Michael D. Hays

Pollutant Emissions and Energy Efficiency under Controlled Conditions for Household Biomass Cookstoves and Implications for Metrics Useful in Setting International Test Standards

Realistic metrics and methods for testing household biomass cookstoves are required to develop standards needed by international policy makers, donors, and investors. Application of consistent test practices allows emissions and energy efficiency performance to be benchmarked and enables meaningful comparisons among traditional and advanced stove types. In this study, 22 cookstoves burning six fuel types (wood, charcoal, pellets, corn cobs, rice hulls, and plant oil) at two fuel moisture levels were examined under laboratory-controlled operating conditions as outlined in the Water Boiling Test (WBT) protocol, Version 4. Pollutant emissions (carbon dioxide, carbon monoxide, methane, total hydrocarbons, and ultrafine particles) were continuously monitored. Fine particle mass was measured gravimetrically for each WBT phase. Additional measurements included cookstove power, energy efficiency, and fuel use. Emission factors are given on the basis of fuel energy, cooking energy, fuel mass, time, and cooking task or activity. The lowest PM(2.5) emissions were 74 mg MJ(delivered)(-1) from a technologically advanced cookstove compared with 700-1400 mg MJ(delivered)(-1) from the base-case open 3-stone cookfire. The highest thermal efficiency was 53% compared with 14-15% for the 3-stone cookfire. Based on these laboratory-controlled test results and observations, recommendations for developing potentially useful metrics for setting international standards are suggested.

Polycyclic aromatic hydrocarbon size distributions in aerosols from appliances of residential wood combustion as determined by direct thermal desorption—GC/MS

In this work, a direct thermal desorption/gas chromatography/mass spectrometry (TD/GC/MS) method is implemented to determine the polycyclic aromatic hydrocarbon (PAH) composition in size-segregated aerosols from residential wood combustion. Six combustion tests are performed with two commonly burned wood fuel species, Douglas-fir (Pseudotsuga sp.) and white oak (Quercus sp.). Atmospheric dilution and cooling of the aerosol plume are simulated in a newly designed wind tunnel, and the resulting aerosols are size classified with an electrical low-pressure impactor (ELPI). ELPI stage data speciated by TD/GC/MS were inverted and modeled using a log normal distribution function. Gravimetrically determined PM2.5 (fine particles with aerodynamic diameters ) emission rates (2.3–) corroborate to matrix-corrected ELPI mass measurements of stages 1–8 (2.7–). Fuel moisture content linearly correlates (r2=0.986) to the PM2.5 mass geometric mean diameter (dg). Combustion efficiency (CO2/CO) and temperature, O2 levels, and gas dilution temperature affect particle size distributions; dg ranges from 313 to , indicating an accumulation mode. Reconstruction and summation of inverted ELPI data allow for the quantification of 27 individual PAHs (and clusters of structural PAH isomers); PAHs characterize between 0.01 and of the PM2.5 mass. Benzo[a]pyrene predominates the PAH emissions. PAH size allocations (dg are out of phase with PM2.5 mass ones and shifted to finer da. Higher and lower MW PAHs preferentially segregate to fine and coarse da in that order. The ultrafine mode contains on average greater than 80% of the total measured particle number concentration. Values of dg for particulate matter surface area distributions are between 120 and . For these tests, PAH mass and PM surface area linearly correlate (r2⩾0.913). Application of a simple function to consider adsorption and absorption mechanisms makes apparent that (a) surface and core compositions of PAH of identical MW groups vary with combustion and (b) preferential surface adsorption of lower MW PAH is possible.

The application of thermal methods for determining chemical composition of carbonaceous aerosols: a review.

Thermal methods of various forms have been used to quantify carbonaceous materials. Thermal/optical carbon analysis provides measurements of organic and elemental carbon concentrations as well as fractions evolving at specific temperatures in ambient and source aerosols. Detection of thermally desorbed organic compounds with thermal desorption-gas chromatography/mass spectrometry (TD-GC/MS) identifies and quantifies over 100 individual organic compounds in particulate matter (PM) samples. The resulting mass spectra contain information that is consistent among, but different between, source emissions even in the absence of association with specific organic compounds. TD-GC/MS is a demonstrated alternative to solvent extraction for many organic compounds and can be applied to samples from existing networks. It is amenable to field-deployable instruments capable of measuring organic aerosol composition in near real-time. In this review, thermal stability of organic compounds is related to chemical structures, providing a basis for understanding thermochemical properties of carbonaceous aerosols. Recent advances in thermal methods applied to determine aerosol chemical compositions are summarized and their potential for uncovering aerosol chemistry are evaluated. Current limitations and future research needs of the thermal methods are included.

Traffic and Meteorological Impacts on Near-Road Air Quality: Summary of Methods and Trends from the Raleigh Near- Road Study

Abstract 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.

PCDD/F, PCB, HxCBz, PAH, and PM Emission Factors for Fireplace and Woodstove Combustion in the San Francisco Bay Region

Emissions from residential fireplace and woodstove appliances burning fuels available from the San Francisco Bay area were sampled for polychlorinated dibenzodioxins and dibenzofurans (PCDDs/Fs), polychlorinated biphenyls (PCBs), hexachlorobenzene (HxCBz), particulate matter (PM), polycyclic aromatic hydrocarbons (PAHs), oxygenated PAHs, and the monosaccharide levoglucosan. Emission factors for these pollutants were determined, the first known characterization of this extent. Common California natural firewoods and manufactured artificial logs were tested under operating conditions intended to reflect domestic use patterns in the Bay area, which are primarily episodic burning for aesthetic reasons. Emission factors were determined by fuel type, fuel weight, mass emission rates, and energy output, highlighting differences between fuel and combustion facility type. Average PCDD/F emissions factors ranged from 0.25 to 1.4 ng toxic equivalency (TEQ)/kg of wood burned for natural wood fuels and 2.4 ng TEQ/kg f...

XPS analysis of combustion aerosols for chemical composition, surface chemistry, and carbon chemical state.

Carbonaceous aerosols can vary in elemental content, surface chemistry, and carbon nano-structure. Each of these properties is related to the details of soot formation. Fuel source, combustion process (affecting formation and growth conditions), and postcombustion exhaust where oxidation occurs all contribute to the physical structure and surface chemistry of soot. Traditionally such physical and chemical parameters have been measured separately by various techniques. Presented here is the unified measurement of these characteristics using X-ray photoelectron spectroscopy (XPS). In the present study, XPS is applied to combustion soot collected from a diesel engine (running biodiesel and pump-grade fuels); jet engine; and institutional, plant, and residential oil-fired boilers. Elemental composition is mapped by a survey scan over a broad energy range. Surface chemistry and carbon nanostructure are quantified by deconvolution of high-resolution scans over the C1s region. This combination of parameters forms a distinct matrix of identifiers for the soots from these sources.

Chemical characterization of the fine particle emissions from commercial aircraft engines during the Aircraft Particle Emissions eXperiment (APEX) 1 to 3.

This paper addresses the need for detailed chemical information on the fine particulate matter (PM) generated by commercial aviation engines. The exhaust plumes of seven turbofan engine models were sampled as part of the three test campaigns of the Aircraft Particle Emissions eXperiment (APEX). In these experiments, continuous measurements of black carbon (BC) and particle surface-bound polycyclic aromatic compounds (PAHs) were conducted. In addition, time-integrated sampling was performed for bulk elemental composition, water-soluble ions, organic and elemental carbon (OC and EC), and trace semivolatile organic compounds (SVOCs). The continuous BC and PAH monitoring showed a characteristic U-shaped curve of the emission index (EI or mass of pollutant/mass of fuel burned) vs fuel flow for the turbofan engines tested. The time-integrated EIs for both elemental composition and water-soluble ions were heavily dominated by sulfur and SO(4)(2-), respectively, with a ∼2.4% median conversion of fuel S(IV) to particle S(VI). The corrected OC and EC emission indices obtained in this study ranged from 37 to 83 mg/kg and 21 to 275 mg/kg, respectively, with the EC/OC ratio ranging from ∼0.3 to 7 depending on engine type and test conditions. Finally, the particle SVOC EIs varied by as much as 2 orders of magnitude with distinct variations in chemical composition observed for different engine types and operating conditions.

Thermal extraction–two-dimensional gas chromatography–mass spectrometry with heart-cutting for nitrogen heterocyclics in biomass burning aerosols

A thermal extraction-two-dimensional gas chromatography-mass spectrometry (TE-GC-GC-MS) method with heart-cutting is developed for quantitatively assessing nitrogen (N)-bearing organic species (e.g., pyrrole, pyridine, nitriles, and amines) in aerosols emitted from agricultural fires. Pyrolysis of the constituents in the crop residue is a likely formation pathway for these compounds. An evaluation of the TE-GC-GC-MS method proficiency for them confirms low carryover (<1%), adequate recovery (84-100%), high reproducibility (<9% RSD), picogram method detection limits, and a linear dynamic range spanning four orders of magnitude. The 14 substances for which quantitative results are available are primarily heterocyclic aromatic N compounds that comprise 0.7% (w/w) of the total fine aerosol mass. The benefits of TE-GC-GC-MS versus conventional GC-MS methods for organic N species in aerosols may depend on the matrix and the target N analyte concentration in that matrix; for the biomass burning aerosol examined in this study, the former approach reduces the unresolved complex mixture and detects organic N species not seen with GC-MS. We show another advantage of TE-GC-GC-MS is that it adequately resolves the anhydro-sugar (e.g., levoglucosan), alkanoic acid, and substituted phenol molecules in the biomass burning aerosol without the use of methylation or trimethyl-silyl derivatizing agents.

Differences in the OC/EC Ratios that Characterize Ambient and Source Aerosols due to Thermal-Optical Analysis

Different thermal-optical methods used to measure OC/EC and EC/TC ratios in atmospheric aerosols often produce significantly different results due to variations within the temperature programming and optical techniques of each method. To quantify the thermal and optical effects on these ratios, various source (residential cookstoves and diesel exhaust) and atmospheric (rural and urban) aerosols were analyzed using 3 thermal protocols: (1) two modified versions of the Birch and Cary (1996, Elemental Carbon-Based Method for Monitoring Occupational Exposures to Particulate Diesel Exhaust. Aerosol Sci. Technol., 25:221–241) National Institute of Occupational Safety and Health (NIOSH 5040) protocol—designated in this paper as NIOSH and NIST-EPA protocols, and (2) the IMPROVE (the Interagency Monitoring of Protected Visual Environments) protocol outlined by Chow et al. 1993 (The DRI Thermal/Optical Reflectance Carbon Analysis System: Description, Evaluation, and Applications in U.S. Air Quality Studies. Atmos. Environ., 27:1185–1201)—designated in this paper as IMPROVE protocol. The use of a dual-optical instrument permitted simultaneous monitoring of the transmission (TOT [thermal-optical transmission]) and reflectance (TOR [thermal-optical reflectance]) for each protocol. Results show that the aerosols containing components susceptible to charring (such as water-soluble organic compounds typical of cookstove and rural aerosols) had higher OC/EC variability among the methods when compared with diesel-impacted aerosols (diesel and urban), which showed little to no “instrumentally calculated” pyrolyzed carbon (PyC). Thermal effects on the OC/EC ratios among the 3 TOT methods were significantly lower for diesel-impacted aerosols. Similar OC/EC findings were observed for the 3 TOR methods. Optical effects (TOT/TOR ratio) for the OC/EC ratio ranged from 1.37–1.71 (residential cookstoves), 1.63–2.23 (rural), 1.05–1.24 (diesel exhaust), and 0.80–1.12 (urban) for the 3 methods, with IMPROVE (TOT and TOR) always significantly lower when compared with NIST-EPA (TOT and TOR) and NIOSH (TOT and TOR) for all sample types. Thermal and optical effects on the EC/TC ratios were similar to those observed for the OC/EC ratios. Due to their distinct aerosol characteristics, different sample types behave differently under various thermal and optical conditions. Hence, use of a single TOA method to define OC/EC ratios for all aerosol types may not be feasible. Copyright 2012 American Association for Aerosol Research

Isolation and quantitative estimation of diesel exhaust and carbon black particles ingested by lung epithelial cells and alveolar macrophages in vitro

A new procedure for isolating and estimating ingested carbonaceous diesel exhaust particles (DEP) or carbon black (CB) particles by lung epithelial cells and macrophages is described. Cells were incubated with DEP or CB to examine cell-particle interaction and ingestion. After various incubation periods, the cells were separated from free extracellular DEP or CB particles by Ficoll density gradient centrifugation and dissolved in hot sodium dodecyl sulfate detergent. Insoluble DEP or CB residues were isolated by high-speed centrifugation, and the elemental carbon (EC) concentrations in the pellets were estimated by a thermal-optical-transmittance method (i.e., carbon analysis). From the EC concentration, the amount of ingested DEP or CB could be calculated. The described technique allowed the determination of the kinetics and dose dependence of DEP uptake by LA4 lung epithelial cells and MHS alveolar macrophages. Both cell types ingested DEP to a similar degree; however, the MHS macrophages took up significantly more CB than the epithelial cells. Cytochalasin D, an agent that blocks actin polymerization in the cells, inhibited approximately 80% of DEP uptake by both cell types, indicating that the process was actin-dependent in a manner similar to phagocytosis. This technique can be applied to examine the interactions between cells and particles containing EC and to study the modulation of particle uptake in diseased tissue.