Sulfate Surface Concentrations Research Articles

Sulfate diffusion in coal pillar: experimental data and prediction model

The stability of coal pillar dams is crucial for the long-term service of underground reservoirs storing water or heat. Chemical damage of coal dams induced by ions-attacking in coal is one of the main reasons for the premature failure of coal dams. However, the diffusion process of harmful ions in coal is far from clear, limiting the reliability and durability of coal dam designs. This paper investigates sulfate diffusion in coal pillar through experimental and analytical methods. Coal specimens are prepared and exposed to sulfate solutions with different concentrations. The sulfate concentrations at different locations and time are measured. Based on experimental data and Fick’s law, the time-dependent surface concentration of sulfate and diffusion coefficient are determined and formulated. Further, an analytical model for predicting sulfate diffusion in coal pillar is developed by considering dual time-dependent characteristics and Laplace transformations. Through comparisons with experimental data, the accuracy of the analytical model for predicting sulfate diffusion is verified. Further, sulfate diffusions in coal dams for different concentrations of sulfate in mine water are investigated. It has been found that the sulfate concentration of exposure surface and diffusion coefficient in coal are both time-dependent and increase with time. Conventional Fick’s law is not able to predict the sulfate diffusion in coal pillar due to the dual time-dependent characteristics. The sulfate attacking makes the coal dam a typical heterogeneous gradient structure. For sulfate concentrations 0.01–0.20 mol/L in mine water, it takes almost 1.5 and 4 years for sulfate ions to diffuse 9.46 and 18.92 m, respectively. The experimental data and developed model provide a practical method for predicting sulfate diffusion in coal pillar, which helps the service life design of coal dams.

Description and evaluation of the tropospheric aerosol scheme in the Integrated Forecasting System (IFS-AER, cycle 47R1) of ECMWF

Abstract. This article describes the Integrated Forecasting System aerosol scheme (IFS-AER) used operationally in the IFS cycle 47R1, which was operated by the European Centre for Medium Range Weather Forecasts (ECMWF) in the framework of the Copernicus Atmospheric Monitoring Services (CAMS). It represents an update of the Rémy et al. (2019) article, which described cycle 45R1 of IFS-AER in detail. Here, we detail only the parameterisations of sources and sinks that have been updated since cycle 45R1, as well as recent changes in the configuration used operationally within CAMS. Compared to cycle 45R1, a greater integration of aerosol and chemistry has been achieved. Primary aerosol sources have been updated, with the implementation of new dust and sea salt aerosol emission schemes. New dry and wet deposition parameterisations have also been implemented. Sulfate production rates are now provided by the global chemistry component of IFS. This paper aims to describe most of the updates that have been implemented since cycle 45R1, not just the ones that are used operationally in cycle 47R1; components that are not used operationally will be clearly flagged. Cycle 47R1 of IFS-AER has been evaluated against a wide range of surface and total column observations. The final simulated products, such as particulate matter (PM) and aerosol optical depth (AOD), generally show a significant improvement in skill scores compared to results obtained with cycle 45R1. Similarly, the simulated surface concentration of sulfate, organic matter and sea salt aerosol are improved by cycle 47R1 compared to cycle 45R1. Some biases persist, such as the surface concentrations of nitrate and organic matter being simulated too high. The new wet and dry deposition schemes that have been implemented into cycle 47R1 have a mostly positive impact on simulated AOD, PM and speciated aerosol surface concentration.

Comparison and evaluation of the simulated annual aerosol characteristics over China with two global aerosol models

In this study, simulations of the annual mean aerosol budget, aerosol optical properties, and surface mass concentration in 2006 in China are performed with two aerosol interactive global atmosphere models, namely, the Nonhydrostatic ICosahedral Atmospheric Model (NICAM) coupled with the Spectral Radiation Transport Model for Aerosol Species (SPRINTARS) and the Beijing Climate Center Atmospheric General Circulation Model (BCC_AGCM) coupled with the Canadian Aerosol Module (CAM) online. The observed and simulated aerosol optical depths (AODs) exhibit similar horizontal distributions with large values over eastern and central China, and sulfate aerosols contribute the main differences between the AODs simulated by NICAM and BCC_AGCM. The simulated sulfate and dust surface concentrations are more consistent with observations compared with the simulated carbonaceous surface concentrations, and both models can reproduce the decreasing tendency of the sulfate surface concentration from urban sites to rural sites. However, the dust emission and deposition levels in China simulated by BCC_AGCM are three times as high as those simulated by NICAM, and the major sink processes of the anthropogenic sulfate, black carbon (BC), and organic carbon (OC) aerosols over China are very different between the two models. The emission and deposition results, which are closely related to the model-assumed aerosol particle size distribution, indicate that the current aerosol size distribution used in the two models should be further improved. The differences in dust emission parameterizations also lead significant discrepancies in aerosol cycles and the dust emission scheme is an important factor determining the magnitudes of global and regional dust emission fluxes.

Spatiotemporal distribution of anthropogenic aerosols in China around 2030

In the context of global warming, the future spatiotemporal distribution of aerosols in China is a common concern of the government and the scientific community. In this study, the regional climate model RegCM4 is used to simulate the spatiotemporal distribution of anthropogenic aerosols including sulfate, black carbon, and organic carbon in China around 2030 under the RCP4.5 and RCP8.5 scenarios and estimate the contributions of climate difference, emission difference, and extra-regional transport difference to the change of anthropogenic aerosol concentration in the study area. The results show that the annual average concentrations of anthropogenic aerosols around 2030 decreased significantly with respect to those around 2010, and the decrease amplitude of black carbon surface concentration is the smallest, especially in the RCP8.5 scenario. The annual averages for sulfate, black carbon, and organic carbon surface concentrations in the central and eastern parts of China will be 8.5, 1.7, and 3.7 μg m−3, respectively, under the RCP4.5 scenario, whereas 10.0, 2.2, and 4.4 μg m−3, respectively, under the RCP8.5 scenario. The surface concentration of sulfate is higher in summer and spring, while lower in winter and autumn. The surface concentrations of black carbon and organic carbon are higher in winter and lower in other seasons. The results of sensitivity experiments demonstrate that the future difference in local emissions between RCP8.5 and RCP4.5 scenarios has the greatest impact on the anthropogenic aerosol concentrations throughout China, while the effects of future climate difference and extra-regional transport difference are much smaller around 2030. For the aerosol column burdens, the effect of future local emission difference between the two scenarios is still dominant, and the effect of extra-regional transport difference becomes very significant during spring and winter for organic carbon and black carbon. The results of this paper suggest that the impacts of future climate difference and extra-regional transport difference between RCP8.5 and RCP4.5 scenarios on anthropogenic aerosols are non-negligible in certain regions and seasons besides the impact of future local emission difference in China around 2030.

Re-analysis of tropospheric sulfate aerosol and ozone for the period 1980–2005 using the aerosol-chemistry-climate model ECHAM5-HAMMOZ

Abstract. Understanding historical trends of trace gas and aerosol distributions in the troposphere is essential to evaluate the efficiency of existing strategies to reduce air pollution and to design more efficient future air quality and climate policies. We performed coupled photochemistry and aerosol microphysics simulations for the period 1980–2005 using the aerosol-chemistry-climate model ECHAM5-HAMMOZ, to assess our understanding of long-term changes and inter-annual variability of the chemical composition of the troposphere, and in particular of ozone and sulfate concentrations, for which long-term surface observations are available. In order to separate the impact of the anthropogenic emissions and natural variability on atmospheric chemistry, we compare two model experiments, driven by the same ECMWF re-analysis data, but with varying and constant anthropogenic emissions, respectively. Our model analysis indicates an increase of ca. 1 ppbv (0.055 ± 0.002 ppbv yr−1) in global average surface O3 concentrations due to anthropogenic emissions, but this trend is largely masked by the larger O3 anomalies due to the variability of meteorology and natural emissions. The changes in meteorology (not including stratospheric variations) and natural emissions account for the 75 % of the total variability of global average surface O3 concentrations. Regionally, annual mean surface O3 concentrations increased by 1.3 and 1.6 ppbv over Europe and North America, respectively, despite the large anthropogenic emission reductions between 1980 and 2005. A comparison of winter and summer O3 trends with measurements shows a qualitative agreement, except in North America, where our model erroneously computed a positive trend. Simulated O3 increases of more than 4 ppbv in East Asia and 5 ppbv in South Asia can not be corroborated with long-term observations. Global average sulfate surface concentrations are largely controlled by anthropogenic emissions. Globally natural emissions are an important driver determining AOD variations. Regionally, AOD decreased by 28 % over Europe, while it increased by 19 % and 26 % in East and South Asia. The global radiative perturbation calculated in our model for the period 1980–2005 was rather small (0.05 W m−2 for O3 and 0.02 W m−2 for total aerosol direct effect), but larger perturbations ranging from −0.54 to 1.26 W m−2 are estimated in those regions where anthropogenic emissions largely varied.

Impact of ship emissions on the Mediterranean summertime pollution and climate: A regional model study

Ship emissions contribute substantially to atmospheric pollution over the summertime Mediterranean region, thereby modifying the radiation budget through sulfate aerosol forcing. By applying a regional atmospheric-chemistry model and a radiation model we determine the seasonal variability of secondary trace gases and aerosols, their origin and impact on climate. Summer mean sulfate aerosol column burden over the Mediterranean is 7.8 mg m−2 and remarkably higher than the European mean of 4.7 mg m−2. Partitioning SOx emissions into land and water sources allows to investigate their respective impact on the sulfate aerosol concentration, its total burden and direct radiative forcing. 54% of the total sulfate aerosol column burden over the Mediterranean in summer originates from ship emissions. Accordingly, they contribute over 50% to the direct radiative forcing. Running the model without ship emissions significantly reduces near surface concentration of sulfate, ozone, nitric acid, hydroxy radicals and formaldehyde. As the applied ship emission inventory is based on the year 1990 and model results tend to underestimate observed concentrations at Mediterranean locations influenced by ship emissions, we assume that increased ship emissions during the past decade contribute nowadays even stronger to secondary pollution formation and radiative forcing.

Clouds and sulfate are anticorrelated: A new diagnostic for global sulfur models

We consider the correlation between clouds and sulfate in order to assess the relative importance of cloud aqueous‐phase production of sulfate, precipatation scavenging of sulfate, and inhibition of gas‐phase sulfate production beneath clouds. Statistical analysis of observed daily cloud cover and sulfate surface concentrations in Europe and North America indicates a significant negative correlation between clouds and sulfate. This implies that clouds remove sulfate via precipitation scavenging and/or inhibit sulfate gas‐phase production more than they enhance sulfate concentration through aqueous‐phase production. Persistent sulfate/cloud anticorrelations at long timescales (8–64 days) apparently result from large‐scale dynamical influences on clouds, which in turn impact sulfate. A statistical analysis of output from the general circulation model (GCM) of the Goddard Institute for Space Studies (GISS) shows weak coherence between sulfate and cloud cover. However, there is stronger anticorrelation between the model's sulfate generated by gas‐phase oxidation and cloud cover. Sulfate/cloud anticorrelation in the GCM strengthens if we extinguish gas‐phase sulfate production beneath clouds, as should happen since the oxidant OH is photochemically generated. However the only way to achieve strong anticorrelation between total sulfate and clouds is by correcting our treatment of aqueous‐phase sulfate production. Our model, like many other global tracer models, released dissolved species (including sulfate) from clouds after each cloud time step rather than making release contingent upon cloud evaporation. After correcting this in the GISS model, more sulfate is rained out, the sulfate burden produced via the aqueous phase decreases to half its former amount, and the total sulfate burden is 25% lower.

Vertical distributions of sulfur species simulated by large scale atmospheric models in COSAM: Comparison with observations

A comparison of large-scale models simulating atmospheric sulfate aerosols (COSAM) was conducted to increase our understanding of global distributions of sulfate aerosols and precursors. Earlier model comparisons focused on wet deposition measurements and sulfate aerosol concentrations in source regions at the surface. They found that different models simulated the observed sulfate surface concentrations mostly within a factor of two, but that the simulated column burdens and vertical profiles were very different amongst different models. In the COSAM exercise, one aspect is the comparison of sulfate aerosol and precursor gases above the surface. Vertical profiles of SO2, SO2−4, oxidants and cloud properties were measured by aircraft during the North Atlantic Regional Experiment (NARE) experiment in August/September 1993 off the coast of Nova Scotia and during the Second Eulerian Model Evaluation Field Study (EMEFSII), in central Ontario in March/April 1990. While no single model stands out as being best or worst, the general tendency is that those models simulating the full oxidant chemistry tend to agree best with observations although differences in transport and treatment of clouds are important as well.

Adsorption of sulfate ions on monocrystalline copper electrodes: the structural effects

Adsorption of sulfate ions on the three basal planes of monocrystalline copper electrodes in 0.1 M HClO 4 was studied by radiometric and electrochemical methods. Also, the copper electrode activity for hydrogen ion discharge was investigated. To check the order of copper surfaces the underpotential deposition of lead was applied. Adsorption of sulfate ions on all four surfaces was found to be reversible with respect to the potential and bulk solution concentration of sulfate. Adsorption isotherms were determined radiometrically. The Gibbs energy of adsorption was calculated by fitting the Henry, Frumkin and virial isotherm equations to the experimental data points. The limiting surface concentration of sulfate ions decreases in the sequence: Cu(111)>Cu(110)>Cu(poly)>Cu(100). The highest value of surface concentration of sulfate for the (111) plane can be accounted for by a match between the tetrahedral structure of the anion and the trigonal distribution pattern of the surface atoms of copper on this plane.

The adsorption of sulfate on gold(111) in acidic aqueous media: adlayer structural inferences from infrared spectroscopy and scanning tunneling microscope

The potential-dependent adsorption of sulfate on ordered Au(111) from acidic aqueous electrolytes has been examined in situ by means of IR reflection-absorption spectroscopy (IRAS) and by atomic-resolution scanning tunneling microscopy (STM) in order to explore further the nature of the adsorbate bonding and the structural changes attending the formation of the ordered adlayer at high potentials, as observed recently using STM. Solution conditions that encompassed aqueous sulfuric acid, sulfuric acid/sulfate electrolytes of varying pH and dilute sulfate in excess perchloric acid were selected in order to facilitate comparisons with recent adsorbate compositional data extracted from chronocoulometric and radiotracer measurements which utilized the last mentioned type of electrolyte. Essentially the same ordered adlayer structures were deduced by STM to form at suitably high potentials (≳ 0.8 V/SCE) in both sulfuric acid and the mixed sulfate/excess perchloric acid media. The adlayer, which exhibits a (√3 × √7) symmetry, involves a fractional sulfate coverage of 0.2, in accordance with chronocoulometic and radiotracer data. The possibility that the ordered sulfate adlayer incorporates coadsorbed hydronium cations is discussed; such coadsorption is suggested by the presence of additional tunneling maxima in the STM images. The IRAS data display a prominent SO stretching band ν so at 1155–1220 cm −1, the potential-dependent intensity of which correlates with sulfate surface concentrations reported earlier. The appearance of this ν so feature is also insensitive to the electrolyte conditions, including pH, consistent with its assignment to adsorbed sulfate rather than bisulfate. The ν so frequency exhibits only a slight (ca. 5 cm −1) downshift upon forming the ordered adlayer, indicating that adsorbate ordering incurs no marked changes in sulfate speciation or surface bonding.