Particulate matter (PM) emissions from stationary combustion sources burning coal, fuel oil, biomass, and waste, and PM from internal combustion (IC) engines burning gasoline and diesel, are a significant source of primary particles smaller than 2.5 µm (PM 2.5 ) in urban areas. Combustion-generated particles are generally smaller than geologically produced dust and have unique chemical composition and morphology. The fundamental processes affecting formation of combustion PM and the emission characteristics of important applications are reviewed. Particles containing transition metals, ultrafine particles, and soot are emphasized because these types of particles have been studied extensively, and their emissions are controlled by the fuel composition and the oxidant-temperature-mixing history from the flame to the stack. There is a need for better integration of the combustion, air pollution control, atmospheric chemistry, and inhalation health research communities. Epidemiology has demonstrated that susceptible individuals are being harmed by ambient PM. Particle surface area, number of ultrafine particles, bioavailable transition metals, polycyclic aromatic hydrocarbons (PAH), and other particle-bound organic compounds are suspected to be more important than particle mass in determining the effects of air pollution. Time-and size-resolved PM measurements are needed for testing mechanistic toxicological hypotheses, for characterizing the relationship between combustion operating conditions and transient emissions, and for source apportionment studies to develop air quality plans. Citations are provided to more specialized reviews, and the concluding comments make suggestions for further research.

Emission measurements were obtained for a variety of military vehicles at Hill Air Force Base (Ogden, UT) in November 2000 as part of a Strategic Environmental Research and Development Program. Aircraft ground support equipment vehicles using gasoline, diesel, and JP8 fuels were tested using chassis dynamometers under predetermined load. The exhaust from the tested vehicle was passed to a dilution tunnel where it was diluted 30-40 times and collected using Micro-Orifice Uniform Deposit Impactor (MOUDI) fitted with aluminum substrates, an XAD-coated annular denuder, and a filter followed by a solid adsorbent. All MOUDI substrates were analyzed for mass and for organic and elemental (EC) carbon by the thermal/optical reflectance method and for polycyclic aromatic hydrocarbons (PAHs) by GC/MS. Black carbon was measured with a photoacoustic instrument. The denuder and filter/solid adsorbent samples were analyzed for semivolatile PAH. Overall, there is more mass and higher EC contribution when the vehicle is run under higher load in comparison with the low load. However, older vehicles generally show more mass and EC emissions than newer vehicles, and there is a shift toward smaller particle sizes for the low load, which is most pronounced for newer vehicles. The particle-associated semivolatile PAHs and nonvolatile four-through six-ring PAHs are present predominantly on the submicron particles collected on MOUDI stages 0.1-0.18, 0.18-0.32, and 0.32-0.56 microm. For the low-load runs, the distribution of PAHs seems to be shifted toward smaller size particles. The gas-particle phase distribution of semivolatile PAHs depends also on the engine loading. For idle, not only are the more volatile two- and three-ring PAHs, from naphthalene to dimethylphenanthrenes, retained on the denuder portion, but also less volatile four-ring PAHs, such as fluoranthene and pyrene, are retained by the denuder at the 80-90% range, which implies that they are present predominantly in the gas phase. In contrast, for engines under high loads, a much larger portion of three- and four-ring PAHs are partitioned to the particle phase.

Résumé -Boucle chimique pour la combustion du charbon avec un transporteur d'oxygène à base d'oxyde de cuivre -Une analyse préliminaire a été conduite pour estimer les performances d'un procédé en boucle chimique découplé (CLOU, chemical looping uncoupling) pour la combustion du charbon avec un transporteur d'oxygène à base d'oxyde de cuivre. Les avantages de ce système sont démontrés en établissant le bilan énergétique, l'inventaire et le débit de circulation du matériau transportant l'oxygène, les taux de conversion du carbone et la pression partielle en oxygène dans le réacteur de combustion. Pour faire cette analyse, des données expérimentales de cyclage CuO/Cu 2 O ont été utilisées afin de déterminer les cinétiques de décomposition et d'oxydation du matériau. Elles ont été obtenues avec un oxyde non supporté. La cinétique de décomposition est très rapide à 950°C dans les conditions du réacteur de combustion. Il est montré que la cinétique d'oxydation est maximale au voisinage de 800°C, la vitesse décroissant ensuite pour des températures plus élevées, à cause de résistances diffusionnelles liées à la formation d'une couche de CuO entourant le Cu 2 O. L'analyse montre que le CLOU permet une combustion rapide du carbone, les temps de combustion du carbone étant plus lents que les temps de décomposition du transporteur d'oxygène. Pour confirmer le potentiel du procédé, des données cinétiques additionnelles sont nécessaires sur des oxydes supportés à haute température (>850°C), dans les conditions du réacteur de combustion permettant la libération d'oxygène par l'oxyde de cuivre. Abstract -Chemical Looping with Copper Oxide as Carrier and Coal as Fuel -A preliminary analysis has been conducted of the performance of a Chemical Looping system with Oxygen Uncoupling (CLOU) with copper oxide as the oxygen carrier and coal approximated by carbon as the fuel. The advantages of oxygen uncoupling are demonstrated by providing the energy balances

Particulate air pollution contains iron, and some of the pathological effects after inhalation may be due to radical species produced by iron-catalyzed reactions. We tested the hypothesis that iron present in coal fly ash (CFA) could induce the expression and synthesis of the inflammatory cytokine interleukin-8 (IL-8). CFA, containing as much as 14% iron, was used as a model combustion source particle. Three coal types were used to generate three size fractions enriched in particles [submicron (<1 micrometer), fine (<2.5 micrometer), or coarse (2.5-10 micrometer]), as well as the fraction of >10 micrometer. Treatment of human lung epithelial (A549) cells for 4 h with CFA from Utah enriched in <1 micrometer particles (20 microgram/cm(2)) resulted in a 2.6-fold increase in mRNA levels for IL-8. IL-8 levels were increased in the medium by as much as 8-fold when cells were treated with the fraction enriched in the smallest size Utah CFA for 24 h. IL-8 production was completely inhibited when the CFA was pretreated with the metal chelator desferrioxamine B, suggesting that a transition metal was responsible for the induction, probably iron. Treatment with a soluble form of iron, ferric ammonium citrate (FAC), mimicked the IL-8 level increase observed with CFA. There was a direct relationship, above a threshold level of bioavailable iron, between the levels of IL-8 and bioavailable iron in A549 cells treated with CFA or FAC. Further, the relationship between IL-8 and bioavailable iron for CFA was indistinguishable from that for FAC. These results strongly suggest that iron can induce IL-8 in A549 cells and that iron was the likely component of CFA that induced IL-8. CFA-induced IL-8 production was inhibited by tetramethylthiourea or dimethyl sulfoxide, suggesting that radical species were involved in the induction. These results demonstrate that iron present in CFA may be responsible for production and release of inflammatory mediators by the lung epithelium through generation of radical species and suggest that iron may contribute to the exacerbation of respiratory problems by particulate air pollution.

Oxidation kinetics and fringe analysis studies of three "model" carbons, ranging from fullerenic to onion-like nanostructures and a reference diesel soot were performed in a thermogravimetric analyzer. The samples were oxidized isothermally at temperatures ranging from 575 to 775 °C in air. Multiple tests were performed to obtain the most favorable operating conditions to minimize mass-transfer diffusion limitations in the experiments. First-order reaction kinetics and an Arrhenius-type equation were used to extract the rate constants at each temperature. The activation energies for the oxidation of the carbon samples ranges from 124 to 204 kJ/mol, and it was approximately 140 kJ/mol for the reference diesel soot sample. The onion-like structure exhibited a slower kinetic rate compared to the other carbons. Similar kinetic parameters were found for "intermediate structure" model carbon and reference diesel soot. Fringe analysis explained the differences in the kinetic parameters between carbon samples studied. The onion-like carbon "nascent" sample had a broader range of lamellae length with smaller tortuosity distribution, suggesting stacking; the "nascent" fullerenic carbon had much shorter mean lamella length distribution and broader tortuosity, suggesting more curvature. Nanostructure metrics of the reference diesel soot and intermediate model carbon were between the other two carbons. Results confirm a structure-property relationship between oxidative reactivity with carbon nanostructure.

Aerosol particulates are generated by coal combustion. The amount and properties of aerosol particulates, specifically size distribution and composition, can be affected by combustion conditions. Understanding the formation of these particles is important for predicting emissions and understanding potential deposition. Oxy-fuel combustion conditions utilize an oxygen-enriched gas environment with CO(2). The high concentration of CO(2) is a result of recycle flue gas which is used to maintain temperature. A hypothesis is that high CO(2) concentration reduces the vaporization of refractory oxides from combustion. A high-temperature drop-tube furnace was used under different oxygen concentrations and CO(2) versus N(2) to study the effects of furnace temperature, coal type, and gas phase conditions on particulate formation. A scanning mobility particle sizer (SMPS) and aerodynamic particle sizer (APS) were utilized for particle size distributions ranging from 14.3 nm to 20 μm. In addition, particles were collected on a Berner low pressure impactor (BLPI) for elemental analysis using scanning electron microscopy and energy dispersive spectroscopy. Three particle size modes were seen: ultrafine (below 0.1 μm), fine (0.1 to 1.0 μm), and coarse (above 1 μm). Ultrafine mass concentrations were directly related to estimated particle temperature, increasing with increasing temperature. For high silicon and calcium coals, Utah Skyline and PRB, there was a secondary effect due to CO(2) and the hypothesized reaction. Illinois #6, a high sulfur coal, had the highest amount of ultrafine mass and most of the sulfur was concentrated in the ultrafine and fine modes. Fine and coarse mode mass concentrations did not show a temperature or CO(2) relationship. (The table of contents graphic and abstract graphic are adapted from ref 27.).

Chemical-looping with oxygen uncoupling (CLOU) offers a promise to reduce energy penalty by facilitating the capture of CO2 emitted from power plants. It has a potential to lower the oxygen carrier inventory of the fuel reactor in contrast to chemical-looping combustion (CLC). The primary mechanism in CLOU for the combustion of solid fuels is their reaction with gaseous oxygen released by the decomposition of a metal oxide, which differs from CLC of solid fuels where the solid fuel has to be gasified first. The slower gasification reaction in CLC is subsequently followed by combustion of the fuel with a circulating oxygen carrier. The present study is concerned with the rate analysis from reported batch fluidized bed CLOU experimental data of Mexican petcoke particles by a CuO/ZrO2 oxygen carrier. The methodology to determine the kinetic parameters for CuO decomposition and solid fuel oxidation during the fuel reactor stage and for Cu2O oxidation in the air reactor stage have been discussed. The results of the study are expected to help in the development of a process model for CLOU, furthering the development of a pilot scale process.

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