Characterization of Fine Particulate Matter Produced by Combustion of Residual Fuel Oil

ABSTRACT

Combustion experiments were carried out on four different residual fuel oils in a 732-kW boiler. PM emission samples were separated aerodynamically by a cyclone into fractions that were nominally less than and greater than 2.5 |j.m in diameter. However, examination of several of the samples by computer-controlled scanning electron microscopy (CCSEM) revealed that part of the PM_2.5 fraction consists of carbonaceous cenospheres and vesicular particles that range up to 10 |j.m in diameter. X-ray absorption fine structure (XAFS) spectroscopy data were obtained at the S, V, Ni, Fe, Cu, Zn, and As K-edges and at the Pb L-edge. Deconvolution of the X-ray absorption near edge structure (XANES) region of the S spectra established that the dominant molecular forms of S present were sulfate (26-84% of total S) and thiophene (13-39% of total S). Sulfate was greater in the PM_2.5 samples than in the PM₂₅₊ samples. Inorganic sulfides and elemental sulfur were present in lower percentages. The Ni XANES spectra from all of the samples agreed fairly well with that of NiSO₄, while most of the V spectra closely resembled that of vanadyl sulfate (VO?SO₄?xH₂O). The other metals investigated (i.e., Fe, Cu, Zn, and Pb) also were present predominantly as sulfates. Arsenic was present as an arsen-ate (As⁺⁵). X-ray diffraction patterns of the PM_2.5 fraction exhibit sharp lines due to sulfate compounds (Zn, V, Ni, Ca, etc.) superimposed on broad peaks due to amorphous carbons. All of the samples contain a significant organic component, with the loss on ignition (LOI) ranging from 64 to 87% for the PM_2.5 fraction and from 88 to 97% for the PM_2.5+ fraction. Based on ¹³C nuclear magnetic resonance (NMR) analysis, the carbon is predominantly condensed in graphitic structures. Aliphatic structure was detected in only one of seven samples examined.     

Development of Emission Factors for Polycarbonate Processing

Abstract

Emission factors for selected volatile organic compounds (VOCs) and particulate emissions were developed while processing eight commercial grades of polycarbonate (PC) and one grade of a PC/acrylonitrile-butadiene-styrene (ABS) blend. A small commercial-type extruder was used, and the extrusion temperature was held constant at 304 °C. An emission factor was calculated for each substance measured and is reported as pounds released to the atmosphere/million pounds of polymer resin processed [ppm (wt/wt)]. Scaled to production volumes, these emission factors can be used by processors to estimate emission quantities from similar PC processing operations.     

Validation of Three New Methods for Determination of Metal Emissions Using a Modified Environmental Protection Agency Method 301

Abstract

Three new methods applicable to the determination of hazardous metal concentrations in stationary source emissions were developed and evaluated for use in U.S. Environmental Protection Agency (EPA) compliance applications. Two of the three independent methods, a continuous emissions monitor-based method (Xact) and an X-ray-based filter method (XFM), are used to measure metal emissions. The third method involves a quantitative aerosol generator (QAG), which produces a reference aerosol used to evaluate the measurement methods. A modification of EPA Method 301 was used to validate the three methods for As, Cd, Cr, Pb, and Hg, representing three hazardous waste combustor Maximum Achievable Control Technology (MACT) metal categories (low volatile, semivolatile, and volatile). The modified procedure tested the methods using more stringent criteria than EPA Method 301; these criteria included accuracy, precision, and linearity. The aerosol generation method was evaluated in the laboratory by comparing actual with theoretical aerosol concentrations. The measurement methods were evaluated at a hazardous waste combustor (HWC) by comparing measured with reference aerosol concentrations. The QAG, Xact, and XFM met the modified Method 301 validation criteria. All three of the methods demonstrated precisions and accuracies on the order of 5%. In addition, correlation coefficients for each method were on the order of 0.99, confirming the methods’ linear response and high precision over a wide range of concentrations. The measurement methods should be applicable to emissions from a wide range of sources, and the reference aerosol generator should be applicable to additional analytes. EPA recently approved an alternative monitoring petition for an HWC at Eli Lilly’s Tippecanoe site in Lafayette, IN, in which the Xact is used for demonstrating compliance with the HWC MACT metal emissions (low volatile, semivolatile, and volatile). The QAG reference aerosol generator was approved as a method for providing a quantitative reference aerosol, which is required for certification and continuing quality assurance of the Xact.     

The Steubenville Comprehensive Air Monitoring Program (SCAMP): Overview and Statistical Considerations

Abstract

Average concentrations of particulate matter with an aerodynamic diameter less than or equal to 2.5 μm (PM_2.5) in Steubenville, OH, have decreased by more than 10 μg/m³ since the landmark Harvard Six Cities Study¹ associated the city’s elevated PM_2.5 concentrations with adverse health effects in the 1980s. Given the promulgation of a new National Ambient Air Quality Standard (NAAQS) for PM_2.5 in 1997, a current assessment of PM_2.5 in the Steubenville region is warranted. The Steubenville Comprehensive Air Monitoring Program (SCAMP) was conducted from 2000 through 2002 to provide such an assessment. The program included both an outdoor ambient air monitoring component and an indoor and personal air sampling component. This paper, which is the first in a series of four that will present results from the outdoor portion of SCAMP, provides an overview of the outdoor ambient air monitoring program and addresses statistical issues, most notably autocorrelation, that have been overlooked by many PM_2.5 data analyses. The average PM_2.5 concentration measured in Steubenville during SCAMP (18.4 μg/m³) was 3.4g/m³ above the annual PM_2.5 NAAQS. On average, sulfate and organic material accounted for ～31% and 25%, respectively, of the total PM_2.5 mass. Local sources contributed an estimated 4.6 μg/m³ to Steubenville’s mean PM_2.5 concentration. PM_2.5 and each of its major ionic components were significantly correlated in space across all pairs of monitoring sites in the region, suggesting the influence of meteorology and long-range transport on regional PM_2.5 concentrations. Statistically significant autocorrelation was observed among time series of PM_2.5 and component data collected at daily and 1-in-4-day frequencies during SCAMP. Results of spatial analyses that accounted for autocorrelation were generally consistent with findings from previous studies that did not consider autocorrelation; however, these analyses also indicated that failure to account for autocorrelation can lead to incorrect conclusions about statistical significance.     

Ozone and Other Air Quality-Related Variables Affecting Visibility in the Southeast United States

Abstract

An analysis of ozone (O₃) concentrations and several other air quality-related variables was performed to elucidate their relationship with visibility at five urban and semi-urban locations in the southeast United States during the summer seasons of 1980-1996. The role and impact of O₃ on aerosols was investigated to ascertain a relationship with visibility. Regional trend analysis over the 1980s reveals an increase in maximum O₃ concentration coupled with a decrease in visibility. However, a similar analysis for the 1990s shows a leveling-off of both O₃ and visibility; in both cases, the results were not statistically significant at the 5% level. A case study of site-specific trends at Nashville, TN, followed similar trends. To better understand the relationships between O₃ concentration and visibility, the analysis was varied from yearly through daily to hourly averaged values. This increased temporal resolution showed a statistically significant inverse relationship between visibility and O₃. Site-specific hourly r² values ranged from 0.02 to 0.43. Additionally, by performing back-trajectory analysis, it was found that the visibility degraded by air mass migration over polluted areas.     

Minimax Regret Analysis for Municipal Solid Waste Management: An Interval-Stochastic Programming Approach

Abstract

In this study, an interval minimax regret programming (IMMRP) method is developed for the planning of municipal solid waste (MSW) management under uncertainty. It improves on the existing interval programming and minimax regret analysis methods by allowing uncertainties presented as both intervals and random variables to be effectively communicated into the optimization process. The IMMRP can account for economic consequences under all possible scenarios without any assumption on their probabilities. The developed method is applied to a case study of long-term MSW management planning under uncertainty. Multiple scenarios associated with different cost and risk levels are analyzed. Reasonable solutions are generated, demonstrating complex tradeoffs among system cost, regret level, and system-failure risk. The method can also facilitate examination of the difference between the cost incurred with identified strategy and the least cost under an ideal condition. The results can help determine desired plans and policies for waste management under a variety of uncertainties.     

Near-source air quality impacts of large olefin flares

Large petrochemical flares, common in the Houston Ship Channel (the Ship Channel) and other industrialized areas in the Gulf of Mexico region, emit hundreds to thousands of pounds per hour of highly reactive volatile organic compounds (HRVOCs). We employed fine horizontal resolution (200 m?×?200 m) in a three-dimensional (3D) Eulerian chemical transport model to simulate two historical Ship Channel flares. The model reasonably reproduced the observed ozone rise at the nearest monitoring stations downwind of the flares. The larger of the two flares had an olefin emission rate exceeding 1400 lb/hr. In this case, the model simulated a rate of increase in peak ozone greater than 40 ppb/hr over a 12 km?×?12 km horizontal domain without any unusual meteorological conditions. In this larger flare, formaldehyde emissions typically neglected in official inventories enhanced peak ozone by as much as 16 ppb and contributed over 10 ppb to ambient formaldehyde up to ～8 km downwind of the flare. The intense horizontal gradients in large flare plumes cannot be simulated by coarse models typically used to demonstrate ozone attainment. Moreover, even the relatively dense monitoring network in the Ship Channel may not be able to detect many transient high ozone events (THOEs) caused by industrial flare emissions in the absence of stagnant air recirculation or stalled sea breeze fronts, even though such conditions are unnecessary for the occurrence of THOEs.

Implications: Flare minimization may be an important strategy to attain the U.S. federal ozone standard in industrialized areas, and to avoid inordinate exposure to formaldehyde in neighborhoods surrounding petrochemical facilities. Moreover, air quality monitoring networks, emission inventories, and chemical transport models with higher spatial and temporal resolution and more refined speciation of HRVOCs are needed to better account for the near-source air quality impacts of large olefin flares.     

A Monte-Carlo Simulation of the Ozone Attainment Process

A Monte-Carlo simulation of the approach to attainment of the National Ambient Air Quality Standard for ozone has been performed for the California Bay Area Air Quality Management District. Four compliance tests together with different design values are used in the simulation. The results show that the present compliance test requiring a zero-percent chance of violation and the design value represented by the fourth highest value in three years makes both the standard and the control requirement much more stringent than generally assumed. In fact, to attain the standard on a long-term basis would require annual means and annual second-highest values that are close to those of the rural background ozone. The simulation also shows that by taking into account the fluctuation of ozone concentrations in the compliance test, such as a t test, and by using a design value consistent with the test, a standard defined in terms of the three-year mean of the annual second-highest values not only is more consistent with the currently- perceived stringency of the present standard, but may also be attainable with a more reasonable control requirement.     

Chemical Dynamics of Clouds at Mt. Mitchell,North Carolina

The role of clouds as the primary pathway for deposition of air pollutants into ecosystems has recently acquired much attention. Moreover, the acidity of clouds is highly variable over short periods of time. Cloud water collections were made at Mt. Mitchell State Park, North Carolina, using a real-time cloud and rain acidity/ conductivity (CRAC) analyzer during May to September 1987, 1988 and 1989 in an effort to explore extremes of chemical exposure. On the average, the mountain peak was exposed to cloud episodes about 70 percent of experimental days. The lowest pH of cloud water in nearly real-time (～10 min.) samples was 2.4, while that in hourly integrated samples was 2.6. The cloud pH during short cloud events (mean pH 3.1), whjch results from the orographic lifting mechanism, was lower than that during long cloud events (mean pH 3.5), which are associated with mesoscale or synoptic atmospheric disturbances. On the average, the pH values in nonprecipitating cloud events were about 0.4 pH unit lower than those in precipitating cloud events. Sulfate, nitrate, ammonium and hydrogen ions were found to be the major constituents of cloud water, and these accounted for -90 percent of the ionic concentration. Total ionic concentrations were found to be much higher in non-precipitating clouds (670-3,010 μeq/L) than those in precipitating clouds (220-370 μeq/L). At low acidity, ionic balance is sometimes not obtained. It is suggested that organic acids may provide this balance.

The profile of cloud water ionic concentration versus time was frequently observed to show decrease at the beginning and rising toward the end during short cloud events. Before the dissipation of clouds, a decrease in cloud water pH and an increase in ionic concentration were found. At the same time, temperature and solar radiation increased, and relative humidity and microphysical parameters (liquid water content, average droplet size, and droplet concentration) decreased. These observations suggest that evaporative dissipation of cloud droplets leads to acidification of cloud water. Mean pH of cloud water was 3.4 when the prevailing wind was from the northwest direction, and it was 3.9 when the wind was from the west direction. The effects of variations in cloud liquid water content have been separated from variations in pre-cloud pollutant concentrations to determine the relationship between source intensity and cloud water concentrations.     

Estimating the concentration of indoor particles of outdoor origin: A review

Recent toxicological results highlight the importance of separating exposure to indoor- and outdoor-generated particles, due to their different physicochemical and toxicological properties. In this framework, a number of studies have attempted to estimate the relative contribution of particles of indoor and outdoor origins to indoor concentrations, using either statistical analysis of indoor and outdoor concentration time-series or mass balance equations. The aim of this work is to review and compare the methodologies developed in order to determine the ambient particle infiltration factor (F _INF) (i.e., the fraction of ambient particles that enter indoors and remains suspended). The different approaches are grouped into four categories according to their methodological principles: (1) steady-state assumption using the steady-state form of the mass balance equation; (2) dynamic solution of the mass balance equation using complex statistical techniques; (3) experimental studies using conditions that simplify model calculations (e.g., decreasing the number of unknowns); and (4) infiltration surrogates using a particulate matter (PM) constituent with no indoor sources to act as surrogate of indoor PM of outdoor origin. Examination of the various methodologies and results reveals that estimating infiltration parameters is still challenging. The main difficulty lies in the separate calculation of penetration efficiency (P) and deposition rate (k). The values for these two parameters that are reported in the literature vary significantly. Deposition rate presents the widest range of values, both between studies and size fractions. Penetration efficiency seems to be more accurately calculated through the application of dynamic models. Overall, estimates of the infiltration factor generated using dynamic models and infiltration surrogates show good agreement. This is a strong argument in favor of the latter methodology, which is simple and easy to apply when chemical speciation data are available.

Implications: ?Taking into account that increased health risks may be related with ambient particles, a reliable estimation of the main parameters governing ambient particle infiltration indoors may assist towards the development of appropriate regulation and control measures, targeted to specific sources/factors contributing to increased exposures. The overall study of the methodological approaches estimating particle infiltration indoors suggests that dynamic models provide a more complete and realistic picture of ambient particle infiltration indoors, whereas the use of specific PM constituents to act as surrogates of indoor particles of outdoor origin seems also a promising new methodology.