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

Abstract

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.

1. Introduction

The International Congress on Combustion By-Products and their Health Effects represents an interdisciplinary platform for discussions on the formation, environmental fate, health effects, policy and remediation of combustion by-products. For the last 28 years, the location of this event has rotated among the United States, Europe, and Asia. On July 10, 2019, Dr. Angela Violi and Dr. Paolo Elvati hosted the 16th International Congress on Combustion By-Products and their Health Effects (PIC2019) at the University of Michigan campus. Fig. 1 reports the logo created for the PIC2019 congress. Major conference themes included Mobile and Stationary Sources in Urban Environment, Open Fires, Indoor Pollution, and Halogenated Pollutants. Five outstanding speakers were invited for the plenary lectures. On the first day of the congress, Dr. Danielle Carlin, from the National Institute of Environmental Health Sciences (NIEHS) branch of Hazardous Substances Research, introduced the keynote speaker, Dr. Richard T. Di Giulio, from Duke University. Dr. Di Giulio discussed the environmental contamination of polycyclic aromatic hydrocarbons (PAHs). The second keynote speaker, Dr. Lupita Montoya, from the University of Colorado Boulder, was introduced by Dr. Andre Boehman, from the University of Michigan. The second day featured keynote speakers Dr. David M. DeMarini, from U.S. EPA, and Dr. Heildelore Fielder, from Örebro University in Sweden, introduced, respectively, by Dr. Brian Gullett, from the U.S. EPA Office of Research and Development, and Dr. Stina Jansson, from Umeå University in Sweden. The final keynote speaker, Andre Boehman, University of Michigan, was introduced by Dr. Ralf Zimmermann from the Helmholz Zentrum München (HMGU) in Germany. The audience was composed of academic and industrial researchers, clinicians and clinician scientists, governmental officials, and stakeholders.

Fig. 1.

Congress Logo. 16th International Congress on Combustion By-Products and Their Health Effects Logo.

Here, we present a Symposia Review, summarizing the scientific contributions and events of those who attended the 16th International Congress on Combustion By-Products and Their Health Effects. The Symposia Review is organized into sections, representing the four main technical areas under scrutiny at the congress, including Mobile and Stationary Sources in Urban Environment, Open Fires, Indoor Air Pollution, and Halogenated Pollutants. The review also summarizes the scientific poster session and the round table discussion on the subject of “Translating Research and Engaging Communities”. A snapshot of the attendees is showed in Fig. 2.

Fig. 2.

PIC2019 Congress Group Photo. Gathered attendees of the conference posing for picture.

2. Mobile and Stationary Sources in Urban Environments

Several sessions at the PIC 2019 conference presented the subject of mobile and stationary sources in urban environments.

The plenary lecture of Andre Boehman (University of Michigan) showed that different fuels (e.g. biofuel and combustion conditions in diesel engines (i.e. premixed charged-compression ignition)) have a strong impact on the structure of the emitted soot (e.g. amorphous soot, bent or straight graphene layers and particle size distribution) [1]. It is likely that these different soot structures have different toxicological impact [2], [3], [4]. The lecture by V. Hensel and A. Mayer pointed out how efficiently the particles can be removed by modern particle filters. A new challenge is direct injection gasoline engines, which also are generating a large number of soot particulates albeit in a smaller particle size range compared to diesel engines (nanoparticles). This challenge requires improvements in particle filter technologies.

A session chaired by Ralf Zimmermann (HMGU) focused on the formation and toxicological effects of combustion aerosols, with a partial focus on the particulates. The session reflected the multidisciplinary facets of the aerosol and health topic. The chimeric, often inconclusive appearance of observed toxicological and epidemiological findings is caused by the complexity of combustion aerosols and the multitude of biological pathways which can be triggered by the aerosol gasand particle-phase chemical composition, physical particle properties and the interaction of gaseous compounds and aerosol particles. These aerosols result in both synergistic and antagonistic actions on biological reactions. Atmospheric reactions of combustion gases and particles have an effect upon air composition quality.

Ian Gilmour (U.S. EPA/ORD) reported results obtained by a unique biomass combustion simulator for smoldering and flaming combustion, allowing the reproducible inhalation exposure of mice to biomass smoke. An interesting outcome is that flaming combustion of biomass (wood, peat etc.) can generate a more toxic aerosol than smoldering combustion, even while the particulate matter (PM) concentration is about an order of magnitude large in the latter case.

The last talk in the session by Jennifer Irving, Louisiana State University, presented an adapted NIEHS framework for use in developing research strategies that advance basic research in chemistry and environmental science into translational research categories that have the potential to impact human health. It is anticipated that such a framework can be applied to other research programs studying emerging contaminants. This framework could be used to help researchers in the field of basic combustion by-products determine the health implications of their research.

2.1. Qingyu Li

Qingyu Li (PhD candidate, Hunan University; Department of Mechanical Engineering, University of Michigan) explored new methodologies to optimize fuel injection strategies in a production direct injection spark ignition (DISI) engine, with the aim of simultaneously minimizing gasoline fuel consumption and particulate emissions. DISI engines improve fuel efficiency in comparison with port fuel injection engines but can produce higher particulate emissions. Current fuel injection technology has dramatically expanded the operating space to improve engine performance (including reducing particulate emissions) using multiple injections per cycle. However, the increased number of control variables make engine optimization and calibration significantly more arduous. In this work, an optimization process based on minimization of a target function that considers brake specific fuel consumption and the levels of engine-out particulate emissions, is demonstrated using different steady-state engine operating conditions. The control variables were the injection timing and the fuel mass distribution in the different injection events, which are the most influential engine operating parameters on fuel consumption and engine-out emissions. The performance of the optimization algorithm, based on a genetic algorithm, is demonstrated and compared with the production calibration. The results show low fuel consumption and low particulate conditions are found by the genetic algorithm and the outcomes can yield significant reductions in particulates while minimizing time resources. Future work will further explore the effects of the input parameters to the genetic algorithm, e.g., increased gene population, and focus on opportunities for improvement during transient engine operation.

2.2. Bogdan Z. Dlugogorski

Bogdan Z. Dlugogorski (Office of Deputy Vice Chancellor Research & Innovation, Charles Darwin University, Australia) and his colleagues at the FireSafety and Combustion Laboratory at Murdoch University in Australia investigated the atmospheric oxidation process of carbon disulfide (CS₂), as the initial step to account for the formation of the most abundant sulfur carrier in atmosphere, carbonyl sulfide (COS), and the precursor of acid rain, sulfur dioxide (SO₂). Density-functional calculations at the theory level of M062X facilitated the exploration of the path ways for CS₂ + O₂ and CS₂ + OH + O₂. Direct oxidation between CS₂ and O₂ is too slow to account for the fast conversion of CS₂ to COS in atmosphere, with a remarkably-high activation barrier at 223 kJ/mol. Rather, the OH radical acts as the initial atmospheric oxidiser for CS₂. The produced S-adduct, SCS(OH), further reacts with O₂, yielding COS and HOSO with a trivial activation energy at 19.3 kJ/mol. Subsequent oxidation of HOSO is rather facile with a shallow barrier at 7.6 kJ/mol, giving HO₂ and SO₂ as final products. This study depicts the fate of important sulfur emission – CS₂, in the atmosphere. As the major sulfur carrier in atmosphere with an extensively long-life time of more than one year, COS deserves further investigation.

2.3. J. Passig

J. Passig and colleagues at the University of Rostock and Helmholtz Zentrum München and Photonion GmbH presented “New Developments and Applications in Single Particle Aerosol Mass Spectrometry: Simplified Simultaneous Detection of Polycyclic Aromatic Hydrocarbons and Elements”. Single particle chemical data is important to understand the mechanism of health effects, as the particles in the size range 300 nm – 0.8 µm are delivering the highest dose of toxic components (PAHs and metals) to the human lung. The aspect of internal or external mixing of pollutants in the particle ensemble is becoming very important: It defines the local toxicant dose that a single particle can deliver to an individual lung cell (e.g. an epithelial cell or a macrophage). Currently, the only on-line measuring method which can discern the mixing state of aerosol particle properties is single particle mass spectrometry. However, in order to allow a more comprehensive coverage of important air toxicants, further developments are required. A new optical approach combines the LDI process (laser desorption/ionisation), which ionizes metals, complex ions (nitrate, sulfate etc.) and soot (as carbon clusters), and laser desorption – resonance enhanced multiphoton ionisation process (REMPI), which analyzes the PAHs. For the first time, a comprehensive characterization of some of the most important air toxicants in single particle mass spectrometry (SPMS) was realized [5]. First applications show that different pattern of PAH and elements (in particular health relevant transition metals) can be detected from different sources. For example, long range transport of coal combustion (containing lead) and wood combustion particles from Eastern Europe could be detected in Rostock, Germany. Furthermore, they identified a resonance effect in LDI (RELDI – Resonance Enhanced LDI) which increases detectability (e.g. iron, vanadium and nickel) using a 248 nm Excimer laser for LDI [6]. This effect allows one to use the SPMS for efficient detection of plumes form ships using bunker fuel (with and without a sulfur scrubber). This is important as PM from ships is particularly important for adverse health effects. More SPMS data are needed to better evaluate the effect of internal/external mixing of air toxicants on PM on health effects. With the new SPMS technology a reasonably rugged instrument is available. Further applications of ship engine emission and monitoring as well as the combined use of SPMS with biological exposure experiments are currently underway. The system has recently been made commercially available for other researchers via a spin-off company of the research group Photonion GmbH.

2.4. Andreas Mayer

Andreas Mayer and team at Verification of Emission Reduction Technology (VERT), a worldwide active organization to promote best available emission reduction technology for combustion engines, presented on a “New Periodical Technical Inspection (N-PTI) for light duty vehicles and heavy duty vehicles (LDV and HDV) to guarantee emission quality”. Filters and catalysts are able to clean the exhaust gas from internal combustion engines (ICE), but this technology is very new and there might be effects which are not taken into account by the manufacturer. The technology effectiveness might also depend on operation profiles, maintenance, engine age, meteorological conditions, catalyst poisoning effects and the potential for user tampering. The research team explored how to find vehicles in the in-use fleet that are not performing well in order to repair or replace the damaged elements. They concentrated on the most toxic (and carcinogenic) substances, which are the submicrometer solid particles and can be counted by different physical principles like condensation particle counters (CPCs) or diffusion charging (DC), followed by electric measurements. A well-performing diesel particulate filter (DPF) or gasoline particle filter (GPF) should result in a particle number concentration below 10,000 cm⁻³ whereas the raw emission of the engine will be in the range of 1,000,000 cm⁻³ or higher, so it should be relatively easy to detect DPF failures. The test should be short and simple, preferably with a stationary vehicle at engine idling conditions and the time to measure should not exceed 1–2 min. With these conditions met, this test could be accepted as a periodic technical inspection (PTI) of each vehicle in operation annually. Fleets of up to 2000 mixed vehicles were performed in 2016/17/18 by partner laboratories of the N-PTI group in the Netherlands, Belgium, Switzerland and Spain. In the first test period already available instruments have been used resulting in failure rates of 10–15% with a pass/fail criterion of 100,000 cm⁻³ was used. This is a very high failure rate and the emission of so many high polluters will dominate the emission of the whole fleet. Following this first findings a new instrument specification was discussed in order to improve reliability at low idle condition and simplify the instruments while minimizing the cost with the intention that even small workshops would use such instruments for vehicle checks. With these new generation instruments the fleet tests were repeated and the pass/fail criterion was lifted to 250,000 cm⁻³, resulting in failure rates of 8–10% for Euro 5 and 6–8% for Euro6 vehicles. Under the impression that these failure rates are far too high, the government of the Netherlands has decided to introduce this new PTI at low idle for all diesel vehicles in 2019 in government test centers and by the road police and make it mandatory for all workshops in 2021. The government of Belgium has decided to introduce immediately this test in the official GOCA centers and the government of Germany will make this test mandatory from January 2021. These decisions require a high number of instruments to be available by January 2021 and more than ten expert companies have joined the group and are now working on competitive solutions of this new type of instruments fulfilling the new instrument norm elaborated by the NPTI group and the Metrology Institute of the Netherlands NMI. Next steps on the policy side will be to extend this new PTI test to all European member states and also to states which are following the European emission legislation like China, Korea, India, Latin America and Canada. This is supported by the worldwide operating association for automotive control CITA, which is also partner of the N-PTI group. Summarized, also, are two posters presented by Andreas Mayer.

2.4.1. ECas toxic air contaminant is by far underestimated while NO₂ is overestimated

The Miners Study reports on eight US non-metal mining facilities (limestone, trona, potash and salt) of 12315 workers with respect to long-time Respirable Elemental Carbon (REC) exposure and found 198 lung cancer deaths, and a statistically overwhelming evidence that exposure to REC in diesel exhaust may cause lung cancer in humans [7].

Based on this finding, the World Health Organization (WHO) in 2012 moved diesel exhaust gas from class 3 to class 1, like asbestos. Using the usual number of a maximum of four deaths within a population of 100,000 as an acceptable guideline for a carcinogen in ambient air leads to a limit value of <0.1 µg/m³ for EC, as the NL-official OCR study concluded on October 26, 2017 [8]. There is not a limit value for Elemental Carbon (EC) in ambient air and in the working place in Switzerland, where EC is used to characterize diesel particle emissions, the actually valid limit value is 0.1 mg/m³ – 1000 times too high? Despite the WHO statement in 2012, no single government has adapted their limit values for PN. Adapting limit values for emissions and ambient air would permit to enforceable particle elimination strategies for the whole vehicle fleet, as well as other sources, within a short period. It is estimated that a reduction of 200,000 mortality cases in Europe would probably be possible within five years. NO₂ is also toxic and an irritating gas when inhaled by disabled persons and asthmatics. However, NO₂ is not carcinogenic and according to U.S.-EPA and other occupational health studies, it is not confirmed by any toxicity studies that NO₂ is responsible for mortality at concentrations below 400 g/m³. Most epidemiological cases cannot separate between the health effects of PN and NO₂. Today’s legal limit values are on the safe side; and the implemented emission reduction technologies as they are now required by European and US-Law will bring NO₂ concentration easily below the legally requested level. This could even be accelerated if the HD-fleet (Heavy Duty vehicle fleet) in cities would be retrofitted with S-DPF technology (stands for the combination of de-NO_x SCR technology by adblue and Diesel Particle Filter in one unit, where the SCR catalyst is coated on the DPF) [8], the combination of filter and de-NO_x catalysis, which is readily available. This strategy to upgrade the existing HD fleet by S-DPF retrofit will permit another big step in emission reduction while at the same time CO₂ and other short living global air warming substances will reduced.

2.4.2. Uniform metrics for toxic air contaminants are required to link vehicle emissions, air quality criteria and the working place

Ambient air in urban environments contains many kinds of particles and other toxic substances: natural and manmade, solid and volatile, soluble and insoluble. Some are ultrafine and some – by far, not all are highly toxic. Researchers have to discriminate, detect the sources of the most dangerous ones, and eliminate them by setting the correct metrics, monitor correctly, and use best available technology for mitigation measures for each of them. Health research has concluded that particle size is very important for lung uptake and organ translocation and has pinpointed engine emitted particles since they are nanosize, rather insoluble, coated with PAH and metals, and appear in high concentrations WHO has classified diesel engine exhaust “carcinogenic class 1”. Even at very high concentration (PN > 10⁶ particles/cc or 10¹⁴ particles/km respectively), these engines emitted solid particles in the size range of 10–300 nm however contribute very little to particle mass PM. Therefore a more sensitive metric for vehicle homologation and control of modern engines was needed; this was successfully completed with Euro VI and NRMM in Europe, not in the US. This inhibits comparison of engine emission quality between Europe and the US. In addition, ambient air quality control is lagging behind with outdated definitions, like PM₁₀ and PM_2.5, which fail to account for the importance of particle size or varying toxicity of contained substances. Differences in definitions of criteria pollution and a lack of limits for highly toxic trace elements like dioxins, furans, PAH and Nitro PAH, along with differences in measurement protocols exist. This anachronistic discrepancy is not only misleading the health effect research but also policy makers and the industry.

2.5. Will Northrop

Will Northrop (University of Minnesota – Twin Cities, Minneapolis, MN) and coworkers studied how dicarboxylic acids assist in the formation of atmospheric secondary organic aerosols (SOAs) through various mechanisms. SOAs influence weather patterns and affect human exposure to harmful pollutants. Few studies have directly linked dicarboxylic acid emissions to primary sources, such as internal combustion engines. Furthermore, previous studies were conducted with now decades-old vehicles which were unequipped with catalytic emissions control devices that are ubiquitous today. In recent work, they showed that dicarboxylic acids were present in the exhaust of a modern aftertreatment system (ATS) equipped diesel engine used in passenger vehicle applications [9]. In the current work, they sought to determine if dicarboxylic acids were also present in the exhaust from a modern gasoline direct injection (GDI) engine equipped with a catalytic gasoline particulate filter (GPF). Unlike the results from their study with the modern diesel engine, all dicarboxylic acid concentrations from the GDI engine were below the limit of quantification. It is unclear if these acids were not produced by the GDI engine tested, or if they were simply in insufficient quantity to be detected. Current work is looking to increase quantification sensitivity to determine the level of acid emissions from modern GDI engines. A second round of testing is currently underway to elucidate whether dicarboxylic acids are emitted from modern GDI engines. This includes increasing exhaust loading rates on filters and concentrating samples for GC-MS analysis.

2.6. Goruck Soubans

Goruck Soubans (Ph.D. candidate at Murdoch University) investigated the combustion by products from mixed sources in Perth, Western Australia through the development of small sampling packages that can be used at any location on the ground or can be attached to a small drone for aerial sampling. One package has a sorbent tube collecting volatile organic compounds (VOCs) that can be post-analysed by GCMS and another package with a 5-wavelength aethalometer that measures light absorbing carbons (LACs) directly. Measurement of air pollutants near one source in an area of several mixed sources do not normally represent the combustion by-products composition profile of that source due to reactions by atmospheric processes and mixing of emissions from surrounding sources. Qualitative results from VOC samples acquired so far reveal high concentrations of benzene, toluenee, ethylbenzene, and xylene (BTEX) VOCs near major roadways with more diverse kinds of VOCs near industrial areas. As for LACs, black carbon concentration in metropolitan parks reaches around 300 ng/m³ (a known background concentration value for ambient air) while near a coal power plant and oil refinery in an industrial area, it reaches around 4000 ng/m³. Near the latter combustion sources, absorption at 375 nm was easily noticed to be higher than at 880 nm showing the presence of brown carbon. Through extensive sampling of pollutants at various locations using the measuring techniques developed, and employing mathematical techniques including positive matrix factorisation to interpret the data gathered, the detected profiles of selected pollutants may pinpoint the specific categories of emission sources, i.e., transport and individual stationary combustion operations for better pollution control. The methodologies are also being developed as part of a wider project that seeks to investigate into emission from mining activities, for which NO_x measuring methods for aerial sampling have been also developed.

2.7. Kamaljeet Kaur

Kamaljeet Kaur (Ph.D. candidate, University of Utah) highlights the importance of combustion particle size and its effects on pathologically important responses in immune cells, specifically THP-1 cells, (differentiated into macrophage cells). She discussed the need to have the same chemical composition and significant differences in particle size distribution when performing studies to examine the relative importance of particle size. The different chemical composition of ambient PM fractions poses difficulties in resolving the effect solely of particle size on cellular response. The issue was addressed by using particles with consistent chemical composition, obtained by controlled combustion of a jet-fuel surrogate in a flat flame burner. The collected particles were resuspended in deionized water (DI) water, which was then fractionated into three size fractions using a differential centrifugation method. The three size fractions exhibited similar chemical characteristics (as confirmed by GC-MS) and substantially different particle size distributions. The smallest fraction had the greatest particle number concentration and surface area per unit mass, which is potentially responsible for the greatest cellular response by these smaller particles. At the same mass dose, the fraction with smallest sized particles induced the greatest oxidative potential, inflammatory response (TNFα), and early apoptosis compared to the other two fractions. This study concludes that for a similar mass concentration, the smallest particles pose a greater health risk than bigger particles. These results support previous studies suggesting that the delivered total surface area of particulate matter is a more important indicator of cellular response than particle mass or particle count. This finding may have implications for regulations of particulate matter emissions and measurements. Since combustion particles are complex in nature i.e. different sizes, shapes, and chemical compositions; they will, next, be exploring the effect of other potentially relevant physicochemical properties (i.e. shape and chemical composition) on cellular responses.

2.8. Ralf Zimmermann

Dr. Zimmermann and colleagues (UR and HMGU: University of Rostock (UR) and Helmholtz Zentrum München, Photonion GmbH, and the UEF: University of Eastern Finland worked together within the HICE Helmholtz Virtual Institute) investigated the impact of atmospheric aging on composition and toxicological potential of combustion emissions. Wood combustion emissions (using state of the art residential wood stove) are photochemically aged in a new, innovative flow tube reactor (PEAR). Fresh and aged emissions were characterized and subjected to human and murine lung cell cultures at the air-liquid interface. Also animals were exposed (3 × 4 h exposures). The biological response of the cell cultures and mice samples to the exposure subsequently was investigated (cytotoxicity, viability, genotoxicity, transcriptome analysis). The organic composition was investigated by analysis of filters using direct thermal desorption/derivatisation GC-MS and a novel instrumental method (developed at UR), which hyphenates thermal optical carbon analysis (TOCA) and photoionization mass spectrometry (PIMS). Wood combustion effluents exhibit high concentration of genotoxic PAHs. Photochemical aging (simulated atmospherical aging time: 2 days) causes a substantial decrease of the PAH (by 80–90%). The organic mass, however, increases (SOA formation) [10]. Also some oxidized PAH are more abundant in the aged wood combustion aerosol. The human (A549) and murine (RAW264.7) lung cells showed increased cytotoxicity and reduced viability (metabolic activity) upon exposure to the aged wood combustion aerosol. The genotoxic responses (Comet assay) of lung cell cultures exposed to fresh and aged emissions were equally high, while in the animal data higher genotoxity was induced by the aged emissions. First transcriptome results suggest that different mechanisms resulted in the observed genotoxic effects. In general the gas phase appeared to play an important role in the observed enhanced toxic effects of aged combustion aerosols. The results show how complex the changes are upon aerosols aging in the atmosphere and make clear that atmospheric aging matters. The results also show that too little is known about the detoxification and potential toxification of emissions in the atmosphere. Highly interdisciplinary research programs are required to fill the knowledge gaps and new instrumental analysis techniques as well as biological test system need to be developed to better understand the effects of air pollution in the atmosphere on human health. Next experiments will address anthropogenic and biogenic SOA as well the impact of seed particles and are currently performed in the framework of the recently funded Helmholtz International Laboratory aeroHEALTH (www.aerohealth.eu, a joint initiative of the Helmholtz Zentrum München, Germany; the Weizmann Institute of Science, Israel and the Forschungszentrum Jülich, Germany).

3. Open fires

The open fires sessions were chaired by Brian Gullett (U.S. EPA/ORD) and M.I. Gilmour (U.S. EPA/ORD). The plenary lecture, summarized below, was given by David M. DeMarini (U.S. EPA/ORD).

David DeMarini (U.S. Environmental Protection Agency, Research Triangle Park, North Carolina) gave an overview of 40 years of research at the U.S. EPA/RTP on the (1) mutagenicity emission factors for the open burning of plastic, wood, tires, and oil and (2) urinary mutagenicity resulting from opening burning among charcoal producers and firefighters. Using the Salmonella (Ames) mutagenicity assay, EPA researchers have determined the mutagenicity emission factors, expressed as revertants/megajoulethermal (rev/MJth) for a wide variety of combustion emissions. A revertant is a mutant bacterial colony, which can be induced by extractable organic material (EOM) from the particulate matter (PM) of the emissions. This research group found that the mutagenic potencies of the EOM from the PM from dozens of combustion emissions span three orders of magnitude, as do the carcinogenic potencies of these EOMs on mouse skin [11]. There is a high correlation (r > 0.9) between the carcinogenic potencies of these EOMs in mice and the risk for lung cancer in humans based on epidemiology [12]. Mutagenicity emission values range over 6 orders of magnitude, with emissions from utility boilers combusting natural gas being the lowest (10 rev/MJth) to those from the open burning of tires being the highest (> 10⁶ rev/MJth) [13], [14], [15]. The rev/MJth values for the open burning of wood, crude oil, plastic, or tires are 5–6 orders of magnitude greater than those for controlled combustion, such as utility boilers combusting natural gas or coal. Diesel exhaust and biomassburning cookstoves have rev/MJth values that are intermediate to those of open burning and highly controlled burning [16], [17]. With few exceptions, these data generally show that how materials are burned (open or controlled burning) rather than what materials are burned is the most critical factor influencing the mutagenicity emission factor. Human exposure to combustion emissions, especially from open burning, can result in systemic exposures to mutagens and the induction of a variety of genotoxicity biomarkers [18], such as urinary mutagenicity [19], [20], and can cause cancer [21]. These data can help support policy decisions regarding the health effects of open burning and air pollution resulting from combustion emissions.

3.1. Veronica Kimmerly

Veronica Kimmerly (PhD student in Fire Protection Engineering at Worcester Polytechnic Institute) aims to determine the effects of geometry on open fires, particularly the effects of placing the fire in a pit as is commonly done when burning waste. Fire remains the most effective means of reducing the volume of solid waste and open air fires are commonly used in low-infrastructure areas to dispose of waste. Pits are used as an easy way to collect the waste in one location and to limit the fire spread to adjacent buildings or people. Experiments were conducted in a 10 cm by 10 cm square pit with a methane gas burner to determine the effect of pit depth (ullage) on oxygen consumption, carbon monoxide and carbon dioxide generation, air entrainment rates, and flame pulsation. A novel flame shape was observed once a critical pit depth was reached, where, the flame began to open-up in the center into two or more distinct branches and close back into a conical shape at a quantifiable frequency. This opening and closing behavior of the flame changes the air entrainment such that partial premixing is promoted and at a certain pit depth a region of low frequency pulsations results in a reduction in the carbon monoxide/carbon dioxide ratio and increasing the burning efficiency. These results offer a simple method for reducing the hazard of open air burning of waste in pits by controlling the ullage of the pit. Current methods for improving these waste fires are often too costly or infrastructure intensive to be adopted in the areas where they are most needed. A computational fluid dynamics model of a circular pit is being developed and will be validated against experimental results collected from further benchtop scale testing. A mesoscale, approximately 50 cm diameter, experiment with liquid fuels is planned for the spring of 2020. Furthermore, a transition to more realistic solid fuels is being planned.

4. Indoor air pollution

This session was chaired by Andre Boehman (University of Michigan) and C. Rider. The plenary lecture was given by Lupita Montoya, from the University of Colorado Boulder, on the “Challenges in controlling indoor air pollution and improving health in underserved and developing communities”. There were several presentations on indoor air pollution, some of which are summarized in this section of the article.

Eric Vejerano (Environmental Nanoscience in Air Quality Lab, University of South Carolina) described his ongoing research on measuring the gas-to-particle partitioning constant (Kp) of volatile organic compounds (VOCs) as a function of the VOC’s chemical composition, aerosol composition, relative humidity (RH), and temperature. Although VOCs exist mainly in the gas phase rather than in aerosols, the mass fraction of VOCs measured in aerosols are comparable to those of semi-volatile organic compounds, which preferentially partition into aerosols. In this study, the team measured the Kp for representative VOCs into an organic aerosol (succinic acid) and inorganic aerosol (ammonium sulfate) in a preciselycontrolled environmental chamber under varying levels of RH and temperature. To determine the impact of chemical polarity on partitioning, n-Butanol (n-BuOH), 1,2-dichlorobenzene (1,2-DCB), and trichloroethylene (TCE) were used as representatives of polar, moderately polar, and non-polar VOCs, respectively. For both aerosol composition, Kp for TCE was two orders of magnitudes lower (10⁻¹³) than for 1,2-DCB (10⁻¹¹) while the Kp for n-BuOH (10–8) was three orders of magnitude higher than for 1,2-DCB. For organic and inorganic aerosols, Kp decreased with RH and decreased with temperature. At low RH, VOCs interacted with ammonium sulfate aerosol possibly on sorbed layers of molecular water via Van der Waal (VdW) interactions. At high levels of RH, water solvated the dissolved ions, reducing the uptake of VOCs, and reducing the sites for VdW interactions. At low levels of RH, molecular layers of water on succinic acid aerosol may have enhanced hydrogen-bonding resulting in an increase in Kp. But at high levels of RH, competitive interactions occur in which succinic acid aerosol preferentially sorbed water than n-BuOH. Also, Kp of VOCs sorbing on succinic acid aerosols were less sensitive to the levels of RH compared to those on ammonium sulfate aerosols. △H_des values were lower than the VOC’s △H_vap except for n-BuOH on ammonium sulfate aerosols. n-BuOH and TCE exhibited similar behavior as 1,2-DCB. Estimate of thermal desorption energy for 1,2-DCB was 39–128 kJ/mol, which are higher than the enthalpy of vaporization for the pure compounds. These results are important in determining the impact of VOCs on aerosols undergoing atmospheric processing. Also, results will enable a more accurate assessment of the health impact of VOCs that are sorbed on aerosols as their health effects vary from those exerted by the pure aerosol or by the VOC alone.

4.1. Alexandra Noël

Alexandra Noël (Department of Comparative Biomedical Sciences at Louisiana State University, Baton Rouge, LA) studied the effects of in utero exposure to second-hand smoke (SHS), a major indoor pollutant in the homes of smokers, on adult lung gene and protein expression in SHS-associated lung diseases. Matrix metalloproteinase 12 (Mmp12) protein and gene expression, as well as the associated extracellular matrix remodeling, were assessed following induction of 3 distinct smoke-associated lung diseases in lungs of adult mice that had been exposed only in utero to SHS. In utero, SHS exposure alone up-regulated the lung Mmp12 protein expression by 2.4-fold in 15-week old mice; in an adult elastase-induced emphysema model, in utero SHS exposure yielded enlarged lung airspaces and increased Mmp12 gene expression by 10.3-fold; in a house dust mite asthma model, in utero SHS aggravated the asthma phenotype, accompanied by an 8.3 fold up-regulation of the Mmp12 expression in the lungs; and in an urethaneinduced lung cancer model, in utero SHS exposures led to a 9.3-fold increase in the lungs expression of Mmp12 gene in 1 year-old mice. These results strongly suggest that up-regulation of Mmp12 lung gene expression is central to development of in utero SHS-aggravated adult lung diseases. Next steps would involve the confirmation of Mmp12 roles in utero SHS exposures using Mmp12 knockout (KO) mice.

4.2. Esra Mutlu

Esra Mutlu (Division of the National Toxicology Program [22], National Institute of Environmental Health Sciences, RTP, NC) presented NTP’s efforts to investigate the stability of cookstove filters. The effects of storage and length on stability was evaluated by two commonly used endpoints, extractable organic material (EOMs) and polycyclic aromatic compounds (PACs) levels in the extracts of filters. In collaboration with RTI International and US EPA, low-moisture red oak was burned in a natural draft stove by mimicking field conditions (uncontrolled burn) and laboratory conditions (controlled burn) and PM2.5 was collected on PTFE Teflon filters. Filters were stored at ambient temperature and −20^◦C for 1-, 7-, 30-, and 90-days, and extracted with dichloromethane. Percent EOM in extracts was estimated by gravimetric methods. Data were analyzed using a two-way ANOVA model with fixed effects for storage time and temperature. Results show an interaction effect between the time and temperature variables; the effect of storage temperature differs between times only under the laboratory condition while no statistical difference was found under the field condition. These findings suggested that EOM alone shouldn’t be used as an indication of instability. Therefore, extracts were further analyzed by GC/MS-TIC, 2D-GC, and GC/MSD-SIM to evaluate non-targeted chemical profiles of the extract and PAC levels in the extracts. Selected 22 PACs (16 EPA PAHs and NTP PACs1) were monitored to determine similarities and/or differences between different conditions. Based on the sensitivity required, GC/MSD-SIM was chosen to analyze the cookstove extracts. Total of 22 PACs will be quantified to understand the effect of burn and storage conditions on stability. Future studies will include evaluating the correlation between chemistry and biology will be evaluated by in vitro testing of extracts generated from the controlled and uncontrolled burns.

5. Halogenated Pollutants

The plenary talk in this session was given by Dr. Richard Di Giulio on the “Effects of PAHs on Development in Fish and Evolutionary Consequences”. His talk focused on the Elizabeth River system, an estuary in southeastern Virginia, USA, surrounded by the towns of Chesapeake, Norfolk, Portsmouth, and Virginia Beach. The river has played important roles in U.S. history and has been the location of various military and industrial activities. These activities have been the source of chemical contamination in this aquatic system. Important industries, until the 1990s, included wood treatment plants that used creosote, a petroleum-derived product that is rich in polycyclic aromatic hydrocarbons (PAHs). These plants left a legacy of PAH pollution in the river and in particular Atlantic Wood Industries is a designated Superfund site now undergoing remediation. This presentation focuses on how a small estuarine fish with a limited home range, Fundulus heteroclitus (Atlantic killifish or mummichog) has responded to this pollution. While in certain areas of the river, this species has clearly been impacted as evidenced by elevated rates of liver cancer, some subpopulations, notably the one associated with the Atlantic Wood Industries site, display a remarkable ability to resist the marked effects PAH have on the embryonic development. This presentation will highlight studies demonstrating the heritability of this resistance and associated fitness costs, as well as mechanisms underlying resistance and the effects of PAHs on cardiovascular development in non-adapted fish. It concludes with a description of ongoing and promising efforts to restore this historic American river.

The second session on “Halogenated Pollutants”, held on July 11th, 2019, was chaired by Dr. Stina Jansson from Umeå University, Sweden. The keynote speaker was Dr. Heidelore Fiedler (Orebro University, Sweden), who opened the session by a plenary talk entitled Dioxins and other unintentional POPs under the Stockholm Convention. Fiedler provided a background to the Stockholm Convention on Persistent Organic Pollutants (POPs), which entered into force in 2004, and gave an overview to the POPs listed in the different annexes. For the unintentionally formed compounds, listed in annex C, parties to the Stockholm Convention are required to develop release inventories and update them every five years. Although reporting is not complete and there is no one reference year, there is quite comprehensive information as to the release inventories for polychlorinated dibenzo-p-dioxins (PCDDs) and dibenzofurans (PCDFs), but information for other unintentional POPs is scarce.

Fiedler also gave examples of release inventories from different countries, and how the Toolkit for Identification and Quantification of Releases of Dioxins, Furans and Other Unintentional POPs provided by United Nations Environment Programme (UNEP) is applied to generate an estimated POPs emission inventory. The toolkit is intended to assist parties in establishing release inventories of unintentional POPs that are consistent in format and content, that are comparable and that can allow identification of priorities and follow changes over time at national, regional and global level. A crucial part of the development of the toolkit was establishing emission factors (EFs) for all source categories, based on available data in the cases where such data existed, and based on dedicated experimental campaigns to provide EFs or source categories with insufficient data for establishing EFs. Results from global PCDD and PCDF release inventories showed that the highest emissions originated from China and India, and with releases per country indicating open burning as the dominating source category.

5.1. Ibukun Oluwoye

Ibukun Oluwoye (Discipline of Chemistry and Physics, Murdoch University, Australia) investigated the formation of solid nitrogenated by-products in biomass reburning, a process for mitigating oxides of nitrogen (NOx) in stationary combustion plants. The experimental approach involved isothermal high-temperature experiments in a vertically-entrained reactor, and in situ diffuse reflective infrared Fourier transform spectroscopy (DRIFTS) under a non-isothermal heating conditions. Results from this study elucidate the formation of nitrated structures as active intermediate species of the heterogeneous reaction of biomass and NOx. The nitrogenated signatures persist on the surface of the residual ash, suggesting the production of N-aromatics such as nitro-PAH. Considering the severe toxicity and bioaccumulative properties of these by-products, further research should focus on the relative contribution of various reburning fuels, while favouring sustainable fuels such as not-charring plastics.

5.2. Xiaodong Li

Xiaodong Li of Zhejiang University, China, presented a study on PCDD/F and PCB from circulating fluidized bed (CFB) municipal solid waste (MSW) incinerators. Because of the high moisture content and low heating value, CFB incinerators have been widely adopted in China for incinerating MSW since 1998. Two typical CFB incineration plants (referred to as Plants A and B) were investigated for concentrations and fingerprints of PCDD/F and PCB at different positions downstream the post-combustion zone, aiming to draw a full picture of their formation and distribution. For both plants, the load of PCDD/F and dioxinlike PCB in ashes also amplified steadily with reduced temperatures of the flue gas. In Plant A, a continuous increase in PCDD/F and PCB levels in the flue gas was observed from the superheater to the inlet of the air pollution control system, with the most notable rise observed at the air preheater. The main formation of PCDD/Fs in the CFB plants was attributed to heterogeneous catalytic pathways. PCB concentrations were found to be approximately one order of magnitude higher than the PCDD/F concentrations, and dominated by homologues with a lower degree of chlorination compared to the PCDD/Fs.

5.3. Shengyoung Lu

Shengyoung Lu (Zhejiang University, China) presented work on the development of a novel and highly efficient adsorbent for removal of organic pollutants from coal-combustion flue gas. With increased economical development and environmental protection awareness, more pollutants need be controlled from coal-combustion flue gas.

To address this need, Lu and co-workers proposed and evaluated the efficiency of a biomass-derived carbon material as a sorbent material. The carbon material was generated from biomass as carbon precursor and ammonium oxalate as both nitrogen source and foaming agent, which provided the carbon material with a large surface area, excellent hierarchical nanostructure and abundant nitrogen-containing functional groups. Compared with conventional activatedcarbon, the hierarchical porous carbon showed highly efficient absorption and faster adsorption kinetics of coal-combustion organic pollutants such as toluene and chlorobenzenes. Further investigations indicated that the interconnected porous structure and nitrogen-containing functional groups contributed to the improved diffusion and mass transfer, which in turn contributed to its considerable adsorption performance. Based on the facile preparation process and high adsorption capacity, the biomass-derived hierarchical porous carbon could have promising widespread applications in removing organic pollutants from coalcombustion flue gas. The next work plan is to explore industrial production methods for the hierarchical porous carbon, realize its commercial application as soon as possible.

5.4. Ibukun Oluwoye

Ibukun Oluwoye (Discipline of Chemistry and Physics, Murdoch University, Australia) concluded the session with a study of the destruction of PCDDs and PCDFs via electrophilic attack of singlet oxygen. They focused on identifying reactions that allow destruction at low temperatures using the nature of the singlet oxygen, using density functional theory. The study elucidated the thermodynamic and kinetic feasibility of singlet oxygen-assisted oxidation of polycyclic and halogenated aromatic hydrocarbons. For both PCDD and PCDF, dioxetane products were generated via diradical intermediate channels with enthalpic requirements of the initial reactions being relatively small at around 100 kJ/mol, as compared to those overcame in high-temperature incineration by ground-state molecular oxygen. Moreover, the supplementary Diels-Alder reaction corridor appears inferior as the so-called ene reaction is impractical due to the absence of allylic hydrogen in the selected aromatic systems. These outcomes have practical implication in photo-oxidation and enhanced thermal incineration of halogenated waste products, and enhanced thermal destruction of dioxins and furans through the electrophilic attack of singlet oxygen should be instrumental in reducing the risk of exposure of these pollutants.

5.5. Stina Jansson

Stina Jansson (Umeå University, Sweden) presented a study on the influence of reactor type and operating conditions of the pyrolysis unit on the final concentration of toxic contaminants such as polycyclic aromatic hydrocarbons (PAHs) in biochar. The physical and chemical properties of biochars make them interesting for use in several different application areas, e.g. as a replacement or supplement to activated carbon in environmental or agricultural applications. But there may also be contaminants present in the biochars, such as PAHs, potentially toxic elements (PTEs), volatile organic compounds (VOCs), and even chlorinated aromatics. There is a relationship between the pyrolysis temperature and the concentration of PAH in biochar [23] but the influence of scale, reactor type, and configuration of the pyrolysis unit on concentrations of PAH and similar compounds in biochar has been unknown. The concentrations of PAHs, oxygenated polycyclic aromatic hydrocarbons (oxy-PAHs), nitrogen-containing polycyclic aromatic compounds (N-PACs), polychlorinated dibenzo-p-dioxins (PCDDs), and dibenzofurans (PCDFs) in biochars produced from three different feedstocks (softwood, wheat straw, and anaerobic digestate) in three pyrolysis units of different scale revealed that their presence were more dependent on feedstock than scale of the pyrolysis unit, and mainly found in the liquid fraction and not to the same degree in the biochars [24]. In all biochars, oxy-PAH and N-PAC concentrations were notably lower than PAH concentrations. Concentrations of PCDDs and PCDFs were almost negligible, both in biochars and in the liquids. With regard to these types of contaminants, the biochars assessed in this study represent a low risk to the environment based on threshold values set by IBI (International Biochar Initiative 2015)) for biochar used in soil.

6. Poster session

The poster session was held on the second day of the conference and awards were presented that evening to the three best posters. The poster committee evaluated all posters on their design, clarity of presentation – both visual and oral – and their scientific content. A total of 21 presenters participated in the poster session on a variety of subjects.

Jake Kovalic (undergraduate student) and Jacob Saldinger (PhD candidate) from the University of Michigan Angela Violi Lab, and Miles Burnett (PhD candidate) from the University of Michigan Margaret Wooldridge Lab were the three poster competition winners. Jacob Saldinger presented a poster, titled “Characterizing Aromatic Formation in a Coflow Diffusion Flame”. Jake Kovalic presented a poster, titled “Methane Thermal Decomposition: A Case Study For Density-Functional Tight-Binding Molecular Dynamics”. He used DFTB and metadynamics to create accurate free energy surfaces for a bond breaking in methane and compared it to previous ab initio results. Miles Burnett presented a poster, titled “An Experimental Investigation of Flame and Autoignition Behavior of Propane”.

7. Translating research and engaging communities

7.1. Jennifer K. Irving

Jennifer K. Irving (Louisiana State University) presented a retrospective analysis of research translation and community engagement activities from the Louisiana State University Superfund Research Center (LSU SRP). Ms. Irving discussed the Translational Research Framework for Environmental Health Science developed by NIEHS [25] to include additional fundamental questions for research in basic chemical science. The NIEHS framework is visually depicted as a series of concentric rings that represent five categories of research that progress from basic to applied: fundamental questions, application and synthesis, implementation and adjustment, practice and impact. Using the framework, they developed a translational research story for environmentally persistent free radicals (EPFRs), which are pollutant particle systems formed during thermal treatment processes [26]. The story included three translational bridges: applying the knowledge gained from observing EPFRs in the environment and studying them in the laboratory (fundamental questions) to develop a method for producing EPFRs for biomedical studies (application and synthesis); using laboratorygenerated EPFRs (application and synthesis) in biomedical studies to establish that EPFRs induce oxidative stress and impact cardiovascular, respiratory, and metabolic health (fundamental questions); and applying the knowledge gained about the formation and health effects of EPFRs (fundamental questions) to inform risk management (practice) and reduce/prevent exposure (impact) during the Camp Minden Superfund site remediation. The Camp Minden case-study is a reminder that not all impacts from basic research can be predicted: the explosions at Camp Minden due to the improper storage of over 16 million pounds of hazardous wastes and explosive materials, and the subsequent need for scientific expertise were unanticipated [27]. However, the structure of the LSU SRP, which includes planning for research translation and community engagement using tools like the adapted NIEHS translational research framework, facilitated the Center’s involvement in Camp Minden and, importantly, enabled the employment of a contained burn chamber, which significantly reduced the emitted hazardous wastes and associated health impacts.

7.2. Round table discussion

The PIC 2019 conference wrapped up with a panel discussion, focused on the topic of “Translating Research and Engaging Communities.” This topic is important in the application of all STEM disciplines, with the intention of acquiring the means to produce a tangible impact from research studies. A panel of six experts, in their respective fields, explored the significance of community engagement and translational research by answering a series of questions. The panel consisted of Andreas Mayer (Technik Termische Maschinen (TTM), Niederrohrdorf, Switzerland), Richard Guilio (Duke University), Heidelore Fiedler (Örebro University, Sweden), Lupita Montoya (University of Colorado Boulder), Nick Leonard (Executive Director at Great Lakes Environmental Law Center), and Andre Boehman (University of Michigan). The session was moderated by Danielle Carlin (National Institute of Environmental Health Sciences).

Prepared questions the panelists were asked to address, include:

• What prevention/intervention activities can be conducted or are currently available to achieve positive public health benefits, rather than the negative health effects that are typically associated with combustion by-products?

The discussion began with a general summary of the scope of the problem with exposure to combustion by-products. Some of the panelists were quoted as saying, “2% of vehicles are responsible for 95% of the pollutant emissions in Mexico City” and, “10% of the cars in the U.S. emit half of the emissions”. Thus, this demonstrates how vehicular pollution is a significant contributor to total pollutant emissions and further that only a small number of vehicles contribute a large amount of combustion by-products. The next part of the discussion questioned what can experts do to reduce these emissions. Some specific examples that were mentioned included electrification and filters, the use of natural gas, and altering the view of the general public to not only recognize vehicles on land as a pollution issue, but to move the issue to encompass land, water, and air vehicles. In addition, the panel indicated that it is important to realize that when developing solutions to old problems, they can, in the process, introduce new issues/complications that require their own sets of solutions. From a policy standpoint, policy-makers can become more diligent in their role/responsibility to legislate limiting human exposure and being conscious about where new construction is occurring and may be emitting combustion by-products (e.g., buildings, highways, etc.). Of these ideas to improve public health, the most easily-implementable solutions are considered to be (1) educating and working with communities/countries resisting or ignoring the inevitability that climate change will affect combustion by-product production and prevention; (2) assuring the public that researchers are looking for solutions; and (3) highlighting successful solutions.

• What activities can be accomplished to promote bidirectional interactions among combustion by-products, researchers, and impacted communities?

The panelists unanimously agreed that improvement to public health and safety from combustion by-products is needed. To promote bidirectional interactions, one suggestion was for researchers to be active listeners when meeting with communities. This was thought to be one of the best ways to show communities that you care and want to build a relationship. In addition, researchers are interested in community engagement needed to understand the cultural environments of the communities that they are engaging and should learn to leverage community members from different cultures and experiences.

• How can combustion by-product experts to a better job at explaining the risk of combustion by-products to a community’s health, especially when countries vary in their federal standards for vehicles, power plants, etc.?

The panelists agreed that academics and researchers have a responsibility to share their research and indicate to companies, the public, and communities when health effects are occurring because of combustion by products.

One concept that was up for debate was the extent to which various community groups should be involved in policy-making and the solution development process. Some of the panelists advocated for full community engagement, while others were more reserved by their indication that involving more people may, ultimately, slow the timeline for change and risk valuing the opinions of individuals over the group.

The panelists agreed that different areas of expertise are going to disagree at times, but when communicating to broader audiences, they should maintain their focus and stay on a chosen path. In addition, they agreed that no one has the right to pollute and that we all have to be responsible for our own actions. As scientists, we have an ethical duty to engage with our communities regarding the implications of combustion by-product pollution. There is still much to discuss and solutions that haven’t yet been considered.