Modeling Urban PM<Subscript>2.5</Subscript> Concentration by Combining Regression Models and Spectral Unmixing Analysis in a Region of East China

Understanding the spatial distribution of PM_2.5 concentration and its contributing environmental variables is critical to develop strategies of addressing adverse effects of the particulate pollution. In this study, a range of meteorological and land use factors were incorporated into a linear regression (LR) model and a logistic model-based regression (LMR) model to simulate the annual and winter PM_2.5 concentrations. The vegetation cover, derived from a linear spectral unmixing analysis (LSUA), and the normalized difference built-up index (NDBI), were found to improve the goodness of fit of the models. The study shows that (1) both the LR and the LMR agree on the predicted spatial patterns of PM_2.5 concentration and (2) the goodness of fit is higher for the models established based on the annual PM_2.5 concentration than that based on the winter PM_2.5. The modeling results show that higher PM_2.5 concentration coincided with the major urban area for the annual average but focused on the suburban and rural areas for the winter. The methods introduced in this study can potentially be applied to similar regions in other developing countries.     

Diurnal Characteristics of Suspended Particulate Matter and PM<Subscript>2.5</Subscript> in the Urban and Suburban Atmosphere of the Kanto Plain,Japan

Suspended particulate matter (SPM) and PM_2.5 in the urban and suburban atmosphere of the Kanto Plain of Japan, which includes the Tokyo metropolitan area, during the period 22–26 July 2002 were characterized. Samples of SPM and PM_2.5 were collected by low-volume samplers at 6-h intervals at Suginami, Saitama, and Kisai. At all the sites, the major components of SPM and PM_2.5 were organic carbon (OC), elemental carbon (EC), and sulfate. The ion balance, the size distributions of the ionic species, and the high correlation between SO₄ ^2? and NH₄ ⁺ indicated that the main chemical form of sulfate was (NH₄)₂SO₄. The OC/EC ratios were larger in the daytime than in the nighttime. The correlation coefficients of OC, OC/EC, and SO₄ ^2? with ozone concentrations at inland sites (Saitama, Kisai) were higher than those at the coastal site (Suginami). Bound water and hydrogen and oxygen atoms associated with OC, the amounts of which were estimated with a mass closure model, contributed substantially to the total particle mass. The chemical characteristics of the particles indicated that two mechanisms led to high concentrations of SPM and PM_2.5: (i) an active photochemical process produced high concentrations of OC and sulfate, leading to a high concentration of (NH₄)₂SO₄ in the particles and to production of secondary organic aerosols; (ii) stable meteorological conditions resulted in accumulation of primary particles, mainly emitted from vehicle exhaust, resulting in high concentrations of OC and EC.     

Improved Photodegradation Efficiency of 2,4-DCP Through a Combined Q<Subscript>3</Subscript>Fe(III)-Decorated Porous g-C<Subscript>3</Subscript>N<Subscript>4</Subscript>/H<Subscript>2</Subscript>O<Subscript>2</Subscript> System

Graphitic carbon nitride (g-C₃N₄) is a photocatalyst with wide application in removal of organic pollutants. In this study, we designed a porous g-C₃N₄ (p-g-C₃N₄)/8-quinolinolato iron(III) (Q₃Fe)/H₂O₂ system to enhance the organic pollutant removal efficiency by combining photocatalysis and Fenton interaction under neutral condition. The p-g-C₃N₄ was prepared through a two-step thermal oxidation reaction. Afterwards, Q₃Fe-coupled p-g-C₃N₄ was prepared by an impregnating method. The 2,4-dichlorophenol (2,4-DCP) photodegradation ratio and decomposition rate of the p-g-C₃N₄/Q₃Fe/H₂O₂ system are approximately 5 and 18 times as high as those of individual p-g-C₃N₄ system, respectively. Besides, its degradation rate is 4.3 times as high as that in the p-g-C₃N₄/H₂O₂ system. Meanwhile, Q₃Fe/g-C₃N₄ also exhibits higher activity than individual p-g-C₃N₄ in 2,4-DCP photo-decomposing. On the basis of the results of the radical trapping experiments and the Fe(II) concentration in different systems, the synergistic effect between photocatalysis and Fenton reaction is vital for the efficient pollutant degradation. The coupled system combining p-g-C₃N₄ with Q₃Fe and H₂O₂ shows potential for efficient treatment of recalcitrant organic pollutants. The combined system in this work indicated a new idea for the decomposition of organic pollutants.     

Response of CH<Subscript>4</Subscript> oxidation and methanotrophic diversity to NH<Subscript>4</Subscript><Superscript>+</Superscript> and CH<Subscript>4</Subscript> mixing ratios

Methane oxidising activity and community structure of 11, specifically targeted, methanotrophic species have been examined in an arable soil. Soils were sampled from three different field plots, receiving no fertilisation (C), compost (G) and mineral fertiliser (M), respectively. Incubation experiments were carried out with and without pre-incubation at elevated CH₄ mixing ratios (100 ml CH₄ l⁻¹) and with and without ammonium (100 mg N kg⁻¹) pre-incubation. Four months after fertilisation, plots C, G and M did not show significant differences in physicochemical properties and CH₄ oxidising activity. The total number of methanotrophs (determined as the sum the 11 specifically targeted methanotrophs) in the fresh soils was 17.0×10⁶, 13.7×10⁶ and 15.5×10⁶ cells g⁻¹ for treatment C, G and M, respectively. This corresponded to 0.11 to 0.32% of the total bacterial number. The CH₄ oxidising activity increased 10⁵-fold (20–26 mg CH₄ g⁻¹ h⁻¹), the total number of methanotrophs doubled (28–76×10⁶ cells g⁻¹) and the methanotrophic diversity markedly increased in treatments with a pre-incubation at elevated CH₄ concentrations. In all soils and treatments, type II methanotrophs (62–91%) outnumbered type I methanotrophs (9–38%). Methylocystis and Methylosinus species were always most abundant. After pre-incubation with ammonium, CH₄ oxidation was completely inhibited; however, no change in the methanotrophic community structure could be detected.     

Solar Decolorization of Methylene Blue by Magnetic MgFe<Subscript>2</Subscript>O<Subscript>4</Subscript>-MWCNT/Ag<Subscript>3</Subscript>VO<Subscript>4</Subscript> Visible Active Photocatalyst

MgFe₂O₄-MWCNT/Ag₃VO₄ photocatalyst was prepared for benefiting the visible region of solar spectrum. Prepared catalyst was characterized by using scanning electron microscope (SEM), X-ray diffraction (XRD), and energy-dispersive X-ray spectroscopy (EDX). Photocatalytic activity was measured by methylene blue (MB) decolorization under visible light obtained from a 105-W tungsten light bulb. Dye decolorization and its kinetics were followed up by means of a UV-vis spectrophotometer. Kinetic model of decolorization was found to be compatible with first-order kinetics. The effects of pH and concentration of MB solution on the decolorization efficiency were determined. Low and high pH conditions were found to be more effective in increasing the MB decolorization yield and rate. On the other hand, due to the low transparency of concentrated MB solutions, an increase on decolorization time and a lowering in decolorization yield were encountered. Thanks to the magnetic MgFe₂O₃ nanoparticles, 96% of the catalyst could be recovered by a simple magnetic bar. It was observed that simulated wastewater containing MB was also successfully decolorized showing that visible region-sensitive MgFe₂O₄-MWCNT/Ag₃VO₄ photocatalyst can be benefited as a potential, efficient, and reusable material for the removal organic pollutants in aquatic environment.     

Preparation of Highly Efficient CoFe<Subscript>2</Subscript>O<Subscript>4</Subscript>/Zn<Subscript>2</Subscript>SnO<Subscript>4</Subscript> Composite Photocatalyst for the Degradation of Rhodamine B Dye from Aqueous Solution

CoFe₂O₄/Zn₂SnO₄ composite was synthesized using a simple two-step process and applied as a novel-efficient photocatalyst for the rhodamine B degradation from aqueous solution. Characterization techniques such as X-ray diffraction (XRD), N₂ adsorption-desorption isotherms, scanning electron microscopy (SEM), EDS analysis, and diffuse reflectance spectroscopy were employed in order to investigate the physical and chemical properties of composite. Higher values of the specific surface area, pore volume and diameter, and a smaller band-gap energy promoted a greater catalytic activity of CoFe₂O₄/Zn₂SnO₄ composite when compared to Zn₂SnO₄. A rapid decolorization of dye solution was observed at 40 min of reaction using the CoFe₂O₄/Zn₂SnO₄ catalyst, being 2.5 times faster than the Zn₂SnO₄ alone. Therefore, the CoFe₂O₄/Zn₂SnO₄ composite shows extraordinarily high photocatalytic activity toward the degradation of rhodamine B dye from aqueous solution.     

Effect of CO<Subscript>2</Subscript> on nitrification and immobilization of NH<Subscript>4</Subscript><Superscript>+</Superscript>-N

A laboratory incubation experiment was conducted to demonstrate that reduced availability of CO₂ may be an important factor limiting nitrification. Soil samples amended with wheat straw (0%, 0.1% and 0.2%) and (¹⁵NH₄)₂SO₄ (200 mg N kg^–1 soil, 2.213 atom% ¹⁵N excess) were incubated at 30±2°C for 20 days with or without the arrangement for trapping CO₂ resulting from the decomposition of organic matter. Nitrification (as determined by the disappearance of NH₄⁺ and accumulation of NO₃^–) was found to be highly sensitive to available CO₂ decreasing significantly when CO₂ was trapped in alkali solution and increasing substantially when the amount of CO₂ in the soil atmosphere increased due to the decomposition of added wheat straw. The co-efficient of correlation between NH₄⁺-N and NO₃^–-N content of soil was highly significant (r =0.99). During incubation, 0.1–78% of the applied NH₄⁺ was recovered as NO₃^– at different incubation intervals. Amendment of soil with wheat straw significantly increased NH₄⁺ immobilization. From 1.6% to 4.5% of the applied N was unaccounted for and was due to N losses. The results of the study suggest that decreased availability of CO₂ will limit the process of nitrification during soil incubations involving trapping of CO₂ (in closed vessels) or its removal from the stream of air passing over the incubated soil (in open-ended systems).     

Soil nitrogen mineralization and fate of (<Superscript>15</Superscript>NH<Subscript>4</Subscript>)<Subscript>2</Subscript>SO<Subscript>4</Subscript> in field-incubated soil in a hardwood plantation of subtropical Australia: the effect of mulching

Background, aim, and scope  

Mulching is frequently used to overcome the drought problem in hardwood plantations that are increasingly being established in lower rainfall areas of Queensland, Australia because of increasing land values. In addition to soil water content, soil nitrogen (N) availability is another critical determinant of plantation productivity in these areas. The purpose of this study was to understand how soil mineral N dynamics, in situ N mineralization, and the fate of fertilized N would be affected by mulching during the early establishment of hardwood plantations.     

Reducing CH<Subscript>4</Subscript> and CO<Subscript>2</Subscript> emissions from waterlogged paddy soil with biochar

Purpose  

A potential means to diminish increasing levels of CO₂ in the atmosphere is the use of pyrolysis to convert biomass into biochar, which stabilizes the carbon (C) that is then applied to soil. Before biochar can be used on a large scale, especially in agricultural soils, its effects on the soil system need to be assessed. This is especially important in rice paddy soils that release large amounts of greenhouse gases to the atmosphere.     

The Content of As and Heavy Metals in TSP and PM<Subscript>10</Subscript> Near Copper Smelter in Bor,Serbia

The content of As and heavy metals (Pb, Cd, Ni, and Cu) in total suspended particulate (TSP) and PM₁₀ at 3 locations (Park, Institute, and Jugopetrol) near the copper smelter in Bor (Serbia) has been analyzed within the period 2004 to 2015 with the aim of investigating the seasonal and spatial changes of those pollutants in the suspended particles. The content of As in TSP and PM₁₀ was over the annual EU limit value at all measuring points during the entire period of observation, while contents of Cd and Pb were periodically above the annual EU limits. There were no statistically significant seasonal changes between mean levels of the observed elements in the cold (October–March) and warm (April–September) periods during the year. A strong and moderate positive correlation was detected between the concentrations of each particular element (except Ni) at all measuring points. Additionally, Cd was the most enriched element followed by Pb, As, and Cu, while Ni was low-enriched. The constant air pollution with As particles, sometimes in concentrations even 20 times higher than the permitted annual value, requires urgent undertaking of concrete actions in order to reduce anthropogenic emission of suspended particles in Bor.     

Porous Materials Modified with Fe<Subscript>3</Subscript>O<Subscript>4</Subscript> Nanoparticles for Arsenic Removal in Drinking Water

The contamination of drinking water with arsenic has been a problem in a lot of countries around the world because of its toxicological and carcinogenic effects on human health. Porous materials modified with Fe₃O₄ nanoparticles (Fe₃O₄ NPs) represent convenient removers for that contaminant. A co-precipitation method of Fe(III) and Fe(II) in alkaline media was applied to obtain Fe₃O₄ NPs. In a first stage, single nanoparticles were synthesized and stabilized with carboxylic acids. A characterization with attenuated total reflectance Fourier transform infrared spectroscopy (ATR-FTIR), Raman spectroscopy, and X-ray diffraction (XRD) confirms a magnetite-type structure. Moreover, transmission electron microscopy (TEM) and calculations from XRD data using Scherrer’s equation indicate an average particle size of 13 nm and an average crystallite size of 10 nm, both independent of the stabilizer used. Then, the co-precipitation method studied was applied to modify kaolin, bentonite, diatomite, and silica and thus prepare magnetic composites having support-magnetite weight ratios of 2:1. Among them, silica-modified material presented the best hydraulic characteristics, an important aspect for large-scale applications such as removal under gravity. This composite has the capacity to remove up to 80 and 70% for initial concentrations of 25 and 50 μg/L, respectively, representing a convenient remover for processes developed in subsequent stages or in continuous flow.     

Net and gross mineral N production rates at three levels of forest canopy retention: evidence that NH<Subscript>4</Subscript><Superscript>+</Superscript> and NO<Subscript>3</Subscript><Superscript>−</Superscript> dynamics are uncoupled

Alternative silvicultural systems were introduced in Coastal Western Hemlock forests of British Columbia, Canada, to reduce disturbance incurred by conventional clear-cutting and to maintain the forest influence on soil nutrient cycling. As we hypothesized, in situ pools and net mineralization of NH₄ ⁺ were lower under no and low disturbance (old-growth forest and shelterwood) compared to clear-cuts (high disturbance); in situ pools and net production of NO₃ ⁻ were very low across all treatments. Gross transformation rates of NH₄ ⁺ increased while those of NO₃ ⁻ decreased with increasing disturbance, suggesting that these processes were uncoupled. We conclude that shelterwood harvesting reduces the impact on forest floor NH₄ ⁺ cycling compared to clear-cutting, and that neither low nor high disturbance intensity results in substantial NO₃ ⁻ accumulation, as what occasionally occurs in other ecosystems. We hypothesize that the uncoupling of NH₄ ⁺ and NO₃ ⁻ dynamics may be due to the predominance of heterotrophic nitrification by lignin-degrading fungi that oxidize organic N rather than NH₄ ⁺–N, and whose activities are suppressed at high NH₄ ⁺ concentrations.     

Changes in the system of chemical bonds in gibbsite under the impact of NH<Subscript>4</Subscript>H<Subscript>2</Subscript>PO<Subscript>4</Subscript> solutions of different concentrations

The participation of anionic aluminum hydroxo complexes in the binding of phosphate anions on the surface of gibbsite has been shown. The succession of changes in the anionic aluminum phosphate complexes under increasing concentration of phosphate solution has been studied. It has been found that aluminum polyphosphate complexes responsible for the intensive dissolution of gibbsite are formed, along with aluminum orthophosphate complexes, at phosphate solution concentrations of 1 and 2 mol P/L. The decisive role of polyphosphate (P–O–P) groups in the ligand structure of anionic complexes in the transformation of gibbsite to a phosphate mineral (ammonium taranakite) has been revealed. The role of hydrogen bonds with the participation of ligand P(O)OH groups in the formation of ammonium taranakite crystals has been discussed.     

N<Subscript>2</Subscript>O,CO<Subscript>2</Subscript>, Production,and C Sequestration in Vineyards: a Review

Even if it is less polluting than other farm sectors, grape growing management has to adopt measures to mitigate greenhouse gas (GHG) emissions and to preserve the quality of grapevine by-products. In viticulture, by land and crop management, GHG emissions can be reduced through adjusting methods of tillage, fertilizing, harvesting, irrigation, vineyard maintenance, electricity, natural gas, and transport until wine marketing, etc. Besides CO₂, nitrous oxide (N₂O) and methane (CH₄), released from fertilizers and waste/wastewater management are produced in vineyards. As the main GHG in vineyards, N₂O can have the same harmful action like large quantities of CO₂. Carbon can be found in grape leaves, shoots, and even in fruit pulp, roots, canes, trunk, or soil organic matter. C sequestration in soil by using less tillage and tractor passing is one of the efficient methods to reduce GHG in vineyards, with the inconvenience that many years are needed for detectable changes. In the last decades, among other methods, cover crops have been used as one of the most efficient way to reduce GHG emissions and increase fertility in vineyards. Even if we analyze many references, there are still limited information on practical methods in reducing emissions of greenhouse gases in viticulture. The aim of the paper is to review the main GHG emissions produced in vineyards and the approached methods for their reduction, in order to maintain the quality of grapes and other by-products.     

A comparison of soil food webs beneath C<Subscript>3</Subscript>- and C<Subscript>4</Subscript>-dominated grasslands

Soil food webs influence organic matter mineralization and plant nutrient availability, but the potential for plants to capitalize on these processes by altering soil food webs has received little attention. We compared soil food webs beneath C₃- and C₄-grass plantings by measuring bacterial and fungal biomass and protozoan and nematode abundance repeatedly over 2 years. We tested published expectations that C₃ detritus and root chemistry (low lignin/N) favor bacterial-based food webs and root-feeding nematodes, whereas C₄ detritus (high lignin/N) and greater production favor fungal decomposers and predatory nematodes. We also hypothesized that seasonal differences in plant growth between the two grassland types would generate season-specific differences in soil food webs. In contrast to our expectations, bacterial biomass and ciliate abundance were greater beneath C₄ grasses, and we found no differences in fungi, amoebae, flagellates, or nematodes. Soil food webs varied significantly among sample dates, but differences were unrelated to aboveground plant growth. Our findings, in combination with previous work, suggest that preexisting soil properties moderate the effect of plant inputs on soil food webs. We hypothesize that high levels of soil organic matter provide a stable environment and energy source for soil organisms and thus buffer soil food webs from short-term dynamics of plant communities.     

Suppression of NH<Subscript>3</Subscript> and N<Subscript>2</Subscript>O emissions by massive urea intercalation in montmorillonite

Purpose  

A large amount of nitrogen (N) fertilizers has been broadcasted over soil surface for reliable crop production. Unfortunately, the broadcasted N vulnerable to volatilization and leaching can lead to serious environmental problems. As a new approach to mitigate N loss of broadcasted fertilizers, massive intercalation of urea into montmorillonite (MMT) was recently proposed to innovatively enhance the urea use efficiency. This study focuses on demonstrating the behaviors of the urea intercalated into MMT in soils.     

Effects of biochar addition on N<Subscript>2</Subscript>O and CO<Subscript>2</Subscript> emissions from two paddy soils

Impacts of biochar addition on nitrous oxide (N₂O) and carbon dioxide (CO₂) emissions from paddy soils are not well documented. Here, we have hypothesized that N₂O emissions from paddy soils could be depressed by biochar incorporation during the upland crop season without any effect on CO₂ emissions. Therefore, we have carried out the 60-day aerobic incubation experiment to investigate the influences of rice husk biochar incorporation (50 t ha⁻¹) into two typical paddy soils with or without nitrogen (N) fertilizer on N₂O and CO₂ evolution from soil. Biochar addition significantly decreased N₂O emissions during the 60-day period by 73.1% as an average value while the inhibition ranged from 51.4% to 93.5% (P < 0.05–0.01) in terms of cumulative emissions. Significant interactions were observed between biochar, N fertilizer, and soil type indicating that the effect of biochar addition on N₂O emissions was influenced by soil type. Moreover, biochar addition did not increase CO₂ emissions from both paddy soils (P > 0.05) in terms of cumulative emissions. Therefore, biochar can be added to paddy fields during the upland crop growing season to mitigate N₂O evolution and thus global warming.     

The effect of moisture on nitrous oxide emissions from soil and the N<Subscript>2</Subscript>O/(N<Subscript>2</Subscript>O+N<Subscript>2</Subscript>) ratio under laboratory conditions

Nitrous oxide (N₂O) contributes to greenhouse effect; however, little information on the consequences of different moisture levels on N₂O/(N₂O+N₂) ratio is available. The aim of this work was to analyze the influence of different soil moisture values and thus of redox conditions on absolute and relative emissions of N₂O and N₂ at intact soil cores from a Vertic Argiudoll. For this reason, the effect of water-filled porosity space (WFPS) values of soil cores of 40, 80,100, and 120% (the last one with a 2-cm surface water layer) was investigated. The greatest N₂O emission occurred at 80% WFPS treatment where conditions were not reductive enough to allow the complete reduction to N₂. The N₂O/(N₂O+N₂) ratio was lowest (0–0.051) under 120% WFPS and increased with decreasing soil moisture content. N₂O/(N₂O+N₂) ratio values significantly correlated with soil Eh; redox conditions seemed to control the proportion of N gases emitted as N₂O. N₂O emissions did not correlate satisfactorily with N₂O/(N₂O+N₂) ratio values, whereas they were significantly explained by the amount of total N₂O+N₂ emissions.     

Activated Biochar Prepared by Pomelo Peel Using H<Subscript>3</Subscript>PO<Subscript>4</Subscript> for the Adsorption of Hexavalent Chromium: Performance and Mechanism

Adsorption of hexavalent chromium (Cr(VI)) using pomelo peel activated biochar (PPAB) as a adsorbent was investigated. The characterization of the adsorbent was studied by Brunauer-Emmett-Teller (BET), thermogravimetric analysis (TGA), X-ray diffraction (XRD), and zeta potentials analysis. The results showed that the PPAB had a high microporous structure and the existence of organic compounds such as hemicellulose, cellulose, and lignin. Various parameters including initial Cr(VI) concentration, pH, and adsorbent dosage were studied. The results indicated that the adsorption process was pH dependent and maximum adsorption capacity of Cr(VI) was 57.637 mg/g at pH 2.0 and 35 °C with PPAB dosage of 0.05 g. The adsorption kinetics fitted well to the pseudo-second-order model and the correlation coefficients were greater than 0.999. The adsorption isotherm data could be better described with the Langmuir model, suggesting the homogeneous and monolayer adsorption. Moreover, the scanning electron microscopy (SEM), energy dispersive spectrometry (EDS), and Fourier transform infrared spectrum (FTIR) results showed that the surface of PPAB had plenty of developed pores after activation and the modification process was deemed to proceed between the O–H groups from pomelo peel and H₃PO₄ molecules. The main adsorption mechanism was attributed electrostatic interaction and ion exchange between the surface of PPAB and Cr(VI).