Modeling the carbon cycle of urban systems

Although more than 80% of carbon dioxide emissions originate in urban areas, the role of human settlements in the biosphere evolution and in global carbon cycling remains largely neglected. Understanding the relationships between the form and pattern of urban development and the carbon cycle is however crucial for estimating future trajectories of greenhouse gas concentrations in the atmosphere and can facilitate mitigation of climate change. In this paper I review state-of-the-art in modeling of urban carbon cycle. I start with the properties of urban ecosystems from the ecosystem theory point of view. Then I discuss key elements of an urban system and to which degree they are represented in the existing models. In conclusions I highlight necessity of including biophysical as well as human related carbon fluxes in an urban carbon cycle model and necessity of collecting relevant data.     

北太平洋地区春季粉尘的空间分布特征——观测及模拟

通过对2001年4月的一次中亚强沙尘暴过程的观测事实分析和数值模拟,结果表明,源自中亚的强沙尘暴扬起的粉尘,通过西风急流远程传输到韩国、日本、北太平洋、北美大陆.北太平洋地区的沙尘沉积通量空间分布将主要取决于3个方面:沙尘沉积通量随传输距离的增加呈指数衰减;传输路径上粉尘有较高的沉降通量;沙尘过境时的降水空间格局将在很大程度上决定粉尘的沉降空间格局.     

生物活性炭纤维处理微污染源水

在生物活性炭的基础上,以活性炭纤维替代颗粒活性炭,研制了生物活性炭纤维(BACF)新型吸附材料,用于处理水中有机污染物。用扫描电镜观察了微生物在ACF上的固定情况,以水处理常用指标CODMn、UV254及,GC-MS图谱分析考察BACF对于微污染源水的处理效果。研究结果显示BACF技术作为一种新颖的水的深度处理工艺,结合了吸附与生物降解的双重效能,可以有效提高对源水的净化效果,提高出水水质,同时也可以扩大水源水的取水范围,是一项先进的水处理技术。     

Electric Swing Adsorption for CO2 removal from flue gases

One of the most important sources of CO₂ emissions are the fossil-fuel fired plants for production of electricity. Removal of CO₂ from flue gas streams for further sequestration has been proposed by the International Panel on Climate Change experts as one of the most reliable solutions to mitigate anthropogenic greenhouse emissions. When natural gas is employed as fuel, the molar fraction of CO₂ in the flue gas is lower than 5% causing serious problems for capture. The purpose of this work is to present experimental validation of an Electric Swing Adsorption (ESA) technology that may be employed for carbon capture for low molar fractions of CO₂ in the flue gas streams. To improve energy utilization, an activated carbon honeycomb monolith with low electrical resistivity was employed as selective adsorbent. A mathematical model for this honeycomb is proposed as well as different ESA cycles for CO₂ capture.     

Effect of steam hydration on performance of lime sorbent for CO2 capture

Lime is considered a feasible sorbent for the capture of CO₂ from large stationary sources. The positive attributes of a natural source material, low cost and lack of harmful by-products are offset by rapid deterioration in performance and high regeneration temperature. Performance can be improved by hydrating the lime using steam. We investigate a steam hydration process wherein lime is hydrated for 5 min at 300 °C and atmospheric pressure in a mixture of steam and CO₂. The experiments consisted of 10 capture cycles with 60% of the lime active at the end. Extrapolation using a decay model suggests a residual carbonation level of 48%, significantly higher than the 8% achieved by dry lime cycles. The cost of replacement sorbent under these conditions is less than $1/t of CO₂ captured. The hydrated lime process also reduces the thermal load, for heating and cooling, by half as well as the inventory, and therefore solids handling, by a factor 5 over dry lime. The introduction of the hydration reaction provides another exothermic reaction for heat management.     

Baseline assessment for environmental services payments from satellite imagery: a case study from Costa Rica and Mexico

In this study we evaluate the accuracy of four global and regional forest cover assessments (MODIS, IGBP, GLC2000, PROARCA) as tools for baseline estimation. We conduct this research at the national scale for Costa Rica and for two tropical dry forest study sites in Costa Rica (Santa Rosa) and Mexico (Chamela-Cuixmala). We found that at the national level, the total forest cover accuracy of the four land cover maps was inflated due to an overestimation of forest in areas with an evergreen canopy. However, the four maps greatly underestimated the extent of the deciduous forest (dry forest); an ecosystem that faces high deforestation pressure and poses complications to the mapping of its extent from remotely sensed data. For the tropical dry forest sites, all maps have low forest cover accuracies (mean for Santa Rosa: 27%; mean for Chamela-Cuixmala: 56%). This has implications for policy implementation.     

Using LCA to evaluate impacts and resources conservation potential of composting: A case study of the Asti District in Italy

Separate collection of municipal solid waste has overcome the 50% threshold in the Asti District in northern Italy, nearly one-third being composed of household and green organic waste. In order to address present and future solutions, it becomes therefore fundamental to assess the environmental performances of the current management of organic waste from separate collection. A from-gate-to-cradle life cycle assessment (LCA) model has been developed by expanding system boundaries, in order to carry out the assessment in the context of the whole waste management streamline. The environmental performances of an existing aerobic plant were made available, based on field measured data, by paying attention to the role and contribution of waste management subsystems. The need for actual and reliable data on materials and energy input, as well as gross and net gains from materials recovery, including benefits arising from use of compost in farming activities, was probably the major drawback that had to be faced. The study integrated the findings of different investigations from the literature with field measured data in order to obtain a more comprehensive framework representative of the area under study. The results may help public administrators to better understand the suitability of using LCA tools when dealing with solid waste management strategies.     

Correlates of mercury in fish from lakes near Clyde Forks, Ontario, Canada

Subsurface soils near Clyde Forks, Ontario, Canada, can have naturally high concentrations of mercury (Hg) from local geological sources. To investigate Hg in local aquatic food webs, Hg was measured in fish dorsal muscle (mainly yellow perch [YP] and pumpkinseed sunfish [PS]) and surface sediments from 10 regional lakes. Water chemistry, along with fork length, weight, and stable isotopes (delta15N, delta13C, delta34S) in fish were also measured. No lake sediments had elevated (>0.3microg/g dw) Hg, and average Hg concentrations in fish were not sufficiently high (<1microg/g dw) to be of concern for fish-eating wildlife. Variance in fish Hg was best explained by dietary carbon source (delta13C), and certain lake variables (e.g., pH for YP). PS with more pelagic feeding habits had higher delta34S and Hg than those with more littoral feeding habits. Potential biological linkages between fish Hg and delta34S, a parameter that may be related to the lake sulphate-reducing bacteria activity, requires further investigation.     

大气SO2与硫酸盐化速率相关斜率的探讨

利用ＳＯ２和硫酸盐化速率相关斜率，推算了有实际意义的总物质移动系数值，并确定了其允许范围，这为各地今后更地建立了硫酸盐化速率和大气ＳＯ２相关性提供技术依据。     

Enhanced activation of peroxymonosulfate by CNT-TiO2 under UV-light assistance for efficient degradation of organic pollutants

CNT-TiO₂ composite is used to activate PMS under UV-light assistance. Superior performance is due to the enhanced electron-transfer ability of CNT. SO₄•⁻, •OH and ¹O₂ play key roles in the degradation of organic pollutants. In this work, a UV-light assisted peroxymonosulfate (PMS) activation system was constructed with the composite catalyst of multi-walled carbon nanotubes (CNT) - titanium dioxide (TiO₂). Under the UV light irradiation, the photoinduced electrons generated from TiO₂ could be continuously transferred to CNT for the activation of PMS to improve the catalytic performance of organic pollutant degradation. Meanwhile, the separation of photoinduced electron-hole pairs could enhance the photocatalysis efficiency. The electron spin resonance spectroscopy (EPR) and quenching experiments confirmed the generation of sulfate radical (SO₄•⁻), hydroxyl radical (•OH) and singlet oxygen (¹O₂) in the UV/PMS/20%CNT-TiO₂ system. Almost 100% phenol degradation was observed within 20 min UV-light irradiation. The kinetic reaction rate constant of the UV/PMS/20%CNT-TiO₂ system (0.18 min⁻¹) was 23.7 times higher than that of the PMS/Co₃O₄ system (0.0076 min⁻¹). This higher catalytic performance was ascribed to the introduction of photoinduced electrons, which could enhance the activation of PMS by the transfer of electrons in the UV/PMS/CNT-TiO₂ system.