Cleaver's career (initiated in the early 1960s) has been devoted to the study of mammalian ultraviolet radiation (UVR) photobiology, specifically the molecular genetics of xeroderma pigmentosum and other human diseases caused by defects in DNA damage recognition and repair. This work by Jim and others has influenced the study of DNA damage and repair in a variety of taxa. Today, the field of DNA repair is enhancing our understanding of not only how to treat and prevent human disease, but is providing insights on the evolutionary history of life on Earth and how natural populations are coping with UVR-induced DNA damage from anthropogenic changes in the environment such as ozone depletion.

Aircraft engine exhaust emissions and other airport-related contributions to ambient air pollution: A review

Civil aviation is fast-growing (about +5% every year), mainly driven by the developing economies and globalisation. Its impact on the environment is heavily debated, particularly in relation to climate forcing attributed to emissions at cruising altitudes and the noise and the deterioration of air quality at ground-level due to airport operations. This latter environmental issue is of particular interest to the scientific community and policymakers, especially in relation to the breach of limit and target values for many air pollutants, mainly nitrogen oxides and particulate matter, near the busiest airports and the resulting consequences for public health. Despite the increased attention given to aircraft emissions at ground-level and air pollution in the vicinity of airports, many research gaps remain. Sources relevant to air quality include not only engine exhaust and non-exhaust emissions from aircraft, but also emissions from the units providing power to the aircraft on the ground, the traffic due to the airport ground service, maintenance work, heating facilities, fugitive vapours from refuelling operations, kitchens and restaurants for passengers and operators, intermodal transportation systems, and road traffic for transporting people and goods in and out to the airport. Many of these sources have received inadequate attention, despite their high potential for impact on air quality. This review aims to summarise the state-of-the-art research on aircraft and airport emissions and attempts to synthesise the results of studies that have addressed this issue. It also aims to describe the key characteristics of pollution, the impacts upon global and local air quality and to address the future potential of research by highlighting research needs.

Structure, stability, and properties of the trans peroxo nitrate radical: the importance of nondynamic correlation

We report a comparative single-reference and multireference coupled-cluster investigation on the structure, potential energy surface, and IR spectroscopic properties of the trans peroxo nitrate radical, one of the key intermediates in stratospheric NOX chemistry. The previous single-reference ab initio studies predicted an unbound structure for the trans peroxo nitrate radical. However, our Fock space multireference coupled-cluster calculation confirms a bound structure for the trans peroxo nitrate radical, in accordance with the experimental results reported earlier. Further, the analysis of the potential energy surface in FSMRCC method indicates a well-behaved minima, contrary to the shallow minima predicted by the single-reference coupled-cluster method. The harmonic force field analysis, of various possible isomers of peroxo nitrate also reveals that only the trans structure leads to the experimentally observed IR peak at 1840 cm(-1). The present study highlights the critical importance of nondynamic correlation in predicting the structure and properties of high-energy stratospheric NOx radicals.

A chronology of human understanding of the nitrogen cycle

Nitrogen over the ages! It was discovered in the eighteenth century. The following century, its importance in agriculture was documented and the basic components of its cycle were elucidated. In the twentieth century, a process to provide an inexhaustible supply of reactive N (Nr; all N species except N2) for agricultural, industrial and military uses was invented. This discovery and the extensive burning of fossil fuels meant that by the beginning of the twenty-first century, anthropogenic sources of newly created Nr were two to three times that of natural terrestrial sources. This caused a fundamental change in the nitrogen cycle; for the first time, there was the potential for enough food to sustain growing populations and changing dietary patterns. However, most Nr created by humans is lost to the environment, resulting in a cascade of negative earth systems impacts-including enhanced acid rain, smog, eutrophication, greenhouse effect and stratospheric ozone depletion, with associated impacts on human and ecosystem health. The impacts continue and will be magnified, as Nr is lost to the environment at an even greater rate. Thus, the challenge for the current century is how to optimize the uses of N while minimizing the negative impacts.

Stratospheric ozone, global warming, and the principle of unintended consequences--an ongoing science and policy success story

In 1974, Mario Molina and F. Sherwood Rowland warned that chlorofluorocarbons (CFCs) could destroy the stratospheric ozone layer that protects Earth from harmful ultraviolet radiation. In the decade after scientists documented the buildup and long lifetime of CFCs in the atmosphere; found the proof that CFCs chemically decomposed in the stratosphere and catalyzed the depletion of ozone; quantified the adverse effects; and motivated the public and policymakers to take action. In 1987, 24 nations plus the European Community signed the Montreal Protocol. Today, 25 years after the Montreal Protocol was agreed, every United Nations state is a party (universal ratification of 196 governments); all parties are in compliance with the stringent controls; 98% of almost 100 ozone-depleting chemicals have been phased out worldwide; and the stratospheric ozone layer is on its way to recovery by 2065. A growing coalition of nations supports using the Montreal Protocol to phase down hydrofluorocarbons, which are ozone safe but potent greenhouse gases. Without rigorous science and international consensus, emissions of CFCs and related ozone-depleting substances (ODSs) could have destroyed up to two-thirds of the ozone layer by 2065, increasing the risk of causing millions of cancer cases and the potential loss of half of global agricultural production. Furthermore, because most, ODSs are also greenhouse gases, CFCs and related ODSs could have had the effect of the equivalent of 24-76 gigatons per year of carbon dioxide. This critical review describes the history of the science of stratospheric ozone depletion, summarizes the evolution of control measures and compliance under the Montreal Protocol and national legislation, presents a review of six separate transformations over the last 100 years in refrigeration and air conditioning (A/C) technology, and illustrates government-industry cooperation in continually improving the environmental performance of motor vehicle A/C.

Stratospheric ozone depletion due to nitrous oxide: influences of other gases

The effects of anthropogenic emissions of nitrous oxide (N(2)O), carbon dioxide (CO(2)), methane (CH(4)) and the halocarbons on stratospheric ozone (O(3)) over the twentieth and twenty-first centuries are isolated using a chemical model of the stratosphere. The future evolution of ozone will depend on each of these gases, with N(2)O and CO(2) probably playing the dominant roles as halocarbons return towards pre-industrial levels. There are nonlinear interactions between these gases that preclude unambiguously separating their effect on ozone. For example, the CH(4) increase during the twentieth century reduced the ozone losses owing to halocarbon increases, and the N(2)O chemical destruction of O(3) is buffered by CO(2) thermal effects in the middle stratosphere (by approx. 20% for the IPCC A1B/WMO A1 scenario over the time period 1900-2100). Nonetheless, N(2)O is expected to continue to be the largest anthropogenic emission of an O(3)-destroying compound in the foreseeable future. Reductions in anthropogenic N(2)O emissions provide a larger opportunity for reduction in future O(3) depletion than any of the remaining uncontrolled halocarbon emissions. It is also shown that 1980 levels of O(3) were affected by halocarbons, N(2)O, CO(2) and CH(4), and thus may not be a good choice of a benchmark of O(3) recovery.