SO2 Injection Research Articles

Improved estimation of volcanic SO<sub>2</sub> injections from satellite retrievals and Lagrangian transport simulations: the 2019 Raikoke eruption

Abstract. Monitoring and modeling of volcanic plumes are important for understanding the impact of volcanic activity on climate and for practical concerns, such as aviation safety or public health. Here, we apply the Lagrangian transport model Massive-Parallel Trajectory Calculations (MPTRAC) to estimate the SO2 injections into the upper troposphere and lower stratosphere by the eruption of the Raikoke volcano (48.29∘ N, 153.25∘ E) in June 2019 and its subsequent long-range transport and dispersion. First, we used SO2 retrievals from the AIRS (Atmospheric Infrared Sounder) and TROPOMI (TROPOspheric Monitoring Instrument) satellite instruments together with a backward trajectory approach to estimate the altitude-resolved SO2 injection time series. Second, we applied a scaling factor to the initial estimate of the SO2 mass and added an exponential decay to simulate the time evolution of the total SO2 mass. By comparing the estimated SO2 mass and the mass from TROPOMI retrievals, we show that the volcano injected 2.1 ± 0.2 Tg SO2, and the e-folding lifetime of the SO2 was about 13 to 17 d. The reconstructed SO2 injection time series are consistent between using the AIRS nighttime and the TROPOMI daytime products. Further, we compared forward transport simulations that were initialized by AIRS and TROPOMI SO2 products with a constant SO2 injection rate. The results show that the modeled SO2 change, driven by chemical reactions, captures the SO2 mass variations from TROPOMI retrievals. In addition, the forward simulations reproduce the SO2 distributions in the first ∼10 d after the eruption. However, diffusion in the forward simulations is too strong to capture the internal structure of the SO2 clouds, which is further quantified in the simulation of the compact SO2 cloud from late July to early August. Our study demonstrates the potential of using combined nadir satellite retrievals and Lagrangian transport simulations to further improve SO2 time- and height-resolved injection estimates of volcanic eruptions.

An interactive stratospheric aerosol model intercomparison of solar geoengineering by stratospheric injection of SO<sub>2</sub> or accumulation-mode sulfuric acid aerosols

Abstract. Studies of stratospheric solar geoengineering have tended to focus on modification of the sulfuric acid aerosol layer, and almost all climate model experiments that mechanistically increase the sulfuric acid aerosol burden assume injection of SO2. A key finding from these model studies is that the radiative forcing would increase sublinearly with increasing SO2 injection because most of the added sulfur increases the mass of existing particles, resulting in shorter aerosol residence times and aerosols that are above the optimal size for scattering. Injection of SO3 or H2SO4 from an aircraft in stratospheric flight is expected to produce particles predominantly in the accumulation-mode size range following microphysical processing within an expanding plume, and such injection may result in a smaller average stratospheric particle size, allowing a given injection of sulfur to produce more radiative forcing. We report the first multi-model intercomparison to evaluate this approach, which we label AM-H2SO4 injection. A coordinated multi-model experiment designed to represent this SO3- or H2SO4-driven geoengineering scenario was carried out with three interactive stratospheric aerosol microphysics models: the National Center for Atmospheric Research (NCAR) Community Earth System Model (CESM2) with the Whole Atmosphere Community Climate Model (WACCM) atmospheric configuration, the Max-Planck Institute's middle atmosphere version of ECHAM5 with the HAM microphysical module (MAECHAM5-HAM) and ETH's SOlar Climate Ozone Links with AER microphysics (SOCOL-AER) coordinated as a test-bed experiment within the Geoengineering Model Intercomparison Project (GeoMIP). The intercomparison explores how the injection of new accumulation-mode particles changes the large-scale particle size distribution and thus the overall radiative and dynamical response to stratospheric sulfur injection. Each model used the same injection scenarios testing AM-H2SO4 and SO2 injections at 5 and 25 Tg(S) yr−1 to test linearity and climate response sensitivity. All three models find that AM-H2SO4 injection increases the radiative efficacy, defined as the radiative forcing per unit of sulfur injected, relative to SO2 injection. Increased radiative efficacy means that when compared to the use of SO2 to produce the same radiative forcing, AM-H2SO4 emissions would reduce side effects of sulfuric acid aerosol geoengineering that are proportional to mass burden. The model studies were carried out with two different idealized geographical distributions of injection mass representing deployment scenarios with different objectives, one designed to force mainly the midlatitudes by injecting into two grid points at 30∘ N and 30∘ S, and the other designed to maximize aerosol residence time by injecting uniformly in the region between 30∘ S and 30∘ N. Analysis of aerosol size distributions in the perturbed stratosphere of the models shows that particle sizes evolve differently in response to concentrated versus dispersed injections depending on the form of the injected sulfur (SO2 gas or AM-H2SO4 particulate) and suggests that prior model results for concentrated injection of SO2 may be strongly dependent on model resolution. Differences among models arise from differences in aerosol formulation and differences in model dynamics, factors whose interplay cannot be easily untangled by this intercomparison.

Volcanoes and Climate: Sizing up the Impact of the Recent Hunga Tonga-Hunga Ha’apai Volcanic Eruption from a Historical Perspective

An undersea volcano at Hunga Tonga-Hunga Ha’apai (HTHH) near the South Pacific island nation of Tonga, erupted violently on 15 January 2022. Potential climate impact of the HTHH volcanic eruption is of great concern to the public; here, we intend to size up the impact of the HTHH eruption from a historical perspective. The influence of historical volcanic eruptions on the global climate are firstly reviewed, which are thought to have contributed to decreased surface temperature, increased stratospheric temperature, suppressed global water cycle, weakened monsoon circulation and El Niño-like sea surface temperature. Our understanding of the impacts of past volcanic eruptions on global-scale climate provides potential implication to evaluate the impact of the HTHH eruption. Based on historical simulations, we estimate that the current HTHH eruption with an intensity of 0.4 Tg SO2 injection will decrease the global mean surface temperature by only 0.004°C in the first year after eruption, which is within the amplitude of internal variability at the interannual time scale and thus not strong enough to have significant impacts on the global climate.

Spectroscopic Characterization of HSO2• and HOSO• Intermediates Involved in SO2 Geoengineering.

Sulfur-containing radicals HSO2• and HOSO• are key intermediates involved in stratospheric sulfur geoengineering by SO2 injection. The spectroscopic characterization and photochemistry of both radicals are crucial to understanding the chemical impact of SO2 chemistry in the stratosphere. On the basis of the efficient generation of HOSO• by flash pyrolysis of gaseous sulfinic acid, CHF2S(O)OH, a strong absorption is observed at 270 nm along with a shoulder up to 350 nm for HOSO• isolated in low-temperature noble gas matrixes (Ar and Ne). These mainly arise from the excitations from the ground state (X2A) to the C2A/D2A and A2A/B2A states, respectively. Upon a 266 nm laser irradiation, the broad absorption band in the range 320-500 nm for HSO2• appears, and it corresponds to the combination of three excitations from the X2A state to the first (A2A), second (B2A), and third (C2A) excited states. Assignment of the UV-vis spectra is consistent with the photochemistry of HOSO• and HSO2• as observed by matrix-isolation IR spectroscopy and also by the agreement with high-level ab initio calculations.

Felsic volcanism as a factor driving the end-Permian mass extinction.

The Siberian Traps large igneous province (STLIP) is commonly invoked as the primary driver of global environmental changes that triggered the end-Permian mass extinction (EPME). Here, we explore the contributions of coeval felsic volcanism to end-Permian environmental changes. We report evidence of extreme Cu enrichment in the EPME interval in South China. The enrichment is associated with an increase in the light Cu isotope, melt inclusions rich in copper and sulfides, and Hg concentration spikes. The Cu and Hg elemental and isotopic signatures can be linked to S-rich vapor produced by felsic volcanism. We use these previously unknown geochemical data to estimate volcanic SO2 injections and argue that this volcanism would have produced several degrees of rapid cooling before or coincident with the more protracted global warming. Large-scale eruptions near the South China block synchronous with the EPME strengthen the case that the STLIP may not have been the sole trigger.

Changes in stratospheric aerosol extinction coefficient after the 2018 Ambae eruption as seen by OMPS-LP and MAECHAM5-HAM

Abstract. Stratospheric aerosols are an important component of the climate system. They not only change the radiative budget of the Earth but also play an essential role in ozone depletion. These impacts are particularly noticeable after volcanic eruptions when SO2 injected with the eruption reaches the stratosphere, oxidizes, and forms stratospheric aerosol. There have been several studies in which a volcanic eruption plume and the associated radiative forcing were analyzed using climate models and/or data from satellite measurements. However, few have compared vertically and temporally resolved volcanic plumes using both measured and modeled data. In this paper, we compared changes in the stratospheric aerosol loading after the 2018 Ambae eruption observed by satellite remote sensing measurements and simulated by a global aerosol model. We use vertical profiles of the aerosol extinction coefficient at 869 nm retrieved at the Institute of Environmental Physics (IUP) in Bremen from OMPS-LP (Ozone Mapping and Profiling Suite – Limb Profiler) observations. Here, we present the retrieval algorithm and a comparison of the obtained profiles with those from SAGE III/ISS (Stratospheric Aerosol and Gas Experiment III on board the International Space Station). The observed differences are within 25 % for most latitude bins, which indicates a reasonable quality of the retrieved limb aerosol extinction product. The volcanic plume evolution is investigated using both monthly mean aerosol extinction coefficients and 10 d averaged data. The measurement results were compared with the model output from MAECHAM5-HAM (ECHAM for short). In order to simulate the eruption accurately, we use SO2 injection estimates from OMPS and OMI (Ozone Monitoring Instrument) for the first phase of eruption and the TROPOspheric Monitoring Instrument (TROPOMI) for the second phase. Generally, the agreement between the vertical and geographical distribution of the aerosol extinction coefficient from OMPS-LP and ECHAM is quite remarkable, in particular, for the second phase. We attribute the good consistency between the model and the measurements to the precise estimation of injected SO2 mass and height, as well as to the nudging to ECMWF ERA5 reanalysis data. Additionally, we compared the radiative forcing (RF) caused by the increase in the aerosol loading in the stratosphere after the eruption. After accounting for the uncertainties from different RF calculation methods, the RFs from ECHAM and OMPS-LP agree quite well. We estimate the tropical (20∘ N to 20∘ S) RF from the second Ambae eruption to be about −0.13 W m−2.

Photochemistry and Non-adiabatic Photodynamics of the HOSO Radical.

Hydroxysulfinyl radical (HOSO) is important due to its involvement in climate geoengineering upon SO2 injection and generation of the highly hygroscopic H2SO4. Its photochemical behavior in the upper atmosphere is, however, uncertain. Here we present the ultraviolet-visible photochemistry and photodynamics of this species by simulating the atmospheric conditions with high-level quantum chemistry methods. Photocleavage to HO + SO arises as the major solar-induced channel, with a minor contribution of H + SO2 photoproducts. The efficient generation of SO is relevant due to its reactivity with O3 and the consequent depletion of ozone in the stratosphere.

Stratospheric aerosol layer perturbation caused by the 2019 Raikoke and Ulawun eruptions and their radiative forcing

Abstract. In June 2019 a stratospheric eruption occurred at Raikoke (48∘ N, 153∘ E). Satellite observations show the injection of ash and SO2 into the lower stratosphere and an early entrainment of the plume into a cyclone. Following the Raikoke eruption, stratospheric aerosol optical depth (sAOD) values increased in the whole Northern Hemisphere and tropics and remained enhanced for more than 1 year, with peak values at 0.040 (short-wavelength, high northern latitudes) to 0.025 (short-wavelength, Northern Hemisphere average). Discrepancies between observations and global model simulations indicate that ash may have influenced the extent and evolution of the sAOD. Top of the atmosphere radiative forcings are estimated at values between −0.3 and -0.4Wm-2 (clear-sky) and of −0.1 to -0.2Wm-2 (all-sky), comparable to what was estimated for the Sarychev eruption in 2009. Almost simultaneously two significantly smaller stratospheric eruptions occurred at Ulawun (5∘ S, 151∘ E) in June and August. Aerosol enhancements from the Ulawun eruptions mainly had an impact on the tropics and Southern Hemisphere. The Ulawun plume circled the Earth within 1 month in the tropics. Peak shorter-wavelength sAOD values at 0.01 are found in the tropics following the Ulawun eruptions and a radiative forcing not exceeding −0.15 (clear-sky) and −0.05 (all-sky). Compared to the Canadian fires (2017), Ambae eruption (2018), Ulawun (2019) and the Australian fires (2019/2020), the highest sAOD and radiative forcing values are found for the Raikoke eruption.

Assessing terrestrial biogeochemical feedbacks in a strategically geoengineered climate

Geoengineering by injecting sulfur dioxide (SO2) into the lower stratosphere has been suggested to reduce anthropogenically induced warming. While impacts of such geoengineering on climate have been investigated in recent decades, few modeling studies have considered biogeochemical feedbacks resulting from such intervention. This study comprehensively characterizes responses and feedbacks of terrestrial ecosystems, from an ensemble of coupled high-resolution Earth system model climate change simulations, under the highest standard greenhouse gas scenario with an extreme geoengineering mitigation strategy. Under this strategy, temperature increases beyond 2020 levels due to elevated anthropogenic carbon dioxide (CO2) were completely offset by the SO2 injection. Carbon cycle feedbacks can alter the trajectory of atmospheric CO2 levels by storing or releasing additional carbon on land and in the ocean, thus moderating or amplifying climate change. We assess terrestrial biogeochemical feedbacks to climate in response to geoengineering, using model output from the Stratospheric Aerosol Geoengineering Large Ensemble (GLENS) project. Results indicate terrestrial ecosystems become a stronger carbon sink globally because of lower ecosystem respiration and diminished disturbance effects under geoengineering. An additional 79 Pg C would be stored on land by the end of the twenty-first century, yielding as much as a 4% reduction in atmospheric CO2 mole fraction without marine biogeochemical feedbacks, compared to the high greenhouse gas scenario without geoengineering.

Unusual positive effect of SO2 on Mn-Ce mixed-oxide catalyst for the SCR reaction of NOx with NH3

A high-performance denitration catalyst based on Mn-Ce mixed-oxide derived from a specific Mn/Ce precursorwas fabricated by solvothermal method. It exhibited outstanding low-temperature activity, which achieved above 90% NOx conversion in the temperature of 150–310 °C. Remarkably, Mn-Ce mixed-oxide demonstrated a much better SO2 tolerance, in which the NOx conversion increased from 92.6% to 97.8% at 150 °C after introducing 200 ppm SO2. The synthesized Mn-Ce mixed-oxide has a porous structure with abundant chemisorbed oxygen spices and exposed active sites. In addition, the increased acidity and redox capacity enhanced the catalytic activity after introducing SO2. Meanwhile, the injection of SO2 separates NH3 adsorption sites from oxidation agents, inhibiting the unwanted oxidization of ammonia to nitrogen oxides. Furthermore, the reaction pathway on Mn-Ce mixed-oxide proved to be the L-H mechanism based on in situ DRIFTS. Thus, the synthesized Mn-Ce mixed oxide demonstrated an excellent denitration performance and the especially high SO2 tolerance, showing great potential for low-temperature NH3-SCR.

A specialised delivery system for stratospheric sulphate aerosols: design and operation

Temporary stratospheric aerosol injection (SAI) using sulphate compounds could help to mitigate some of the adverse and irreversible impacts of global warming. Among the risks and uncertainties of SAI, the development of a delivery system presents an appreciable technical challenge. Early studies indicate that specialised aircraft appear the most feasible (McClelan et al., Aurora Flight Sciences, 2010; Smith and Wagner, Environ Res Lett 13(12), 2018). Yet, their technical design characteristics, financial cost of deployment, and emissions have yet to be studied in detail. Therefore, these topics are examined in this two- part study. This first part outlines a set of injection scenarios and proposes a detailed, feasible aircraft design. Part 2 considers the resulting financial cost and equivalent CO2 emissions spanned by the scenarios and aircraft. Our injection scenarios comprise the direct injection of H2SO4 vapour over a range of possible dispersion rates and an SO2 injection scenario for comparison. To accommodate the extreme demands of delivering large payloads to high altitudes, a coupled optimisation procedure is used to design the system. This results in an unmanned aircraft configuration featuring a large, slender, strut-braced wing and four custom turbofan engines. The aircraft is designed to carry high-temperature H2SO4, which is evaporated prior to injection into a single outboard engine plume. Optimised flight profiles are produced for each injection scenario, all involving an initial climb to an outgoing dispersion leg at 20 km altitude, followed by a return dispersion leg at a higher altitude of 20.5 km. All the scenarios considered are found to be technologically and logistically attainable. However, the results demonstrate that achieving high engine plume dispersion rates is of principal importance for containing the scale of SAI delivery systems based on direct H2SO4 injection, and to keep these competitive with systems based on SO2 injection.

Differing responses of the quasi-biennial oscillation to artificial SO<sub>2</sub> injections in two global models

Abstract. Artificial injections of sulfur dioxide (SO2) into the stratosphere show in several model studies an impact on stratospheric dynamics. The quasi-biennial oscillation (QBO) has been shown to slow down or even vanish under higher SO2 injections in the equatorial region. But the impact is only qualitatively but not quantitatively consistent across the different studies using different numerical models. The aim of this study is to understand the reasons behind the differences in the QBO response to SO2 injections between two general circulation models, the Whole Atmosphere Community Climate Model (WACCM-110L) and MAECHAM5-HAM. We show that the response of the QBO to injections with the same SO2 injection rate is very different in the two models, but similar when a similar stratospheric heating rate is induced by SO2 injections of different amounts. The reason for the different response of the QBO corresponding to the same injection rate is very different vertical advection in the two models, even in the control simulation. The stronger vertical advection in WACCM results in a higher aerosol burden and stronger heating of the aerosols and, consequently, in a vanishing QBO at lower injection rate than in simulations with MAECHAM5-HAM. The vertical velocity increases slightly in MAECHAM5-HAM when increasing the horizontal resolution. This study highlights the crucial role of dynamical processes and helps to understand the large uncertainties in the response of different models to artificial SO2 injections in climate engineering studies.

Probabilistic hazard maps for operational use: the case of SO2 air pollution during the Holuhraun eruption (Bárðarbunga, Iceland) in 2014–2015

The Holuhraun fissure eruption (Iceland) in 2014–2015, which originated from the Barðarbunga volcanic system, was exceptional in several respects. It lasted 6 months and, throughout its duration, it released up to 9.6 Mt of SO2 in the atmosphere. The main recorded hazard affecting the entire country over the 6 months was the constant presence of a low-level gas cloud that led to recurrent air pollution episodes. The Icelandic Meteorological Office responded to this human health hazard by (1) setting up a forecasting system to anticipate the distribution of SO2 over Iceland and (2) preparing probabilistic hazard maps to support the decisions taken by the Icelandic Civil Protection in demarcating the accessible area around the eruption site. This paper introduces some technical aspects of the application of the CALPUFF numerical model to this eruption like the SO2 dispersal forecasting setup, the volcanic source numerical description, and the Monte Carlo procedure adopted for the creation of the probabilistic hazard maps. CALPUFF-based maps were created in January 2015, when the eruption was still ongoing, with the assumption that the eruption would be continuing with the same intensity. Maps for the entire country and for a smaller domain were produced, the latter showing the likelihood to exceeding an hourly concentration of 2600 μg/m3 (1 ppm) of SO2 for the spring season, a level chosen by the Icelandic Civil Protection for the delineation of the area of restricted access around the eruption site. As during the eruption there was no time for a rigorous evaluation of the model accuracy, we then undertook a retrospective analysis of CALPUFF model performance comparing the forecasted hourly SO2 concentration with real-time measurements at key-sites. The model did reproduce the hourly observations (the maximum within a 24-running window) with a level of agreement of 50.6% in Mývatn (85 km from the eruption site) and 50.4% in Reykjavik (258 km), when instances of null pairs have been removed. In Mývatn, the model overestimated the concentration more than 22% of the time. In Hofn (104 km), the model accuracy is 81.7% and occurrences of underestimation are higher than 11% of the time. In Reyðarfjorður (at 124 km), the model accuracy is assessed to be 82.7% and the model overestimates occurring 15.1% of the time. Possible explanations for the observed mismatch between model results and measurements include the spatial resolution of meteorological data field, the capability into reproducing chemical reactions of SO2 in atmosphere, and the reduced extension of the numerical domain. In addition, the model performance is strongly dependent on the source descriptors (e.g., strength of the SO2 flux and injection height) that, in this contribution, have been kept constant over long periods—neglecting, in this way, the natural variability of a dynamic emission of SO2. This consideration points toward the need of frequent and high-quality observation data for the initialization of dispersal numerical model. In light of this retrospective analysis, the probabilistic hazard maps possibly over-estimated the area exposed to high level of SO2 concentration. All the same, this paper reports on how quantitative probabilistic hazard mapping can be used for mitigating the health risk of volcanic SO2 emissions during a volcanic crisis to the benefit of operational hazard monitoring in support an effective crisis response.

A specialised delivery system for stratospheric sulphate aerosols (part 2): financial cost and equivalent CO2 emission

Temporary stratospheric aerosol injection (SAI) using sulphate compounds could help avoid some of the adverse and irreversible impacts of global warming, but comprises many risks and uncertainties. Among these, the direct financial cost and carbon emissions of potential SAI delivery systems have hitherto received only modest attention. Therefore, this paper quantifies the initial and operating financial costs and initial and operating equivalent CO2 (CO2eq) emissions of the specialised aircraft-based SAI delivery system developed with relatively high-fidelity tools in part 1 of this series. We analyse an interval of operating conditions, within which we devote special attention to four injection scenarios outlined in part 1: Three scenarios where H2SO4 vapour is directly injected at several dispersion rates and one SO2 injection scenario. We estimate financial cost through Raymer’s adjustment of Rand Corporation’s Development and Production Costs for Aircraft (DAPCA) model, augmented by additional data. CO2eq emission is computed from existing data and the computed fuel consumption for each of the scenarios. The latter estimates include an emission weighting factor to account for non-CO2 aircraft combustion products at altitude. For direct H2SO4 injection, both financial cost and CO2eq emission are sensitive to the design dispersion rate. For scenarios where higher dispersion rates are achieved, the delivery system’s cost and CO2eq are relatively small compared with the presumed benefits of SAI. The most optimistic H2SO4 scenario is found to have a financial cost and CO2eq emission similar to that of SO2 injection, while potentially allowing for reductions in the annual mass of sulphur injected to achieve a target negative radiative forcing. The estimates of financial cost and CO2eq emission were subjected to sensitivity analyses in several key parameters, including aircraft operational empty weight, engine specific fuel consumption, fuel price and aerosol price. The results indicate that the feasibility of the considered scenarios is robust.

Soil Moisture and Other Hydrological Changes in a Stratospheric Aerosol Geoengineering Large Ensemble

AbstractStratospheric sulfate aerosol geoengineering has been proposed as a potential strategy to reduce the impacts of climate change. Here we investigate the impact of stratospheric aerosol geoengineering on the terrestrial hydrological cycle. We use the Geoengineering Large Ensemble, which involves a 20‐member ensemble of simulations using the Community Earth System Model with the Whole Atmosphere Community Climate Model, in which sulfur dioxide (SO2) was injected into the stratosphere at four different locations, to maintain global mean surface temperature, and also the interhemispheric and equator‐to‐pole temperature gradients at values representative of 2020 (“baseline”) under the Representative Concentration Pathway 8.5. In our simulations, annual mean land precipitation and evapotranspiration (ET) increase by 12% each under Representative Concentration Pathway 8.5. Under the Geoengineering Large Ensemble, the hydrological cycle is suppressed compared to the baseline, with end‐of‐century decreases of 1.4% (12 ± 5 mm/year) and 3.3% (18 ± 2 mm/year) in global mean, annual mean precipitation, and ET over land, respectively. Geoengineering effectively maintains global mean soil moisture under a high CO2 scenario, although there is significant regional variability. Summertime soil moisture is reduced by 42 ± 11 kg/m2 (3.5%) and 27 ± 16 kg/m2 (2.1%) in India and the Amazon, respectively, which is dominated by the decrease in precipitation. We also compare these regional changes in soil moisture under the Geoengineering Large Ensemble with an equatorial‐only SO2 injection case and find a similar sign in residual changes, although the magnitude of the changes is larger in the equatorial run.

H2O and/or SO2 Tolerance of Cu-Mn/SAPO-34 Catalyst for NO Reduction with NH3 at Low Temperature

A series of molecular sieve catalysts (Cu–Mn/SAPO-34) with different loadings of Cu and Mn components were prepared by the impregnation method. The deNOx activity of the catalyst was investigated during the selective catalytic reduction (SCR) of NO with NH3 in the temperature range of 120 °C to 330 °C, including the effects of H2O vapors and SO2. In order to understand the poisoning mechanism by the injection of H2O and/or SO2 into the feeding gas, the characteristics of the fresh and spent catalyst were identified by means of Brunner−Emmet−Teller (BET), X-ray Diffraction (XRD), Scanning Electronic Microscopy (SEM) and Thermal Gravity- Differential Thermal Gravity (TG-DTG). The conversion of NO by the catalyst can achieve at 72% under the reaction temperature of 120 °C, while the value reached more than 90% under the temperature between 180 °C and 330 °C. The deNOx activity test shows that the H2O has a reversible negative effect on NO conversion, which is mainly due to the competitive adsorption of H2O and NH3 on Lewis acid sites. When the reaction temperature increases to 300 °C, the poisoning effect of H2O can be negligible. The poisoning effect of SO2 on deNOx activity is dependent on the reaction temperature. At low temperature, the poisoning effect of SO2 is permanent with no recovery of deNOx activity after the elimination of SO2. The formation of (NH4)2SO4, which results in the plug of active sites and a decrease of surface area, and the competitive adsorption of SO2 and NO should be responsible for the loss of deNOx activity over Cu/SAPO-34.

Exploring How Eruption Source Parameters Affect Volcanic Radiative Forcing Using Statistical Emulation

AbstractThe radiative forcing caused by a volcanic eruption is dependent on several eruption source parameters such as the mass of sulfur dioxide (SO2) emitted, the eruption column height, and the eruption latitude. General circulation models with prognostic aerosol and chemistry schemes can be used to investigate how each parameter influences the volcanic forcing. However, the range of multidimensional parameter space that can be explored is restricted because such simulations are computationally expensive. Here we use statistical emulation to explore the radiative impact of eruptions over a wide covarying range of SO2 emission magnitudes, injection heights, and eruption latitudes based on only 30 simulations. We use the emulators to build response surfaces to visualize and predict the sulfate aerosol e‐folding decay time, the stratospheric aerosol optical depth, and net radiative forcing of thousands of different eruptions. We find that the volcanic stratospheric aerosol optical depth and net radiative forcing are primarily determined by the mass of SO2 emitted, but eruption latitude is the most important parameter in determining the sulfate aerosol e‐folding decay time. The response surfaces reveal joint effects of the eruption source parameters in influencing the net radiative forcing, such as a stronger influence of injection height for tropical eruptions than high‐latitude eruptions. We also demonstrate how the emulated response surfaces can be used to find all combinations of eruption source parameters that produce a particular volcanic response, often revealing multiple solutions.

Holistic Assessment of SO2 Injections Using CESM1(WACCM): Introduction to the Special Issue

AbstractWe introduce a special issue on a holistic assessment of solar geoengineering via stratospheric SO2 injection in the state‐of‐the‐art climate model, Community Earth System Model, version 1 with the Whole Atmosphere Community Climate Model as its atmospheric component (CESM1(WACCM)). This model has numerous complexities that allow it to represent some of the most important nonlinearities associated with stratospheric SO2 injection, including aerosol microphysical growth and stratospheric chemistry. The studies described herein represent the steps toward and first attempt in a state‐of‐the‐art climate model to use solar geoengineering to meet multiple simultaneous objectives via SO2 injection at multiple locations. First, a set of simulations was carried out to better understand the response of the model to variations in latitude, altitude, and amount of sulfur dioxide injections. Subsequently, in a century‐long simulation, a feedback algorithm was employed to meet specific objectives and manage uncertainty, wherein the injection amount at each location was adjusted every model year. Most of the analyses contained in this special issue focus on surface climate and stratospheric changes in the simulations. In addition, 20 ensemble members of the feedback simulation have been carried out and provided to the community (the Geoengineering Large Ensemble) to expand the scope of analyses to low signal‐to‐noise ratio fields, including regional effects, impacts assessment, and extreme events. The demonstration provided by these simulations is a step toward understanding the space of achievable climate objectives via solar geoengineering or, phrased differently, determining what solar geoengineering can do and what it cannot do.

Sources of High Sulfate Aerosol Concentration Observed at Cape Hedo in Spring 2012

ABSTRACT Intensive observation campaigns approximately 1 week long were conducted periodically from March 2010 to November 2015 at Cape Hedo, Okinawa, Japan. The maximum daily mean sulfate aerosol (SO42–) concentrations surpassed 15 µg m–3 in spring 2012. In this study, source apportionment for these high concentrations was conducted using an air quality model with the tagged tracer method, and the main source was identified as volcanoes in March and as anthropogenic emissions from China in April. In March, the prevailing northerly wind transported a volcanic SO2 plume with a low conversion ratio to Cape Hedo. The impacts of 15 volcanoes in Japan were estimated, and a substantial impact from Sakurajima, which accounted for more SO2 than anthropogenic emissions from Japan, was found. Because the model had difficulty capturing the highest concentration, three sensitivity simulations were performed to consider the uncertainty of the volcanic SO2 emission amounts and injection heights, revealing the importance of the injection height in addition to the SO2 emission amount. Throughout April, contributions from anthropogenic emissions from China were found; hence, this source was further divided into 31 provincial scales. Shandong and Jiangsu Provinces, which are the first and seventh largest emission sources in China, respectively, were identified as significant sources at Cape Hedo. These sources showed day-to-day variation in their contributions, and the highest contribution from Shandong Province occurred on April 23, whereas that from Jiangsu Province occurred on April 22.

Response of Surface Ultraviolet and Visible Radiation to Stratospheric SO2 Injections

Climate modification by stratospheric SO2 injections, to form sulfate aerosols, may alter the spectral and angular distributions of the solar ultraviolet and visible radiation that reach the Earth’s surface, with potential consequences to environmental photobiology and photochemistry. We used modeling results from the CESM1(WACCM) stratospheric aerosol geoengineering large ensemble (GLENS) project, following the RCP8.5 emission scenario, and one geoengineering experiment with SO2 injections in the stratosphere, designed to keep surface temperatures at 2020 levels. Zonally and monthly averaged vertical profiles of O3, SO2, and sulfate aerosols, at 30 N and 70 N, served as input into a radiative transfer model, to compute biologically active irradiances for DNA damage (iDNA), UV index (UVI), photosynthetically active radiation (PAR), and two key tropospheric photodissociation coefficients (jO1D for O3 + hν (λ < 330 nm) → O(1D) + O2; and jNO2 for NO2 + hν (λ < 420 nm) → O(3P) + NO). We show that the geoengineering scenario is accompanied by substantial reductions in UV radiation. For example, comparing March 2080 to March 2020, iDNA decreased by 25% to 29% in the subtropics (30 N) and by 26% to 33% in the polar regions (70 N); UVI decreased by 19% to 20% at 30 N and 23% to 26% at 70 N; and jO1D decreased by 22% to 24% at 30 N and 35% to 40% at 70 N, with comparable contributions from sulfate scattering and stratospheric O3 recovery. Different responses were found for processes that depend on longer UV and visible wavelengths, as these are minimally affected by ozone; PAR and jNO2 were only slightly lower (9–12%) at 30 N, but much lower at 70 N (35–40%). Similar reductions were estimated for other months (June, September, and December). Large increases in the PAR diffuse-direct ratio occurred in agreement with previous studies. Absorption by SO2 gas had a small (~1%) effect on jO1D, iDNA, and UVI, and no effect on jNO2 and PAR.