Suchergebnisse

Ammonia (NH3) emissions and ammonium (NH4+) deposition can have harmful effects on the environment and human health but remain generally unregulated in the U.S. PM2.5 regulations require that an area not exceed an annual average PM2.5 value of 12 μg/m3 (averaged over three years), and since NH3 is a significant precursor to PM2.5 formation these are the closest indirect regulations of NH3 emissions in the U.S. If the U.S. elects to adopt NH3 emission regulations similar to those applied by the European Union, it will be imperative to first adequately quantify NH3 emission sources and transport, and also understand the factors causing varying emissions from each source. To further investigate NH3 emission sources and transport at a regional scale, NH3 was sampled monthly at a subset of nine Ammonia Monitoring Network (AMoN) sites and analyzed for nitrogen isotopic composition of NH3 (δ15N-NH3). The observed δ15N-NH3 values ranged from −42.4 to +7.1‰ with an average of −15.1 ± 9.7. The observed δ15N-NH3 values reported here provide insight into the spatial and temporal trends of the NH3 sources that contribute to ambient [NH3] in the U.S. In regions where agriculture is prevalent (i.e., U.S. Midwest), low and seasonally variable δ15N-NH3 values are observed and are associated with varying agricultural sources. In comparison, rural nonagricultural areas have higher and more seasonally consistent δ15N-NH3 values associated with a constant "natural" (e.g. soil, vegetation, bi-directional flux, ocean) NH3 source. With regards to temporal variation, the peak in U.S. spring agricultural activity (e.g. fertilizer application, livestock waste volatilization) is accompanied by a decrease in δ15N-NH3 values at a majority of the sites, whereas higher δ15N-NH3 values in other seasons could be due to shifting sources (e.g. coal-fired power plants) and/or fractionation scenarios. Fractionation processes that may mask NH3 source signatures are discussed and require further investigation to optimize the utility of the nitrogen isotopic composition to determine NH3 sources and dynamics.

AbstractThose who conduct integrated assessments (IAs) are aware of the need to explicitly consider multiple criteria and uncertainties when evaluating policies for preventing global warming. MCDM methods are potentially useful for understanding tradeoffs and evaluating risks associated with climate policy alternatives. A difficulty facing potential MCDM users is the wide range of different techniques that have been proposed, each with distinct advantages. Methods differ in terms of validity, ease of use, and appropriateness to the problem. Alternative methods also can yield strikingly different rankings of alternatives. A workshop was held in which climate change experts and policy makers evaluated the usefulness of MCDM for IA. Participants applied several methods in the context of a hypothetical greenhouse gas policy decision. Methods compared include value and utility functions, goal programming, ELECTRE, fuzzy sets, stochastic dominance, min max regret, and several weight selection methods. Ranges, rather than point estimates, were provided for some questions to incorporate imprecision regarding weights. Additionally, several visualization methods for both deterministic and uncertain cases were used and evaluated. Analysis of method results and participant feedback through questionnaires and discussion provide the basis for conclusions regarding the use of MCDM methods for climate change policy and IA analyses. Hypotheses are examined concerning predictive and convergent validity of methods, existence of splitting bias among experts, perceived ability of methods to aid decision‐making, and whether expressing imprecision can change ranking results. Because participants gained from viewing a problem from several perspectives and results from different methods often significantly differed, it appears worthwhile to apply several MCDM methods to increase user confidence and insight. The participants themselves recommended such multimethod approaches for policymaking. Yet they preferred the freedom of unaided decision‐making most of all, challenging the MCDM community to create transparent methods that permit maximum user control. Copyright © 2002 John Wiley & Sons, Ltd.