Methane is the most important greenhouse gas after carbon dioxide, with particular influence on near-term climate change. It poses increasing risk in the future from both direct anthropogenic sources and potential rapid release from the Arctic. A range of mitigation (emissions control) technologies have been developed for anthropogenic sources that can be developed for further application, including to Arctic sources. Significant gaps in understanding remain of the mechanisms, magnitude, and likelihood of rapid methane release from the Arctic. Methane may be released by several pathways, including lakes, wetlands, and oceans, and may be either uniform over large areas or concentrated in patches. Across Arctic sources, bubbles originating in the sediment are the most important mechanism for methane to reach the atmosphere. Most known technologies operate on confined gas streams of 0.1% methane or more, and may be applicable to limited Arctic sources where methane is concentrated in pockets. However, some mitigation strategies developed for rice paddies and agricultural soils are promising for Arctic wetlands and thawing permafrost. Other mitigation strategies specific to the Arctic have been proposed but have yet to be studied. Overall, we identify four avenues of research and development that can serve the dual purposes of addressing current methane sources and potential Arctic sources: (1) methane release detection and quantification, (2) mitigation units for small and remote methane streams, (3) mitigation methods for dilute (<1000 ppm) methane streams, and (4) understanding methanotroph and methanogen ecology.

An experimental study of hetero-and homogeneous mercury oxidation chemistry was conducted in a bench-scale flame-based flow reactor with a residence time of 2.9 s. Homogeneous mercury oxidation levels increased with an increasing HCl concentration, with oxidation increasing to 29% at HCl concentrations of 555 parts per million by volume (ppmv). The presence of SO 2 alone also led to Hg oxidation, with approximately 20% oxidation observed at SO 2 concentrations ranging from 100 to 900 ppmv. When both HCl and SO 2 were present, mercury oxidation was enhanced in the presence of SO 2 when the concentration of HCl was 200 ppmv and inhibited when concentration of HCl was 555 ppmv. To examine heterogeneous effects, iron oxide or montmorillonite particles were injected into the post-flame gases of the system. Mercury oxidation by HCl was enhanced at high iron oxide particle concentrations (>100 m α-Fe 2 O 3 2 /m 3 of flue gas) compared to the homogeneous system. When iron oxide particles were injected in the presence of 100À400 ppmv SO 2 without HCl, mercury oxidation was enhanced at particle loadings less than or equal to 1 m α-Fe 2 O 3 2 /m 3 of flue gas and decreased with an increasing particle loading. At a SO 2 concentration of 500 ppmv, mercury oxidation increased with an increasing particle concentration. Without HCl or SO 2 in the system, mercury oxidation in the presence of iron oxide particles alone was found to be negligible. To determine if the increased oxidation by HCl or SO 2 occurred solely because of an increased surface area, montmorillonite particles were injected, and under these conditions, no increase in the extent of mercury oxidation was observed, suggesting that iron oxide particle surfaces are an important contributor to the promotion of mercury oxidation in coal combustion systems.

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The overall goal of this project was to produce a working dynamic model to predict the transformation and partitioning of trace metals resulting from combustion of a broad range of fuels. The information provided from this model will be instrumental in efforts to identify fuels and conditions that can be varied to reduce metal emissions. Through the course of this project, it was determined that mercury (Hg) and arsenic (As) would be the focus of the experimental investigation. Experiments were therefore conducted to examine homogeneous and heterogeneous mercury oxidation pathways, and to assess potential interactions between arsenic and calcium. As described in this report, results indicated that the role of SO 2 on Hg oxidation was complex and depended upon overall gas phase chemistry, that iron oxide (hematite) particles contributed directly to heterogeneous Hg oxidation, and that As-Ca interactions occurred through both gas-solid and within-char reaction pathways. Modeling based on this study indicated that, depending upon coal type and fly ash particle size, vaporization-condensation, vaporization-surface reaction, and As-CaO in-char reaction all play a role in arsenic transformations under combustion conditions.

Hail and Farewell.-When those who go abroad to study in libraries get to England once more, they will miss the two most familiar faces. At Oxford, Falconer Madan is no longer Bodley's Librarian, and at the British Museum Mr. Barwick has been suc