Midpoints versus endpoints: The sacrifices and benefits

On May 25–26, 2000 in Brighton (England), the third in a series of international workshops was held under the umbrella of UNEP addressing issues in Life Cycle Impact Assessment (LCIA). The workshop provided a forum for experts to discuss midpoint vs. endpoint modeling. Midpoints are considered to be links in the cause-effect chain (environmental mechanism) of an impact category, prior to the endpoints, at which characterization factors or indicators can be derived to reflect the relative importance of emissions or extractions. Common examples of midpoint characterization factors include ozone depletion potentials, global warming potentials, and photochemical ozone (smog) creation potentials. Recently, however, some methodologies have adopted characterization factors at an endpoint level in the cause-effect chain for all categories of impact (e.g., human health impacts in terms of disability adjusted life years for carcinogenicity, climate change, ozone depletion, photochemical ozone creation; or impacts in terms of changes in biodiversity, etc.). The topics addressed at this workshop included the implications of midpoint versus endpoint indicators with respect to uncertainty (parameter, model and scenario), transparency and the ability to subsequently resolve trade-offs across impact categories using weighting techniques. The workshop closed with a consensus that both midpoint and endpoint methodologies provide useful information to the decision maker, prompting the call for tools that include both in a consistent framework.     

Airspace Surface Chemistry Mediates O3-Induced Lung Injury

Ozone (O₃) produces diverse pulmonary pathophysiologies but with marked heterogeneities relative to species, age, anatomic site, disease, and exposure history. These pronounced susceptibility variations have remained largely undefined. We have postulated that interactions between inhaled O₃ and the airspace surfaces appreciably govern the distribution and extent of lung injury. O₃ displays unique absorption properties wherein chemical reaction with the epithelial lining fluid (ELF) maintains the net flux from the gas phase and couples O₃ uptake with the generation of products that lead to cell injury. Diversities in respiratory tract geometry and interfacial physicochemical conditions leads to spatially heterogeneous rates of O₃ flux into the ELF which combine with the local production of bioactive species to dictate the local dose. We have observed that both the uptake and distribution of acute epithelial injury is principally localized to the conducting airways. O₃ preferentially reacts with ELF ascorbic (AH₂) and uric acids (UA) although reaction with GSH and unsaturated fatty acids (UFA) occur to a lesser extent. UFA reactions may not generate sufficient bioactive materials to account for acute cell injury. Reactions with AH₂ and GSH, but not UA or Trolox, form secondary oxidants that initiate oxidation of model membranes and in vitro cell damage. However, secondary oxidant production is antioxidant concentration-dependent with a hyperbolic-shaped dose/response curve. Acquisition of species-specific data characterizing the pharmacodynamics of ELF substrate turnover under both basal and exposure conditions are critical to further our understanding of how surface chemistry regulates the balance between quenching of inhaled O₃ and conditions that promote production of bioactive/cytotoxic species and, therefore, biological outcomes.     

Life cycle assessment of electrical and thermal energy systems for commercial buildings

Background, Aim and Scope The objective of this life cycle assessment (LCA) study is to develop LCA models for energy systems in order to assess the potential environmental impacts that might result from meeting energy demands in buildings. The scope of the study includes LCA models of the average electricity generation mix in the USA, a natural gas combined cycle (NGCC) power plant, a solid oxide fuel cell (SOFC) cogeneration system; a microturbine (MT) cogeneration system; an internal combustion engine (ICE) cogeneration system; and a gas boiler. Methods LCA is used to model energy systems and obtain the life cycle environmental indicators that might result when these systems are used to generate a unit energy output. The intended use of the LCA analysis is to investigate the operational characteristics of these systems while considering their potential environmental impacts to improve building design using a mixed integer linear programming (MILP) optimization model. Results The environmental impact categories chosen to assess the performance of the energy systems are global warming potential (GWP), acidification potential (AP), tropospheric ozone precursor potential (TOPP), and primary energy consumption (PE). These factors are obtained for the average electricity generation mix, the NGCC, the gas boiler, as well as for the cogeneration systems at different part load operation. The contribution of the major emissions to the emission factors is discussed. Discussion The analysis of the life cycle impact categories indicates that the electrical to thermal energy production ratio has a direct influence on the value of the life cycle PE consumption factors. Energy systems with high electrical to thermal ratios (such as the SOFC cogeneration systems and the NGCC power plant) have low PE consumption factors, whereas those with low electrical to thermal ratios (such as the MT cogeneration system) have high PE consumption factors. In the case of GWP, the values of the life cycle GWP obtained from the energy systems do not only depend on the efficiencies of the systems but also on the origins of emissions contributing to GWP. When evaluating the life cycle AP and TOPP, the types of fuel as well as the combustion characteristics of the energy systems are the main factors that influence the values of AP and TOPP. Conclusions An LCA study is performed to eraluate the life cycle emission factors of energy systems that can be used to meet the energy demand of buildings. Cogeneration systems produce utilizable thermal energy when used to meet a certain electrical demand which can make them an attractive alternative to conventional systems. The life cycle GWP, AP, TOPP and PE consumption factors are obtained for utility systems as well as cogeneration systems at different part load operation levels for the production of one kWh of energy output. Recommendations and Perspectives Although the emission factors vary for the different energy systems, they are not the only factors that influence the selection of the optimal system for building operations. The total efficiencies of the system play a significant part in the selection of the desirable technology. Other factors, such as the demand characteristics of a particular building, influence the selection of energy systems. The emission factors obtained from this LCA study are used as coefficients of decision variables in the formulation of an MILP to optimize the selection of energy systems based on environmental criteria by taking into consideration the system efficiencies, emission characteristics, part load operation, and building energy demands. Therefore, the emission factors should not be regarded as the only criteria for choosing the technology that could result in lower environmental impacts, but rather one of several factors that determine the selection of the optimum energy system. ESS-Submission Editor: Arpad Horvath (horvath@ce.berkeley.edu)     

Modulation of age‐related changes in oxidative stress markers and energy status in the rat heart and hippocampus: a significant role for ozone therapy

Oxidative stress emerges as a key player in the ageing process. Controlled ozone administration is known to promote an oxidative preconditioning or adaptation to oxidative stress. The present study investigated whether prophylactic ozone administration could interfere with the age‐related changes in the heart and the hippocampus of rats. Four groups of rats, aged about 3 months old, were used. Group 1 (Prophylactic ozone group) received ozone/oxygen mixture by rectal insufflations (0.6 mg/kg) twice/week for the first 3 months, then once/week till the age of 15 months. Group 2 (Oxygen group) received oxygen as vehicle for ozone in a manner similar to group 1. Group 3 (Aged control group) was kept without any treatment until the age of 15 months. A fourth group of rats (Adult control group) was evaluated at 3 months of age to provide baseline data. Ozone alleviated age‐associated redox state imbalance as evidenced by reduction of lipid and protein oxidation markers, lessening of lipofuscin deposition, restoration of glutathione levels in both tissues and normalization of glutathione peroxidase activity in the heart tissue. Ozone also mitigated age‐associated energy failure in the heart and the hippocampus, improved cardiac cytosolic Ca²⁺ homeostasis and restored the attenuated Na⁺, K⁺‐ATPase activity in the hippocampus of aged rats. These data provide new evidence concerning the anti‐ageing potential of prophylactic ozone administration. Copyright © 2012 John Wiley & Sons, Ltd.     

Enzymatic determination of ascorbic acid in leaf cell walls using acidic buffer during infiltration

A modification of the procedure of extraction of cell wall solution for enzymatic determination of ascorbic acid and its reduction level in the apoplast of leaf cells is proposed. The modification consists in infiltration of leaves with citric acid/sodium phosphate buffer, pH 3, instead of customarily used neutral solutions. In acidic media autooxidation of ascorbic acid is effectively suppressed, so that infiltration could be performed at laboratory temperatures. Using polyacrylamide gel electrophoresis and infiltration solutions of pH down to 1.5 it is shown, that at pH 3 the extracted fluid is not contaminated with intracellular substances if appropriate vacuum and centrifugation forces are used. The modification is shown to be more effective for leaves ofPhaseolus than for those ofSpinacia. In cell walls of mature leaves of these species the concentration of ascorbic acid was found to be around 1 mM, with reduction level up to 0.90. The role of ascorbic acid in cell walls as ozone scavenger is discussed This work has been supported by grant No. 287 from the Estonian Science Foundation. We are grateful to Martin Gibbs from the American Society of Plant Physiologists for his kind gift of AA, AAO and DTT. We are also indebted to Vello Jaaska from the Institute of Zoology and Botany of the Estonian Academy of Sciences for performing PAGE analyses.