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[en] A temperature stepped-combustion method for separating soil organic carbon (SOC) fractions and their 14C ages was developed to investigate SOC fixation and stability in soils. After acid-leaching, SOC was sequentially oxidized, and extracted from three temperature intervals: (1) 25-400 °C, (2) 400-600 °C, and (3) 600-900 °C. The acid-soluble carbon and SOC released below 600 °C are labile components, with relatively younger 14C ages, while the SOC released above 600 °C is stable with older 14C ages. We applied this method in a grassland, maize cropland and forest nursery cropland, to assist in understanding the stability of carbon in soils under different land use conditions. (author)
[en] Globally, millions of tons of coal fly ash (CFA) are generated per year, and the majority of this material is usually stored in stock piles or landfills, and in a long-term, it can be an environmental hazard if rainwater infiltrates the ashes. Long-term leaching studies of Brazilian ashes are scarce. The purpose of this study was to evaluate arsenic, cadmium, molybdenum, lead, and zinc leaching behavior from a Brazilian CFA by a column experiment designed to simulate field conditions: slightly acid rain considering seasonality of precipitation and temperature for a long-term leaching period (336 days). All elements were leached from CFA, except lead. Elements leaching behavior was influenced by leaching time, leaching volume, and temperature. Higher leachability of As and Cd from CFA during warm and wet season was observed. Results indicate a potential risk to soil and groundwater, since ashes are usually stored in uncovered fields on power plants vicinity.
[en] Environmental regulations affect employment through productivity output and factor substitution. This paper employs a difference-in-differences (DID) method to investigate the effect of China’s Two Control Zones (TCZ) policy on the urban employment in 287 cities from 1994 to 2009. We apply the DID method to two time points: 1998 for policy issuance and 2000 for the policy implementation. From the results of analyses on full-sample cities, the TCZ policy did not contribute to increasing total urban employment. Moreover, a negative impact on employment resulted from sulfur dioxide and acid rain controls in secondary and tertiary industries, respectively. In the acid rain control zone, the TCZ policy increased the average wage of urban workers. Negative effects on employment were observed in larger cities. The policy triggered labor migration from larger to smaller cities, resulting in significant increases in primary and tertiary industry employment in smaller cities, although the effects on mid-size cities were insignificant. This study provides important empirical evidence and insight into the impact of the TCZ policy on urban employment.
[en] Our goal was to reconstruct soil recovery from Acid Rain based upon removal of stemflow at beech (Fagus sylvatica) stands of known historic and recent soil status. Fourteen beech stands in the Vienna Woods were selected in 1984 and again in 2012 to study changes in soil and foliar chemistry over time. A part of those stands had been strip cut, and to assess reversibility of soil acidification, we analyzed soils around beech stumps from different years of felling, representing the years when acidic stemflow ceased to affect the soil. Furthermore, it was hypothesized that changes of soil chemistry are reflected in the stemwood of beech. Half-decadal samples of tree cores were analyzed for Ca, Mg, K, Mn, Fe, and Al. Soil analyses indicated recovery in the top soil of the stemflow area but recovery was delayed in the between trees areas and deeper soil horizons. Differences in soil pH between proximal and distal area from beech stumps were still detectable after 30 years indicating that soils may not recover fully from acidification or do so at a rather slow rate. Stemwood contents indicated mobilization of base cations during the early 80s followed by a steady decrease thereafter. Backward reconstructions of soil pH and soil nutrients, building on regressions between recent stemwood and soil chemistry, could not be verified by measured soil data in 1984, but matched with declining cation foliar contents from 1984 to 2012. Dendrochemical reconstructions showed highest values in the 1980s, but measured soil exchangeable cation contents were clearly lower in 1984. Hence, we conclude that our reconstructions mimicked soil solution rather than soil exchanger chemistry.
[en] Atmospheric precipitation is a very important link in the water cycle. The characteristics of major ions (n = 341) and stable isotopes (δ2H, δ18O; n = 157) were analysed in Hangzhou and Huzhou, which are economically prosperous cities in East China. The δ2H and δ18O values of precipitation ranged from − 109.70 to 21.30‰ and from − 14.87 to − 0.95‰, respectively. Compared with the local meteoric water line (LMWL) of China, the slope and intercept of the LMWL were much higher in Hangzhou and Huzhou, which is related to the effects of the humid climate and less secondary evaporation. The δ2H and δ18O values were highest in spring because of the influence of air masses from the northern Asian continent and other nearby sources. In contrast, the air masses from the South China Sea and the western Pacific Ocean in the summer had the lowest δ2H and δ18O. The dominant ions in precipitation indicate that Ca2+, HCO3−, SO42−, NH4+ and NO3− are the main ions of precipitation in Hangzhou and Huzhou, and the dilution of precipitation leads to lower concentrations of ions in spring and summer, similar to the values found in most Chinese cities. The increase in motor vehicle use resulted in a lower [SO42−]/[NO3−] ratio (1.64) of precipitation, indicating mixed acid rain in Hangzhou and Huzhou (HZS). Based on a combination of the correlation analysis, enrichment factors and source contributions, we determined that SO42− and NO3− were introduced mainly from anthropogenic activities such as coal combustion and vehicle exhaust, accounting for 89% and 99%, respectively. The strong correlation between Cl− and Na+, as well as Ca2+, Mg2+ and K+, indicates that these ions commonly have marine and crustal origins, respectively, and 40% of Mg2+ comes from a marine source.
[en] A gas sensor is a device used to monitor and quantify the leakage or presence of harmful gases in the environment. The NO2 is mainly emitted from vehicle exhausts, industrial chimneys, and combustion of fossil fuels. It is among the harmful gases which are danger to human beings and is the cause of acid rain. Metal oxides (MOs) have been proven to be effective gas sensors, however, their high operating temperature hampers their practical use. Hence, MOs supported upon graphene-based materials tend to have low operating temperatures since graphene provides a large number of active sites for gas adsorption upon MO surface. It also facilitates charge transfer from MO surface to adsorbed gas molecules. On the other hand, graphene-based materials have high selectivity for NO2. Upon functionalization of graphene with –SO3H groups tend to reduce the response and recovery time of the sensor. Also sensing of NO2 by MO depends upon its p-type or n-type nature. The p-type MOs do not have a better response for NO2 than n-type sensors, however, upon compositing them with functionalized graphene, their response enhances and they show better selectivity towards NO2. Also, creating defects like oxygen vacancies tend to lower the operating temperature of MO-based gas sensors and makes them more selective towards NO2. In this minor review, MO-based sensors for room temperature sensing of NO2 have been discussed taking into account their response, recovery time, sensitivity and selectivity.
[en] Chemicals leached from concrete are an important way that urban stormwater can influence water quality. In this study, we evaluated the weathering properties of sidewalk samples and tested how carbonation (exposure to elevated levels of gaseous CO2) can be used to simulate natural aging of concrete. The experiments focused on acid neutralizing capacity (ANC), which is known to be released by concrete in large amounts, and Cr(VI), because of its established carcinogenicity and prevalence in concrete. Chemical weathering of crushed sidewalk samples was measured with upflow recirculating columns carrying simulated acid rain. The weathering rate of ANC from four different samples was found to decrease after 1 week of exposure to a 5% carbon dioxide atmosphere and to remain constant thereafter through 8 weeks of carbonation treatment. In contrast, weathering of chromium (VI) increased after exposure to a 5% carbon dioxide atmosphere for 1 week, though it also remained stable from then through 8 weeks of carbonation. Almost all ions approached steady state after 2.5 h in the recirculation columns irrespective of carbonation time. The main contributor of ANC was Ca2+ ion, though this was partly balanced by an unexpectedly high amount of SO42−. A notable exception to the temporal leaching pattern was largely un-ionized Si, which continued to increase in concentration for at least 3 days of recirculation. Si levels were also higher than is generally observed for aluminosilicate weathering in small watersheds, a novel finding.
[en] A pot experiment and a leaching experiment were conducted to investigate the effects of earthworms and pig manure on heavy metals (Cd, Pb, and Zn) immobility, in vitro bioaccessibility and leachability under simulated acid rain (SAR). Results showed manure significantly increased soil organic carbon (SOC), dissolved organic carbon (DOC), available phosphorus (AP), total N, total P and pH, and decreased CaCl2-extractable metals and total heavy metals in water and SAR leachate. The addition of earthworms significantly increased AP (from 0.38 to 1.7 mg kg−1), and a downward trend in CaCl2-extractable and total leaching loss of heavy metals were observed. The combined earthworm and manure treatment decreased CaCl2-extractable Zn, Cd, and Pb. For Na4P2O7-extractable metals, Cd and Pb were decreased with increasing manure application rate. Application of earthworm alone did not contribute to the remediation of heavy metal polluted soils. Considering the effects on heavy metal immobilization and cost, the application of 6% manure was an alternative approach for treating contaminated soils. These findings provide valuable information for risk management during immobilization of heavy metals in contaminated soils.
[en] Non-renewable energy sources have detrimental environmental effects, which directly and indirectly affect the biosphere as environmental deposits from their use for energy generation exceed a threshold. This study performs a streamlined life cycle assessment (LCA) of a coal-fired plant in South Africa. The cradle-to-grave LCA focuses on the coal cycle to determine hotspots with high environmental impacts in the process. Four impact categories were considered in this study: global warming potential, photochemical ozone creation potential, eutrophication potential, and acidification potential. Coal transportation, coal pulverization, water use, and ash management were identified as hotspots in the coal cycle. The coal process has 95% potential for global warming, 4% potential for eutrophication, 1% potential for acidification, and a negligible percentage for photochemical ozone creation. Susceptibility to climate change, eutrophication, acid rain, soil degradation, and water contamination among others are major concerns of the coal cycle. Outsourcing coal from nearby mines with train as medium of transportation reduces environmental impact. Similarly, the use of mitigation technologies like flue gas desulphurization, carbon capture storage, or selective catalytic reduction will reduce the concentration of the flue gas emitted. Ultimately, substituting the coal process with renewable energy sources will ensure environmental sustainability in South Africa. This study will serve as a good resource for further studies on LCA of coal power plants not only in other African countries but in other developing countries with similar situation.
[en] A common basic assumption in civil engineering is that rainwater is chemically neutral (pH = 7.0). However, even under pristine conditions, rainwater is often more acidic due to natural emissions of organic acids. Even natural rain acidity may be very aggressive against natural stones and concrete. A harmful impact of UV radiation on the concrete durability was discussed by the authors for the first time in 2006. The objective of the current research was the characterization of weathering processes occurred in the wet cast concrete subjected to the normal acidic rain and UV radiation, and the evaluation of their possible effect on the reinforced concrete durability. It was revealed that organic acids contained in rain of the natural acidity promote an intense concrete carbonation, even when a permeability of concrete looks to be low.