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Particulate matter (PM) emitted from fossil fuel-fired units can be classified as either filterable or condensible PM. Condensible PM typically is not measured because federal and most state regulations do not require sources to do so. To determine the magnitude of condensible PM emissions relative to filterable PM emissions and to better understand condensible PM measurement issues, a review and analysis of actual U.S. Environmental Protection Agency (EPA) Method 202 (for in-stack condensible PM 10 ) and EPA Method 201/201A (for in-stack filterable PM 10 ) results were conducted. Methods 202 and 201/201A results for several coal-burning boilers showed that the condensible PM, on average, comprises approximately three-fourths (76%) of the total PM 10 stack emissions. Methods 202 and 201/201A results for oil-and natural gas-fired boilers showed that the condensible PM, on average, comprises 50% of the total PM 10 stack emissions. Methods 202 and 201/201A results for oil-, natural gas-, and kerosene-fired combustion turbines showed that the condensible PM, on average, comprises 69% of the total PM 10 stack emissions. Based on these limited measurements, condensible PM can make a significant contribution to total PM 10 emissions for fossil fuel-fired units. A IMPLICATIONS This study examines issues associated with the measurement of a form of PM, condensible PM, that is not routinely accounted for in assessing compliance with PM emission limits. The data analyzed in this study show that condensible PM constitutes a significant fraction of total PM 10 emissions for fossil fuel-fired units, although there is some controversy associated with the in-stack measurement methodology, EPA Method 202. The accounting of condensible PM for existing units could prompt permit re-openings and PM 10 emission limit revisions. For some sources, both existing and new, demonstrating compliance with PM air quality standards could be difficult.

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Maryland will impose restrictions on poultry litter application to soils with excessive P by the year 2005. Alternative uses for poultry litter are being considered, including burning as a fuel to generate electricity. The resulting ash contains high levels of total P, but the availability for crop uptake has not been reported. Our objective was to compare the effectiveness of poultry litter ash (PLA) and potassium phosphate (KP) as a P source for wheat (Triticum aestivum L.) in acidic soils, without and with limestone application. Two acidic soils (pH 4.25 and 4.48) were studied, unlimed or limed to pH 6.5 before cropping. The PLA and KP were applied at 0, 39, and 78 kg P ha(-1), after which wheat was grown. Limestone significantly increased wheat yield, but the P sources without limestone did not. The two P sources were not significantly different as P fertilizer. At the 78 kg P ha(-1) rate, wheat shoot-P concentrations were 1.10 and 1.12 g kg(-1) for the PLA treatment compared with 0.90 and 0.89 g kg(-1) for KP in the nonlimed and limed soils, respectively. Trace element concentrations in wheat shoots from the PLA treatment were less than or equal to KP and the control. The low levels of water-soluble P and metals in the soils and the low metal concentrations in wheat suggest that PLA is an effective P fertilizer. Further studies are needed to determine the optimum application rate of PLA as a P fertilizer.

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Coal-fired power plants in the United States are required to reduce their emissions of mercury (Hg) into the atmosphere to lower the exposure of Hg to humans. The effectiveness of power-plant emission controls on the atmospheric concentrations of Hg in the United States is largely unknown because there are few long-term high-quality atmospheric Hg data sets. Here, we present the atmospheric concentrations of Hg and sulfur dioxide (SO2) measured from 2006 to 2015 at a relatively pristine location in western Maryland that is several (>50 km) kilometers downwind of power plants in Ohio, Pennsylvania, and West Virginia. Annual average atmospheric concentrations of gaseous oxidized mercury (GOM), SO2, fine particulate mercury (PBM2.5), and gaseous elemental mercury (GEM) declined by 75%, 75%, 43%, and 13%, respectively, and were strongly correlated with power-plant Hg emissions from the upwind states. These results provide compelling evidence that reductions in Hg emissions from power plants in the United States had their intended impact to reduce regional Hg pollution.

The techniques of pulse radiolysis and emission spectroscopy have been used to determine absolute total emission yields for the XeBr* exciplex. By application of known formation and quenching rate constants and mechanisms, individual fluorescence yields have been determined for the unquenched three-body ionic recombination reaction, Xe 2 + + Br -+ Xe f XeBr* + 2Xe, G o + ) 3.40 ( 0.18, and for the reaction of electronically excited xenon atoms with CF 3 Br, Xe* + CF 3 Br f XeBr* + CF 3 , G o * ) 0.68 ( 0.10. These experimental yields are compared to the predictions of current theoretical models, which allow calculation of the efficiency for each ion-pair recombination event and excited state reaction to give the fluorescent XeBr* exciplex as 75% and 36%, respectively.

24 32 ' ' 6 Figure 6. Adsorption of ENTMP on calcium fluoride crystals at equilibrium. Plots of r against [ENTMP].uration g = 0.4, 0.2, and 0.1 respectively. These values reflect the high adsorption affinity at low relative undersaturation in the presence of ENTMP. A similar dependence of the degree of inhibition with change in driving force has been observed for the influence of phosphonate on the dissolution rate of magnesium fluoride" and barium fluoride19 in aqueous solution. As noted 8 io ,~N T M P J mol c1 for the crystallization of gypsum by Van Rosmalen and coworkers,m the effectiveness of the HEDP as an inhibitor depends on the degree of supersaturation.In order to investigate the adsorption of phosphonate on the calcium fluoride crystals surface, adsorption equilibrium experiments were made for ENTMP on calcium fluoride crystals at u = 0. A typical adsorption isotherm is plotted in Figure 6. Assuming that the area occupied by an ENTMP molecule is 50 X m2, the fraction of the solid surface covered by adsorption molecules is only 6% at the plateau in Figure 6. At this ENTMP concentration, the dissolution rate is reduced by more than 92%. Adsorption affinity constant at equilibrium 5.2 X lo5 dm3 mol-' is in satisfactory agreement with the kinetic adsorption affinity constants los dm3 mol-'. The dissolution rate of magnesium fluoride was reduced by more than 80% when only 9% of the crystal surface was covered by HEDP molecule^.^' Moreover, the rate of crystallization may be reduced virtually to zero when only 5-7% of the crystal surface was covered by adsorbed inhibitor moIecules.2',22The emission spectroscopy/pulse radiolysis method of determining three-body ionic recombination rate constants in raregas-halogen source gas mixtures has been extended to systems where the emission is produced by both ionic and nonionic pathways. This has enabled recombination coefficient measurements to be done over a large pressure range for irradiated Kr/SF, and Xe/CFC13 gas mixtures. The rate constants measured for both these systems show the typical pressure dependence of an increase to a maximum value of -2.5 X IOl5 M-l s-l (-4 X IOd cm3 d), before the onset of the diffusion-controlled reaction. These values have been compared to the predictions of the Langevin-Harper diffusion-controlled and the Bates termolecular recombination models. The large discrepancies between theory and experiment have shown that other recombination processes dominate the ionic recombination.