Short-term variations in the oxidizing power of the atmosphere

Reduced greenhouse gas emission by reactive oxygen species during composting

Reactive oxygen species (ROS) is produced in the composting, which effectively promote organic matter transformation and humification process, but the effect of ROS on greenhouse gas emissions in this process has not been understood. This study proposed and validated that ROS can effectively reduce greenhouse gas emissions intheprocessofcomposting. Compared with ordinary thermophilic composting (oTC), thermophilic composting (imTC) that was supplemented by iron mineral increased ROS production by 1.38 times, and significantly reduced greenhouse gas emissions by 45.12%. Microbial community analysis showed no significant difference in the abundance of microbes involved in greenhouse gas production between oTC and imTC. Further correlation analysis proved that ROS played a crucial role in influencing greenhouse gas emissions throughout the composting process, especially in the initial phase. These findings provide new strategies for managing livestock and poultry manure to mitigate climate change.

Interannual changes in atmospheric oxidation over forests determined from space

The hydroxyl radical (OH) is the central oxidant in Earth's troposphere, but its temporal variability is poorly understood. We combine 2012-2020 satellite-based isoprene and formaldehyde measurements to identify coherent OH changes over temperate and tropical forests with attribution to emission trends, biotic stressors, and climate. We identify a multiyear OH decrease over the Southeast United States and show that with increasingly hot/dry summers the regional chemistry could become even less oxidizing depending on competing temperature/drought impacts on isoprene. Furthermore, while global mean OH decreases during El Niño, we show that near-field effects over tropical rainforests can alternate between high/low OH anomalies due to opposing fire and biogenic emission impacts. Results provide insights into how atmospheric oxidation will evolve with changing emissions and climate.

Dependence of Biotic and Abiotic H2O2 and •OH Production on the Redox Conditions and Compositions of Sediment during Oxygenation

Reactive oxygen species (ROS) production in O2-perturbed subsurface environments has been increasingly documented in recent years. However, the constraining conditions under which abiotic and/or biotic mechanisms predominate for ROS production remain ambiguous. Here, we demonstrate that the ROS production mechanism, biotic and abiotic, is determined by sediment redox properties and sediment compositions. Upon the oxygenation of 10 field sediments, the cumulative H2O2 concentrations reached up to 554 μmol/kg within 2 h. The autoclaving sterilization experiments showed that H2O2 could be produced by both biotic and abiotic processes depending on the redox conditions. However, only the abiotic process could produce significant levels of •OH, and the production yield was closely related to the sediment components, particularly sediment Fe(II) and organic matter. Fe(II) bound with organic matter led to high yields of H2O2 and •OH production. Sediment oxygenation contributed to the appearance of H2O2 in groundwater, with the abiotic mechanism producing higher instantaneous H2O2 concentrations than the biotic mechanism. These findings reveal that the redox conditions, compositions, and texture of sediments collectively control abiotic and biotic mechanisms for ROS production, which assists the identification of ROS production hotspots and the understanding of ROS distribution and utilization in the subsurface.

In Situ Visualization on Surface Oxidative Corrosion with Free Radicals: Black Phosphorus Nanoflake as an Example

Free radicals exert a significant impact on the fate of redox-active substances and play a crucial role in the surface corrosion of solid in environment. Dynamic visualization on the response of the surface to the free radicals at nanoscale is essential to explore the mechanism. Environmental transmission electron microscopy will be a powerful tool for dynamic changes of the interface redox process of solid surface with electron beams induced free radicals, to simulate the redox process of a solid in the environment. Black phosphorus (BP), an environment-sensitive material, is selected as an example to visualize the degradation pathways with environmental transmission electron microscopy. The distribution of the corrosion initiation points, formation and growth of corrosion areas, and the eventual splintering and disappearance of BP nanoflakes are recorded vividly. In situ results are substantiated by the ex situ experiments and density functional theory (DFT) calculations. Results show that degradation originates at the edges and defect structures when the humidity reaches high enough. The microscopic structural oxidative etching of solid surface with radicals in natural light is simulated with radicals produced by electron beam irradiation on suspending medium O₂ and H₂O for the first time. This method will offer unprecedented details and valuable insights into the mechanism involved in the oxidative etching with natural light.

Environmental sustainability in anaesthesia and critical care

The detrimental health effects of climate change continue to increase. Although health systems respond to this disease burden, healthcare itself pollutes the atmosphere, land, and waterways. We surveyed the 'state of the art' environmental sustainability research in anaesthesia and critical care, addressing why it matters, what is known, and ideas for future work. Focus is placed upon the atmospheric chemistry of the anaesthetic gases, recent work clarifying their relative global warming potentials, and progress in waste anaesthetic gas treatment. Life cycle assessment (LCA; i.e. 'cradle to grave' analysis) is introduced as the definitive method used to compare and contrast ecological footprints of products, processes, and systems. The number of LCAs within medicine has gone from rare to an established body of knowledge in the past decade that can inform doctors of the relative ecological merits of different techniques. LCAs with practical outcomes are explored, such as the carbon footprint of reusable vs single-use anaesthetic devices (e.g. drug trays, laryngoscope blades, and handles), and the carbon footprint of treating an ICU patient with septic shock. Avoid, reduce, reuse, recycle, and reprocess are then explored. Moving beyond routine clinical care, the vital influences that the source of energy (renewables vs fossil fuels) and energy efficiency have in healthcare's ecological footprint are highlighted. Discussion of the integral roles of research translation, education, and advocacy in driving the perioperative and critical care environmental sustainability agenda completes this review.

Old carbon reservoirs were not important in the deglacial methane budget

Permafrost and methane hydrates are large, climate-sensitive old carbon reservoirs that have the potential to emit large quantities of methane, a potent greenhouse gas, as the Earth continues to warm. We present ice core isotopic measurements of methane (Δ¹⁴C, δ¹³C, and δD) from the last deglaciation, which is a partial analog for modern warming. Our results show that methane emissions from old carbon reservoirs in response to deglacial warming were small (<19 teragrams of methane per year, 95% confidence interval) and argue against similar methane emissions in response to future warming. Our results also indicate that methane emissions from biomass burning in the pre-Industrial Holocene were 22 to 56 teragrams of methane per year (95% confidence interval), which is comparable to today.

Water Table Fluctuations Regulate Hydrogen Peroxide Production and Distribution in Unconfined Aquifers

Significance of reactive oxygen species (ROS) in subsurface has been increasingly documented in recent years, whereas the mechanisms controlling ROS production and distribution in subsurface remain poorly understood. Here we show that water table fluctuations regulate the dynamics of hydrogen peroxide (H₂O₂) production and distribution in unconfined aquifers. In one hydrological year, we measured the dynamics of H₂O₂ distribution in an unconfined aquifer impacted by a 14 m water level fluctuation in the adjacent Yangtze River. H₂O₂ concentrations in groundwater attained up to 123 nM at rising water table stage in summer, but were low or even below the detection limit at the other stages of stable and falling water table. Lab experiments and kinetic models revealed that abiotic reactions between dissolved O₂ and reduced species (i.e., Fe(II) and organic matter) were responsible for H₂O₂ production in the aquifers. Both field observations and reactive transport models unveiled that a rising water table developed a thermodynamically unstable banded zone in the unconfined aquifer in which elevated coexisting dissolved O₂ and reduced species favored abiotic H₂O₂ production. Our findings provide fundamentals for understanding and predicting ROS distribution in unconfined aquifers, and constrain the significance of ROS in aquifers to specific temporal and spatial domains.

Sulfide drives hydroxyl radicals production in oxic ferric oxyhydroxides environments

Perturbation of Fe(III)-bearing oxic environments by reduced species such as sulfide occurs widely in natural and engineered systems. However, whether hydroxyl radicals (OH) can be produced in these environments remains unexplored. Here we show that sulfide drives OH production in Fe(III) oxyhydroxides suspensions under neutral and oxic conditions. For lepidocrocite, ferrihydrite and goethite suspensions at 11.2 mM Fe, the addition of 0.5 mM sulfide produced 14.2, 14.3 and 22.4 μM OH within 120 min, respectively. With addition of sulfide to lepidocrocite suspensions at 11.2 mM Fe, the cumulative OH concentration within 120 min increased from 0 to 14.2, 25.2, 52.6 and 63.1 μM when sulfide dosage increased from 0 to 0.5, 2.5, 5 and 7.5 mM, respectively. At a fixed sulfide dosage of 5 mM, the cumulative OH concentration increased with increasing the number of sulfide additions. The mechanisms of OH production were attributed to the generation of surface-bound Fe(II), most likely in the form of >Fe^IIOH₂⁺, and Fe(II) in the solid phase or FeS from the reactions between sulfide and Fe(III), followed by O₂ activation. OH production could take place until depletion of sulfide. Finally, we found that the generated OH could oxidize the coexisting redox-active substances like phenol under neutral and oxic conditions. Our findings reveal that sulfide perturbation of Fe(III)-bearing oxic environments is a new source of OH, and contaminants oxidation by OH necessitates consideration in these environments.

Production of Abundant Hydroxyl Radicals from Oxygenation of Subsurface Sediments

Hydroxyl radicals (•OH) play a crucial role in the fate of redox-active substances in the environment. Studies of the •OH production in nature has been constrained to surface environments exposed to light irradiation, but is overlooked in the subsurface under dark. Results of this study demonstrate that abundant •OH is produced when subsurface sediments are oxygenated under fluctuating redox conditions at neutral pH values. The cumulative concentrations of •OH produced within 24 h upon oxygenation of 33 sediments sampled from different redox conditions are 2-670 μmol •OH per kg dry sediment or 6.7-2521 μM •OH in sediment pore water. Fe(II)-containing minerals, particularly phyllosilicates, are the predominant contributor to •OH production. This production could be sustainable when sediment Fe(II) is regenerated by the biological reduction of Fe(III) during redox cycles. Production of •OH is further evident in a field injection-extraction test through injecting oxygenated water into a 23-m depth aquifer. The •OH produced can oxidize pollutants such as arsenic and tetracycline and contribute to CO2 emissions at levels that are comparable with soil respiration. These findings indicate that oxygenation of subsurface sediments is an important source of •OH in nature that has not been previously identified, and •OH-mediated oxidation represents an overlooked process for substance transformations at the oxic/anoxic interface.

Long term trends of methane, non methane hydrocarbons, and carbon monoxide in urban atmosphere

The concentrations of methane (CH4), non-methane hydrocarbons (NMHC), and carbon monoxide (CO) were measured at two urban locations (Guro (GR) and Nowon (NW)) in Seoul, Korea between 2004 and 2013. The mean amount fractions of CH4, NMHC, and CO, measured at GR over this period were 2.06±0.02, 0.32±0.03, and 0.61±0.05 ppm, respectively, while at NW they were 2.08±0.06, 0.33±0.05, and 0.54±0.06 ppm, respectively. The ratio of CH4 to the total hydrocarbon amount fraction remained constant across the study years: 0.82 to 0.90 at GR and 0.81 to 0.89 at NW. Similarly, stable ratios were also observed between NMHC and THC at the two sites. In contrast, the annual mean ratios for CH4/NMHC showed a larger variation: between 4.55 to 8.67 at GR and 4.25 to 8.45 at NW. The seasonality of CO was characterized by wintertime maxima, while for CH4 and NMHC the highest amount fractions were found in fall. The analysis of their long-term trends based on Mann-Kendall and Sen's methods showed an overall increase of THC and CH4, whereas a decreasing trend was observed for NMHC and CO.

Nanoparticles in the environment: assessment using the causal diagram approach

Nanoparticles (NPs) cause concern for health and safety as their impact on the environment and humans is not known. Relatively few studies have investigated the toxicological and environmental effects of exposure to naturally occurring NPs (NNPs) and man-made or engineered NPs (ENPs) that are known to have a wide variety of effects once taken up into an organism. A review of recent knowledge (between 2000-2010) on NP sources, and their behaviour, exposure and effects on the environment and humans was performed. An integrated approach was used to comprise available scientific information within an interdisciplinary logical framework, to identify knowledge gaps and to describe environment and health linkages for NNPs and ENPs. The causal diagram has been developed as a method to handle the complexity of issues on NP safety, from their exposure to the effects on the environment and health. It gives an overview of available scientific information starting with common sources of NPs and their interactions with various environmental processes that may pose threats to both human health and the environment. Effects of NNPs on dust cloud formation and decrease in sunlight intensity were found to be important environmental changes with direct and indirect implication in various human health problems. NNPs and ENPs exposure and their accumulation in biological matrices such as microbiota, plants and humans may result in various adverse effects. The impact of some NPs on human health by ROS generation was found to be one of the major causes to develop various diseases. A proposed cause-effects diagram for NPs is designed considering both NNPs and ENPs. It represents a valuable information package and user-friendly tool for various stakeholders including students, researchers and policy makers, to better understand and communicate on issues related to NPs.

Atmospheric photosensitized heterogeneous and multiphase reactions: from outdoors to indoors

This proposal involves direct photolysis processes occurring in the troposphere incorporating photochemical excitation and intermolecular energy transfer. The study of such processes could provide a better understanding of ·OH radical formation pathways in the atmosphere and in consequence, of a more accurate prediction of the oxidative capacity of the atmosphere. Compounds that readily absorb in the tropospheric actinic window (ionic organic complexes, PAHs, aromatic carbonyl compounds) acting as potential photosensitizers of atmospheric relevant processes are explored. The impact of hotosensitation on relevant systems which could act as powerful atmospheric reactors,that is, interface ocean-atmosphere, urban and forest surfaces and indoor air environments is also discussed.

Broader perspectives for comparing different greenhouse gases

Over the last 20 years, different greenhouse gases have been compared, in the context of climate change, primarily through the concept of global warming potentials (GWPs). This considers the climate forcing caused by pulse emissions and integrated over a fixed time horizon. Recent studies have shown that uncertainties in GWP values are significantly larger than previously thought and, while past literature in this area has raised alternative means of comparison, there is not yet any clear alternative. We propose that a broader framework for comparing greenhouse gases has become necessary and that this cannot be addressed by using simple fixed exchange rates. From a policy perspective, the framework needs to be clearly aligned with the goal of climate stabilization, and we show that comparisons between gases can be better addressed in this context by the forcing equivalence index (FEI). From a science perspective, a framework for comparing greenhouse gases should also consider the full range of processes that affect atmospheric composition and how these may alter for climate stabilization at different levels. We cover a basis for a broader approach to comparing greenhouse gases by summarizing the uncertainties in GWPs, linking those to uncertainties in the FEIs consistent with stabilization, and then to a framework for addressing uncertainties in the corresponding biogeochemical processes.

Livestock methane emission and its perspective in the global methane cycle

Over the past three centuries, the atmospheric methane burden has grown 2.5-fold, reaching levels unprecedented in at least 650 000 years. Agricultural expansion has played a large part in this anthropogenic signal, with enterically fermented methane emitted by farmed ruminant livestock accounting for about one quarter of all anthropogenic emissions. This paper summarises the range of measurements that give confidence in estimates of the emission per animal and per unit feed intake and in their extrapolation to national and global emission inventories, while noting also some of the inherent uncertainties. Global emissions are discussed in the context of the evolving global methane cycle.

Changes in tropospheric composition and air quality due to stratospheric ozone depletion and climate change

It is well-understood that reductions in air quality play a significant role in both environmental and human health. Interactions between ozone depletion and global climate change will significantly alter atmospheric chemistry which, in turn, will cause changes in concentrations of natural and human-made gases and aerosols. Models predict that tropospheric ozone near the surface will increase globally by up to 10 to 30 ppbv (33 to 100% increase) during the period 2000 to 2100. With the increase in the amount of the stratospheric ozone, increased transport from the stratosphere to the troposphere will result in different responses in polluted and unpolluted areas. In contrast, global changes in tropospheric hydroxyl radical (OH) are not predicted to be large, except where influenced by the presence of oxidizable organic matter, such as from large-scale forest fires. Recent measurements in a relatively clean location over 5 years showed that OH concentrations can be predicted by the intensity of solar ultraviolet radiation. If this relationship is confirmed by further observations, this approach could be used to simplify assessments of air quality. Analysis of surface-level ozone observations in Antarctica suggests that there has been a significant change in the chemistry of the boundary layer of the atmosphere in this region as a result of stratospheric ozone depletion. The oxidation potential of the Antarctic boundary layer is estimated to be greater now than before the development of the ozone hole. Recent modeling studies have suggested that iodine and iodine-containing substances from natural sources, such as the ocean, may increase stratospheric ozone depletion significantly in polar regions during spring. Given the uncertainty of the fate of iodine in the stratosphere, the results may also be relevant for stratospheric ozone depletion and measurements of the influence of these substances on ozone depletion should be considered in the future. In agreement with known usage and atmospheric loss processes, tropospheric concentrations of HFC-134a, the main human-made source of trifluoroacetic acid (TFA), is increasing rapidly. As HFC-134a is a potent greenhouse gas, this increasing concentration has implications for climate change. However, the risks to humans and the environment from substances, such as TFA, produced by atmospheric degradation of hydrochlorofluorocarbons (HCFCs) and hydrofluorocarbons (HFCs) are considered minimal. Perfluoropolyethers, commonly used as industrial heat transfer fluids and proposed as chlorohydrofluorocarbon (CHFC) substitutes, show great stability to chemical degradation in the atmosphere. These substances have been suggested as substitutes for CHFCs but, as they are very persistent in the atmosphere, they may be important contributors to global warming. It is not known whether these substances will contribute significantly to global warming and its interaction with ozone depletion but they should be considered for further evaluation.

Contribution of anthropogenic and natural sources to atmospheric methane variability

Methane is an important greenhouse gas, and its atmospheric concentration has nearly tripled since pre-industrial times. The growth rate of atmospheric methane is determined by the balance between surface emissions and photochemical destruction by the hydroxyl radical, the major atmospheric oxidant. Remarkably, this growth rate has decreased markedly since the early 1990s, and the level of methane has remained relatively constant since 1999, leading to a downward revision of its projected influence on global temperatures. Large fluctuations in the growth rate of atmospheric methane are also observed from one year to the next, but their causes remain uncertain. Here we quantify the processes that controlled variations in methane emissions between 1984 and 2003 using an inversion model of atmospheric transport and chemistry. Our results indicate that wetland emissions dominated the inter-annual variability of methane sources, whereas fire emissions played a smaller role, except during the 1997-1998 El Niño event. These top-down estimates of changes in wetland and fire emissions are in good agreement with independent estimates based on remote sensing information and biogeochemical models. On longer timescales, our results show that the decrease in atmospheric methane growth during the 1990s was caused by a decline in anthropogenic emissions. Since 1999, however, they indicate that anthropogenic emissions of methane have risen again. The effect of this increase on the growth rate of atmospheric methane has been masked by a coincident decrease in wetland emissions, but atmospheric methane levels may increase in the near future if wetland emissions return to their mean 1990s levels.

A comment on scaling methane emissions from vegetation and grazing ruminants in New Zealand

Keppler et al. (2006, Nature 439, 187-191) showed that plants produce methane (CH₄) in aerobic environments, leading Lowe (2006, Nature 439, 148-149) to postulate that in countries such as New Zealand, where grazed pastures have replaced forests, the forests could have produced as much CH₄ as the ruminants currently grazing these areas. Estimating CH₄ emissions from up to 85 million ruminants in New Zealand is challenging and, for completeness, the capacity of forest and pastoral soils to oxidise CH₄ should be included. On average, the CH₄ emission rate of grazing ruminants is estimated to be 9.6 ± 2.6 g m^-2 year^-1 (±standard deviation), six times the corresponding estimate for an indigenous forest canopy (1.6 ± 1.1 g m^-2 year^-1). The forest's soil is estimated to oxidise 0.9 ± 0.2 g m^-2 year^-1 more CH₄ than representative soils beneath grazed pasture. Taking into account plant and animal sources and the soil's oxidative capacity, the net CH₄ emission rates of forest and grazed ecosystems are 0.6 ± 1.1 and 9.8 ± 2.6 g m^-2 year^-1, respectively.

Strong correlation between levels of tropospheric hydroxyl radicals and solar ultraviolet radiation

The most important chemical cleaning agent of the atmosphere is the hydroxyl radical, OH. It determines the oxidizing power of the atmosphere, and thereby controls the removal of nearly all gaseous atmospheric pollutants. The atmospheric supply of OH is limited, however, and could be overcome by consumption due to increasing pollution and climate change, with detrimental feedback effects. To date, the high variability of OH concentrations has prevented the use of local observations to monitor possible trends in the concentration of this species. Here we present and analyse long-term measurements of atmospheric OH concentrations, which were taken between 1999 and 2003 at the Meteorological Observatory Hohenpeissenberg in southern Germany. We find that the concentration of OH can be described by a surprisingly linear dependence on solar ultraviolet radiation throughout the measurement period, despite the fact that OH concentrations are influenced by thousands of reactants. A detailed numerical model of atmospheric reactions and measured trace gas concentrations indicates that the observed correlation results from compensations between individual processes affecting OH, but that a full understanding of these interactions may not be possible on the basis of our current knowledge of atmospheric chemistry. As a consequence of the stable relationship between OH concentrations and ultraviolet radiation that we observe, we infer that there is no long-term trend in the level of OH in the Hohenpeissenberg data set.