Bacterial Emission Factors: A Foundation for the Terrestrial-Atmospheric Modeling of Bacteria Aerosolized by Wildland Fires

Wildland fire is a major global driver in the exchange of aerosols between terrestrial environments and the atmosphere. This exchange is commonly quantified using emission factors or the mass of a pollutant emitted per mass of fuel burned. However, emission factors for microbes aerosolized by fire have yet to be determined. Using bacterial cell concentrations collected on unmanned aircraft systems over forest fires in Utah, USA, we determine bacterial emission factors (BEFs) for the first time. We estimate that 1.39 × 1010 and 7.68 × 1011 microbes are emitted for each Mg of biomass consumed in fires burning thinning residues and intact forests, respectively. These emissions exceed estimates of background bacterial emissions in other studies by 3-4 orders of magnitude. For the ∼2631 ha of similar forests in the Fishlake National Forest that burn each year on average, an estimated 1.35 × 1017 cells or 8.1 kg of bacterial biomass were emitted. BEFs were then used to parametrize a computationally scalable particle transport model that predicted over 99% of the emitted cells were transported beyond the 17.25 x 17.25 km model domain. BEFs can be used to expand understanding of global wildfire microbial emissions and their potential consequences to ecosystems, the atmosphere, and humans.

Seasonal Emission Factors from Rangeland Prescribed Burns in the Kansas Flint Hills Grasslands

Operational-sized prescribed grassland burns at three mid-West U.S. locations and ten 1-ha-sized prescribed grassland burns were conducted in the Flint Hills of Kansas to determine emission factors and their potential seasonal effects. Ground-, aerostat-, and unmanned aircraft system-based platforms were used to sample plume emissions for a range of gaseous and particulate pollutants. The ten co-located, 1-ha-sized plots allowed for testing five plots in the spring and five in the late summer, allowing for control of vegetation type, biomass loading, climate history, and land use. The operational-sized burns provided a range of conditions under which to determine emission factors relevant to the Flint Hills grasslands. The 1-ha plots showed that emission factors for pollutants such as PM_2.5 and BTEX (benzene, toluene, ethylbenzene, and xylene) were higher during the late summer than during the traditional spring burn season. This is likely due to increased biomass density and fuel moisture in the growing season biomass resulting in reduced combustion efficiency.

Developing innovative treatment technologies for PFAS-containing wastes

The release of persistent per- and polyfluoroalkyl substances (PFAS) into the environment is a major concern for the United States Environmental Protection Agency (U.S. EPA). To complement its ongoing research efforts addressing PFAS contamination, the U.S. EPA's Office of Research and Development (ORD) commissioned the PFAS Innovative Treatment Team (PITT) to provide new perspectives on treatment and disposal of high priority PFAS-containing wastes. During its six-month tenure, the team was charged with identifying and developing promising solutions to destroy PFAS. The PITT examined emerging technologies for PFAS waste treatment and selected four technologies for further investigation. These technologies included mechanochemical treatment, electrochemical oxidation, gasification and pyrolysis, and supercritical water oxidation. This paper highlights these four technologies and discusses their prospects and the development needed before potentially becoming available solutions to address PFAS-contaminated waste.Implications: This paper examines four novel, non-combustion technologies or applications for the treatment of persistent per- and polyfluoroalkyl substances (PFAS) wastes. These technologies are introduced to the reader along with their current state of development and areas for further development. This information will be useful for developers, policy makers, and facility managers that are facing increasing issues with disposal of PFAS wastes.

Characterization of emissions from burning methyl-bromide-treated crop biomass

Alfalfa hay that was grown on a field treated with a methyl bromide and chloropicrin pesticide (at a 98/2 weight ratio) resulted in animal sickness, posing a disposal issue for the harvested feed. In consideration of disposal options, emissions and residues from burning treated and untreated alfalfa hay were sampled and analyzed to provide data for an assessment of potential health and environmental effects. Treated alfalfa hay was tested in parallel with untreated alfalfa in a controlled laboratory combustion facility. Results showed that about half of the bromine and chlorine in the treated hay was emitted and the remaining was retained in the ash. The alfalfa hay burned poorly, with modified combustion efficiencies, the ratio of CO₂ to CO + CO₂, below 0.89. The emission factor for PM_2.5 was statistically higher for the untreated versus treated alfalfa but the PAHs were doubled in the treated alfalfa. The treated alfalfa had significantly more emissions of polychorinated dibenzodioxin/dibenzofuran than the untreated alfalfa by a factor of 10, but less polybrominated dibenzodioxin/dibenzofuran. The high Br concentration in the treated alfalfa biomass may have resulted in formation and emission of mixed halogen compounds which were unable to be analyzed for lack of standards. Comparison of volatile organic compound emissions were unremarkable with the exception of MeBr where emissions from the treated alfalfa were over 300 times higher than the untreated biomass. The potential complications due to emissions and permitting of an open burn or contained incinerator left options for landfilling and feedstock blending for handling the treated alfalfa. Implications: This paper illustrates the issues agricultural managers must deal with concerning the combustive disposal of contaminated crops. A method is presented whereby combustion of contaminated crops can be assessed for their suitability for disposal by open air or enclosed burning.

Wildland fire smoke alters the composition, diversity, and potential atmospheric function of microbial life in the aerobiome

The atmosphere contains a diverse reservoir of microbes but the sources and factors contributing to microbial aerosol variability are not well constrained. To advance understanding of microbial emissions in wildfire smoke, we used unmanned aircraft systems to analyze the aerosols above high-intensity forest fires in the western United States. Our results show that samples of the smoke contained ~four-fold higher concentrations of cells (1.02 ± 0.26 × 105 m-3) compared to background air, with 78% of microbes in smoke inferred to be viable. Fivefold higher taxon richness and ~threefold enrichment of ice nucleating particle concentrations in smoke implies that wildfires are an important source of diverse bacteria and fungi as well as meteorologically relevant aerosols. We estimate that such fires emit 3.71 × 1014 microbial cells ha-1 under typical wildfire conditions in western US forests and demonstrate that wildland biomass combustion has a large-scale influence on the local atmospheric microbial assemblages. Given the long-range transport of wildfire smoke emissions, these results expand the concept of a wildfire's perimeter of biological impact and have implications to biogeography, gene flow, the dispersal of plant, animal, and human pathogens, and meteorology.

Analysis of emissions and residue from methods to improve efficiency of at-sea, in situ oil spill burns

The combustion efficiency of simulated at-sea surface oil burns (in situ burns) was determined in a 63 m³ tank while testing varied boom configurations and air-assist nozzles in the presence and absence of waves. Combustion efficiencies of Alaska North Slope oil based on unburned carbon in the plume emissions ranged from 85% to 93% while values based on oil mass loss ranged from 89% to 99%. A four-fold variation in PM_2.5 emission factors was observed from the test conditions. The most effective burns in terms of reduced emissions and post-burn residue concentration of total petroleum hydrocarbons were those that had high length to width boom ratios resulting in higher flame front surface area exposure to ambient air. The amount of oil mass lost was not related to any combustion efficiency parameters measured in the plume, representing a potential tradeoff between unburnt oil and air pollution.

Supercritical Water Oxidation as an Innovative Technology for PFAS Destruction

Water above 374 °C and 22.1 MPa, becomes supercritical, a special state where organic solubility increases and oxidation processes are accelerated. Supercritical water oxidation (SCWO) has been previously shown to destroy hazardous substances such as halogenated compounds. Three separate providers of SCWO technology were contracted to test the efficacy of SCWO systems to reduce per- and poly-fluoroalkyl substances (PFAS) concentrations from solutions of dilute aqueous film-forming foam (AFFF). The findings of all three demonstration studies, showed greater than 99% reduction of the total PFAS identified in a targeted-compound analysis, including perfluorooctanesulfonic acid (PFOS) and perfluorooctanoic acid (PFOA). PFOS was reduced from 26.2 mg/L to 240 μg/L, 30.4 mg/L to 0.310 μg/L, and 190 mg/L to 8.57 μg/L, from the Aquarden, Battelle, and 374Water demonstrations, respectively. Similarly, PFOA was reduced from 930 to 0.14 μg/L, 883 to 0.102 μg/L, and 3,100 μg/L to non-detect in the three evaluations. Additionally, chemical oxygen demand of the dilute AFFF was shown to reduce from 4,750 to 5.17 mg/L after treatment, indicating significant organic compound destruction. In one demonstration, a mass balance of the influent and effluent found that the targeted compounds accounted for only 27% of the generated fluoride, suggesting that more PFAS were destroyed than measured and emphasizing the limitations of targeted analysis alone. As a destructive technology, SCWO may be an alternative to incineration and could be a permanent solution for PFAS-laden wastewaters rather than disposal by injection into a deep-well or landfilling. Additional investigation of reaction by-products remains to be conducted for a complete assessment of SCWO's potential as a safe and effective PFAS treatment technology.

Wildland Fire Emission Sampling at Fishlake National Forest, Utah Using an Unmanned Aircraft System

Emissions from a stand replacement prescribed burn were sampled using an unmanned aircraft system (UAS, or "drone") in Fishlake National Forest, Utah, U.S.A. Sixteen flights over three days in June 2019 provided emission factors for a broad range of compounds including carbon monoxide (CO), carbon dioxide (CO₂), nitric oxide (NO), nitrogen oxide (NO₂), particulate matter < 2.5 microns in diameter (PM_2.5), volatile organic compounds (VOCs) including carbonyls, black carbon, and elemental/organic carbon. To our knowledge, this is the first UAS-based emission sampling for a fire of this magnitude, including both slash pile and crown fires resulting in wildfire-like conditions. The burns consisted of drip torch ignitions as well as ground-mobile and aerial helicopter ignitions of large stands comprising over 1,000 ha, allowing for comparison of same-species emission factors burned under different conditions. The use of a UAS for emission sampling minimizes risk to personnel and equipment, allowing flexibility in sampling location and ensuring capture of representative, fresh smoke constituents. PM_2.5 emission factors varied 5-fold and, like most pollutants, varied inversely with combustion efficiency resulting in lower emission factors from the slash piles than the crown fires.

Use of an unmanned aircraft system to quantify NO x emissions from a natural gas boiler

Aerial emission sampling of four natural gas boiler stack plumes was conducted using an unmanned aerial system (UAS) equipped with a lightweight sensor-sampling system (the "Kolibri") for measurement of nitrogen oxide (NO), and nitrogen dioxide (NO₂), carbon dioxide (CO₂), and carbon monoxide (CO). Flights (n=22) ranged from 11 to 24min in duration at two different sites. The UAS was maneuvered into the plumes with the aid of real-time CO₂ telemetry to the ground operators and, at one location, a second UAS equipped with an infrared-visible camera. Concentrations were collected and recorded at 1Hz. The maximum CO₂, CO, NO, and NO₂ concentrations in the plume measured were 10000, 7, 27, and 1.5 ppm, respectively. Comparison of the NO _x emissions between the stack continuous emission monitoring systems and the UAS-Kolibri for three boiler sets showed an average of 5.6% and 3.5% relative difference for the run-weighted and carbon-weighted average emissions, respectively. To our knowledge, this is the first evidence of the accuracy performance of UAS-based emission factors against a source of known strength.

Use of an unmanned aircraft system to quantify NO x emissions from a natural gas boiler

Aerial emission sampling of four natural gas boiler stack plumes was conducted using an unmanned aerial system (UAS) equipped with a lightweight sensor-sampling system (the "Kolibri") for measurement of nitrogen oxide (NO), and nitrogen dioxide (NO₂), carbon dioxide (CO₂), and carbon monoxide (CO). Flights (n=22) ranged from 11 to 24min in duration at two different sites. The UAS was maneuvered into the plumes with the aid of real-time CO₂ telemetry to the ground operators and, at one location, a second UAS equipped with an infrared-visible camera. Concentrations were collected and recorded at 1Hz. The maximum CO₂, CO, NO, and NO₂ concentrations in the plume measured were 10000, 7, 27, and 1.5 ppm, respectively. Comparison of the NO _x emissions between the stack continuous emission monitoring systems and the UAS-Kolibri for three boiler sets showed an average of 5.6% and 3.5% relative difference for the run-weighted and carbon-weighted average emissions, respectively. To our knowledge, this is the first evidence of the accuracy performance of UAS-based emission factors against a source of known strength.

Combustion by-products and their health effects: Summary of the 16th international congress

The 16th International Congress on Combustion By-Products and their Health Effects (PIC2019) was held in Ann Arbor, Michigan, from July 10 to 12, 2019. For the last 28 years, this conference has served as an interdisciplinary platform for the discussion of the formation, environmental fate, health effects, policy, and remediation of combustion by-products. The technical areas for PIC2019 included mobile and stationary sources in urban environments, open fires, indoor air pollution, and halogenated pollutants. The congress was sponsored by the National Institute of Environmental Health Sciences (NIEHS), the U.S. EPA, the School of Public Health at the University of Michigan, the Civil and Environmental Engineering Department at the University of Michigan, the Mechanical Engineering Department at the University of Michigan, the Aerospace Engineering Department at the University of Michigan, and the Climate and Space Sciences and Engineering Department at the University of Michigan. Special features of the conference included a career path and round table discussion on translating research and engaging communities.

Improving post-detonation energetics residues estimations for the Life Cycle Environmental Assessment process for munitions

The Life Cycle Environmental Assessment (LCEA) process for military munitions tracks possible environmental impacts incurred during all phases of the life of a munition. The greatest energetics-based emphasis in the current LCEA process is on manufacturing. A review of recent LCEAs indicates that energetics deposition on ranges from detonations and disposal during training is only peripherally examined through assessment of combustion products derived from closed-chamber testing or models. These assessments rarely report any measurable energetic residues. Field-testing of munitions for energetics residues deposition has demonstrated that over 30% of some energetic compounds remain after detonation, which conflicts with the LCEA findings. A study was conducted in the open environment to determine levels of energetics residue deposition and if combustion product results can be correlated with empirical deposition results. Energetics residues deposition, post-detonation combustion products, and fine aerosolized energetics particles following open-air detonation of blocks of Composition C4 (510 g RDX/block) were quantified. The deposited residues amounted to 3.6 mg of energetic per block of C4, or less than 0.001% of the original energetics. Aerial emissions of energetics were about 7% of the amount of deposited energetics. This research indicates that aerial combustion products analysis can provide a valuable supplement to energetics deposition data in the LCEA process but is insufficient alone to account for total residual energetics. This study demonstrates a need for the environmental testing of munitions to quantify energetics residues from live-fire training.

Characterizing emissions from open burning of military food waste and ration packaging compositions

Emissions from open burning of military food waste and ration packaging compositions were characterized in response to health concerns from open burning disposal of waste, such as at military forward operating bases. Emissions from current and prototype Meals, Ready-to-Eat (MREs), and material options for their associated fiberboard packaging were quantified to assess contributions of the individual components. MREs account for 67-100% of the particulate matter (PM), volatile organic compounds (VOCs), polycyclic aromatic hydrocarbons (PAHs), and polychlorinated dibenzo-p-dioxins and -furans (PCDDs/PCDFs) emissions when burned in unison with the current fiberboard container and liner. The majority of the particles emitted from these burns are of median diameter 2.5 μm (PM_2.5). Metal emission factors were similar regardless of waste composition. Measurements of VOCs and PAHs indicate that targeted replacement of MRE components may be more effective in reducing emissions than variation of fiberboard-packaging types. Despite MRE composition variation, equivalent emission factors for PM, PAH, VOC, and PCDD/PCDF were seen. Similarly, for fiberboard packaging, composition variations exhibited essentially equivalent PM, PAH, VOC, and PCDD/PCDF emission factors amongst themselves. This study demonstrated a composition-specific analysis of waste burn emissions, assessing the impact of waste component substitution using military rations.

Field Determination of Multipollutant, Open Area Combustion Source Emission Factors with a Hexacopter Unmanned Aerial Vehicle

An emission sensor/sampler system was coupled to a National Aeronautics and Space Administration (NASA) hexacopter unmanned aerial vehicle (UAV) to characterize gases and particles in the plumes emitted from open burning of military ordnance. The UAV/sampler was tested at two field sites with test and sampling flights spanning over 16 hours of flight time. The battery-operated UAV was remotely maneuvered into the plumes at distances from the pilot of over 600 m and at altitudes of up to 122 m above ground level. While the flight duration could be affected by sampler payload (3.2 to 4.6 kg) and meteorological conditions, the 57 sampling flights, ranging from 4 to 12 min, were typically terminated when the plume concentrations of CO2 were diluted to near ambient levels. Two sensor/sampler systems, termed "Kolibri," were variously configured to measure particulate matter, metals, chloride, perchlorate, volatile organic compounds, chlorinated dioxins/furans, and nitrogen-based organics for determination of emission factors. Gas sensors were selected based on their applicable concentration range, light weight, freedom from interferents, and response/recovery times. Samplers were designed, constructed, and operated based on U.S. Environmental Protection Agency (EPA) methods and quality control criteria. Results show agreement with published emission factors and good reproducibility (e.g., 26% relative standard deviation for PM2.5). The UAV/Kolibri represents a significant advance in multipollutant emission characterization capabilities for open area sources, safely and effectively making measurements heretofore deemed too hazardous for personnel or beyond the reach of land-based samplers.

A small, lightweight multipollutant sensor system for ground-mobile and aerial emission sampling from open area sources

Characterizing highly dynamic, transient, and vertically lofted emissions from open area sources poses unique measurement challenges. This study developed and applied a multipollutant sensor and time-integrated sampler system for use on mobile applications such as vehicles, tethered balloons (aerostats) and unmanned aerial vehicles (UAVs) to determine emission factors. The system is particularly applicable to open area sources, such as forest fires, due to its light weight (3.5 kg), compact size (6.75 L), and internal power supply. The sensor system, termed "Kolibri", consists of sensors measuring CO₂ and CO, and samplers for particulate matter (PM) and volatile organic compounds (VOCs). The Kolibri is controlled by a microcontroller which can record and transfer data in real time through a radio module. Selection of the sensors was based on laboratory testing for accuracy, response delay and recovery, cross-sensitivity, and precision. The Kolibri was compared against rack-mounted continuous emissions monitoring system (CEMs) and another mobile sampling instrument (the "Flyer") that has been used in over ten open area pollutant sampling events. Our results showed that the time series of CO, CO₂, and PM_2.5 concentrations measured by the Kolibri agreed well with those from the CEMs and the Flyer, with a laboratory- tested percentage error of 4.9%, 3%, and 5.8%, respectively. The VOC emission factors obtained using the Kolibri were consistent with existing literature values that relate concentration to combustion efficiency. The potential effect of rotor downwash on particle sampling was investigated in an indoor laboratory and the preliminary results suggested that its influence is minimal. Field application of the Kolibri sampling open detonation plumes indicated that the CO and CO₂ sensors responded dynamically and their concentrations co-varied with emission transients. The Kolibri system can be applied to various challenging open area scenarios such as fires, lagoons, flares, and landfills.

Characterization of Size-Fractionated Airborne Particles Inside an Electronic Waste Recycling Facility and Acute Toxicity Testing in Mice

Disposal of electronic waste (e-waste) in landfills, incinerators, or at rudimentary recycling sites can lead to the release of toxic chemicals into the environment and increased health risks. Developing e-waste recycling technologies at commercial facilities can reduce the release of toxic chemicals and efficiently recover valuable materials. While these e-waste operations represent a vast improvement over previous approaches, little is known about environmental releases, workplace exposures, and potential health impacts. In this study, airborne particulate matter (PM) was measured at various locations within a modern U.S.-based e-waste recycling facility that utilized mechanical processing. In addition, composite size fractionated PM (coarse, fine and ultrafine) samples were collected, extracted, chemically analyzed, and given by oropharyngeal aspiration to mice or cultured with lung slices for lung toxicity tests. Indoor total PM concentrations measured during the study ranged from 220 to 1200 μg/m(3). In general, the coarse PM (2.5-10 μm) was 3-4 times more abundant than fine/ultrafine PM (<2.5 μm). The coarse PM contained higher levels of Ni, Pb, and Zn (up to 6.8 times) compared to the fine (0.1-2.5 μm) and ultrafine (<0.1 μm) PM. Compared to coarse PM measurements from a regional near-roadway study, Pb and Ni were enriched 170 and 20 times, respectively, in the indoor PM, with other significant enrichments (>10 times) observed for Zn and Sb, modest enrichments (>5 times) for Cu and Sr, and minor enrichments (>2 times) for Cr, Cd, Mn, Ca, Fe, and Ba. Negligible enrichment (<2 times) or depletion (<1 time) were observed for Al, Mg, Ti, Si, and V. The coarse PM fraction elicited significant pro-inflammatory responses in the mouse lung at 24 h postexposure compared to the fine and ultrafine PM, and similar toxicity outcomes were observed in the lung slice model. We conclude that exposure to coarse PM from the facility caused substantial inflammation in the mouse lung and enrichment of these metals compared to levels normally present in the ambient PM could be of potential health concern.

Combustion By-Products and their Health Effects--combustion engineering and global health in the 21st century: issues and challenges

The 13th International Congress on Combustion By-Products and their Health Effects was held in New Orleans, Louisiana from May 15 to 18, 2013. The congress, sponsored by the Superfund Research Program, National Institute of Environmental Health Sciences, and National Science Foundation, brought together international academic and government researchers, engineers, scientists, and policymakers. With industrial growth, increased power needs and generation and coal consumption and their concomitant emissions, pernicious health effects associated with exposures to these emissions are on the rise. This congress provides a unique platform for interdisciplinary exchange and discussion of these topics. The formation, conversion, control, and health effects of combustion by-products, including particulate matter and associated heavy metals, persistent organic pollutants, and environmentally persistent free radicals, were discussed during the congress. This review will summarize and discuss the implications of the data presented.

Effect of moisture, charge size, and chlorine concentration on PCDD/F emissions from simulated open burning of forest biomass

Loblolly pine (Pinus taeda) was combusted at different charge sizes, fuel moisture, and chlorine content to determine the effect on emissions of polychlorinated dibenzo-p-dioxins and polychlorinated dibenzofurans (PCDDs/Fs) as well as copollutants CO, PM, and total hydrocarbons. The experiments were performed in an enclosed chamber under conditions simulating open, prescribed burns of forest biomass. Burn progress was monitored through on line measurement of combustion gases and temperature while PCDD/F concentrations were determined by ambient sampling methods. PCDD/F toxic equivalency (TEQ) and total (tetra- to octa-CDD/F) emission factors were independent of charge size (1-10 kg) and moisture content (7-50%). However, the lower chlorinated, mono- to tri-CDD/F compounds were increased by poor combustion conditions: combustion efficiency lower than 0.919 was generally found when the moisture content was higher than 30%. The increase of fuel matrix chlorine from 0.04% to 0.8% using a brine bath resulted in about a 100-fold increase of PCDD/F to about 90 ng TEQ/kg of carbon burned, C(b). These emission factors were linearly dependent on Cl concentration in the biomass. PCDD 2,3,7,8-Cl-substituted congeners and homologue patterns were also influenced by the addition of chlorine resulting in emissions with a higher abundance of the most toxic congeners (TeCDD and PeCDD). When both chlorine and moisture content were increased in the fuel, a simultaneous effect of the two parameters was observed. The increased TEQ values expected from higher Cl concentrations were mitigated by the presence of water, giving MCE = 0.868, promoting formation of mono- to tri-PCDD/F, and lowering the TEQ value. Open burn simulations were used to study PCDD/F formation in different combustion conditions providing a mathematical correlation between PCDD/F emissions and chlorine and moisture content in the fuel.

Detection of indoor biological hazards using the man-portable laser induced breakdown spectrometer

The performance of a man-portable laser induced breakdown spectrometer was evaluated for the detection of biological powders on indoor office surfaces and wipe materials. Identification of pure unknown powders was performed by comparing against a library of spectra containing biological agent surrogates and confusant materials, such as dusts, diesel soot, natural and artificial sweeteners, and drink powders, using linear correlation analysis. Simple models constructed using a second technique, partial least squares discriminant analysis, successfully identified Bacillus subtilis (BG) spores on wipe materials and office surfaces. Furthermore, these models were able to identify BG on materials not used in the training of the model.

Laser-induced breakdown spectroscopy for the classification of unknown powders

Laser-induced breakdown spectroscopy (LIBS) was used to discern between two biological agent surrogates (Bacillus atrophaeus and ovalbumin) and potential interferent compounds (mold spores, humic acid, house dust, and Arizona road dust). Multiple linear regression and neural network analysis models were constructed by using B. atrophaeus and ovalbumin spectra, and limits of detection were calculated. Classification of the agent surrogates' LIBS spectra was attempted by using a neural network model. False negative rates of 0% were observed for B. atrophaeus (100 colony forming units) spore spectra with the neural network model used for classification.

Report: Combustion Byproducts and Their Health Effects: Summary of the 10th International Congress

The 10th International Congress on Combustion Byproducts and their Health Effects was held in Ischia, Italy, from June 17-20, 2007. It is sponsored by the US NIEHS, NSF, Coalition for Responsible Waste Incineration (CRWI), and Electric Power Research Institute (EPRI). The congress focused on: the origin, characterization, and health impacts of combustion-generated fine and ultrafine particles; emissions of mercury and dioxins, and the development/application of novel analytical/diagnostic tools. The consensus of the discussion was that particle-associated organics, metals, and persistent free radicals (PFRs) produced by combustion sources are the likely source of the observed health impacts of airborne PM rather than simple physical irritation of the particles. Ultrafine particle-induced oxidative stress is a likely progenitor of the observed health impacts, but important biological and chemical details and possible catalytic cycles remain unresolved. Other key conclusions were: (1) In urban settings, 70% of airborne fine particles are a result of combustion emissions and 50% are due to primary emissions from combustion sources, (2) In addition to soot, combustion produces one, possibly two, classes of nanoparticles with mean diameters of ~10 nm and ~1 nm. (3) The most common metrics used to describe particle toxicity, viz. surface area, sulfate concentration, total carbon, and organic carbon, cannot fully explain observed health impacts, (4) Metals contained in combustion-generated ultrafine and fine particles mediate formation of toxic air pollutants such as PCDD/F and PFRs. (5) The combination of metal-containing nanoparticles, organic carbon compounds, and PFRs can lead to a cycle generating oxidative stress in exposed organisms.

Kinetic modeling of polychlorinated dibenzo-p-dioxin and dibenzofuran formation based on carbon degradation reactions

Combustion experiments in a laboratory-scale fixed bed reactor were performed to determine the role of temperature and time in polychlorinated dibenzo-p-dioxin (PCDD) and polychlorinated dibenzofuran (PCDF) formation, allowing a global kinetic expression to be written for PCDD/F formation due to soot oxidation in fly ash deposits. Rate constants were calculated for the reactions of carbon degradation, PCDD/F formation, desorption, and degradation. For the first time, values for activation and thermodynamic parameters for the overall reactions have been calculated for PCDD/F formation, desorption, and destruction reactions. Good agreement was found between the calculated rate constants for carbon degradation and for PCDD/F formation, indicating that the two processes have a common rate-determining step. Moreover, PCDD/F formation was found to be still active after long reaction times (24 h). These results points out the importance of carbon deposits in the postcombustion stages that can account for emissions long after their formation (memory effects). The calculated formation rates were 7-15 times higher than those reported in the literature from fly ash-only experiments, indicating the importance of both soot and a continuous source of chlorine. A comparison between full-scale incinerator rates and model calculated rates indicates that our model based on carbon degradation kinetic can be a tool to estimate emissions.

Traffic and meteorological impacts on near-road air quality: summary of methods and trends from the Raleigh Near-Road Study

A growing number of epidemiological studies conducted worldwide suggest an increase in the occurrence of adverse health effects in populations living, working, or going to school near major roadways. A study was designed to assess traffic emissions impacts on air quality and particle toxicity near a heavily traveled highway. In an attempt to describe the complex mixture of pollutants and atmospheric transport mechanisms affecting pollutant dispersion in this near-highway environment, several real-time and time-integrated sampling devices measured air quality concentrations at multiple distances and heights from the road. Pollutants analyzed included U.S. Environmental Protection Agency (EPA)-regulated gases, particulate matter (coarse, fine, and ultrafine), and air toxics. Pollutant measurements were synchronized with real-time traffic and meteorological monitoring devices to provide continuous and integrated assessments of the variation of near-road air pollutant concentrations and particle toxicity with changing traffic and environmental conditions, as well as distance from the road. Measurement results demonstrated the temporal and spatial impact of traffic emissions on near-road air quality. The distribution of mobile source emitted gas and particulate pollutants under all wind and traffic conditions indicated a higher proportion of elevated concentrations near the road, suggesting elevated exposures for populations spending significant amounts of time in this microenvironment. Diurnal variations in pollutant concentrations also demonstrated the impact of traffic activity and meteorology on near-road air quality. Time-resolved measurements of multiple pollutants demonstrated that traffic emissions produced a complex mixture of criteria and air toxic pollutants in this microenvironment. These results provide a foundation for future assessments of these data to identify the relationship of traffic activity and meteorology on air quality concentrations and population exposures.

Mechanistic relationships among PCDDs/Fs, PCNs, PAHs, CIPhs, and CIBzs in municipal waste incineration

An extensive investigation was conducted to understand polychlorinated dibenzo-p-dioxin and furan (PCDD/F) formation mechanisms and their relationship with other organic compounds. PCDD/F, chlorophenols (CIPhs), chlorobenzenes (CIBzs), polyaromatic hydrocarbons (PAHs), and polychlorinated naphthalenes (PCNs) were analyzed in the boiler exit gases of a field-scale municipal solid waste incinerator under various operating conditions. The TEQ value and the concentration of target compounds changed with incinerator operating conditions. Low mass PAHs and 246-triCIPh increased dramatically during shut downs; the latter was associated with increased 1368- and 1379-TeCDD. A strong correlation was observed between PCNs and PCDFs and adjacent PCNs homologue group were closely related to each other. This suggested that PCN formation is related with chlorination/dechlorination mechanisms similar to PCDFs. PCDDs were related with most of the CIPhs and the high chlorinated benzenes. Most of target compounds except PAHs had a positive correlation (R2 > 0.5) with TEQ and half of them showed a good relationship (R2 > 0.8) with PCDDs/Fs toxic equivalency (TEQ).

Development of size-selective sampling of Bacillus anthracis surrogate spores from simulated building air intake mixtures for analysis via laser-induced breakdown spectroscopy

Size-selective sampling of Bacillus anthracis surrogate spores from realistic, common aerosol mixtures was developed for analysis by laser-induced breakdown spectroscopy (LIBS). A two-stage impactor was found to be the preferential sampling technique for LIBS analysis because it was able to concentrate the spores in the mixtures while decreasing the collection of potentially interfering aerosols. Three common spore/aerosol scenarios were evaluated, diesel truck exhaust (to simulate a truck running outside of a building air intake), urban outdoor aerosol (to simulate common building air), and finally a protein aerosol (to simulate either an agent mixture (ricin/anthrax) or a contaminated anthrax sample). Two statistical methods, linear correlation and principal component analysis, were assessed for differentiation of surrogate spore spectra from other common aerosols. Criteria for determining percentages of false positives and false negatives via correlation analysis were evaluated. A single laser shot analysis of approximately 4 percent of the spores in a mixture of 0.75 m(3) urban outdoor air doped with approximately 1.1 x 10(5) spores resulted in a 0.04 proportion of false negatives. For that same sample volume of urban air without spores, the proportion of false positives was 0.08.