Hydrocarbon Measurements During the 1992 Southern Oxidants Study Atlanta Intensive: Protocol and Quality Assurance

Abstract

A major component of the Southern Oxidants Study (SOS) 1992 Atlanta Intensive was the measurement of atmospheric nonmethane hydrocarbons. Ambient air samples were collected and analyzed by a network of strategically located automated gas chromatography (GC) systems (field systems). In addition, an extensive canister sampling network was deployed. Combined, more than 3000 chromatograms were recorded. The SOS science team targeted for quantitative analysis 56 compounds which may be substantial contributors to ozone formation or used as air mass tracers. A quality assurance program was instituted to ensure that good measurements were being made throughout the network for each target compound. Common, high-quality standards were used throughout the network. The performance of individual field systems was evaluated during the intensive through the analysis of challenge mixtures. This methodology helped to identify and correct analytical problems as they arose.     

The OTC Challenge: Adding VOC Controls in the Northeast

The 1990 Clean Air Act Amendments create an ozone transport region made up of the northeastern and mid-Atlantic states. These new provisions call for VOC and NOx controls even in clean areas of the region in order to reduce ozone transport to downwind areas. The stationary and mobile source requirements will subject many air pollution sources to controls for the first time.

The provisions also create an Ozone Transport Commission, which can recommend that additional control measures be adopted in all or part of the region. So far, the commission has focused primarily on region-wide mobile source controls, such as California low emission vehicle standards and reformulated gasoline. But lately it has been paying increasing attention to stationary source measures, including NOx controls.     

Controlled Exposures of Volunteers to Respirable Carbon and Sulf uric Acid Aerosols

Respirable carbon or fly ash particles are suspected to increase the respiratory toxicity of coexisting acidic air pollutants, by concentrating acid on their surfaces and so delivering it efficiently to the lower respiratory tract. To investigate this issue, we exposed 15 healthy and 15 asthmatic volunteers in a controlled- environment chamber (21°C, 50 percent relative humidity) to four test atmospheres: (i) clean air; (ii) 0.5-μm H2SO4 aerosol at =100 μg/m³, generated from water solution; (iii) 0,5-μm carbon aerosol at =250 μg/m³, generated from highly pure carbon black with specific surface area comparable to ambient pollution particles; and (iv) carbon as in (iii) plus =100 μg/m³ of ultrafine H2SO4 aerosol generated from fuming sulfuric acid. Electron microscopy showed that nearly all acid in (iv) became attached to carbon particle surfaces, and that most particles remained in the sub-μm size range. Exposures were performed double-blind, 1 week apart. They lasted 1 hr each, with alternate 10-min periods of heavy exercise (ventilation =50 L/min) and rest. Subjects gargled citrus juice before exposure to suppress airway ammonia. Lung function and symptoms were measured pre-exposure, after initial exercise, and at endexposure. Bronchial reactivity to methacholine was measured after exposure. Statistical analyses tested for effects of H₂SO₄ or carbon, separate or interactive, on health measures. Group data showed no more than small equivocal effects of any exposure on any health measure. One individual's responses were consistent with a clinically significant excess airway constriction from H₂SO₄ plus carbon, and 2-3 others showed slight excess responses to the combined pollutants, but all these observations might have reflected chance variations. We conclude that coexisting carbon aerosol did not increase respiratory irritancy of H₂SO₄, in most healthy and asthmatic subjects exposed for 1 hr under simulated "worst-case" ambient conditions.     

Measurement of Volatile Organics at Part per Billion Concentrations Using a Cold Trap Inlet and High Speed Gas Chromatography

Direct inlet gas chromatography (GC) is becoming one of the most frequently used techniques for measurement of volatile organics in air. Although GC is an effective tool, its usefulness as a field method can be limited by retention times of several minutes or more, and by the limits of detection. In order to address these issues, a high speed GC system featuring a capillary cold trap inlet and variable speed electrometeramplifier was developed and tested.

The gas cooled inlet was used to collect and focus organic vapors from injection volumes of up to 1 ml. Resistance heating of the metal cold trap produced a narrow injection band that allowed simple separations to be completed in 5 to 20 seconds. Use of a variable speed electrometer-amplifier allowed the response time and noise suppression characteristics to be adjusted to the needs of the specific analysis.

Simple mixtures of organics including aromatics, alkanes and chlorinated hydrocarbons were separated in 20 seconds or less. The limits of detection for 13 test compounds ranged from less than 1 part per billion by volume (ppbv) to about 50 ppbv. Data presented here indicate that high speed GC using a cold trap inlet may be a feasible approach for near real-time measurement of volatile organics in ambient air.     

Assessment of Needs for Technical Information in EPA’s Hazardous and Solid Waste Programs

Headquarters managers and Regional staff in the U.S. Environmental Protection Agency’s hazardous and solid waste programs were surveyed to determine priorities for technical information and guidance among EPA Regional staff, state hazardous waste management staff, EPA contractors, and the regulated community. The survey also examined delivery systems effective for EPA Regional staff. The fifteen highest ranked technical needs for RCRA, Superfund, and UST reflect a pervasive interest in hazardous waste remediation. Top priority technical needs focus on establishing cleanup levels, subsurface fate and transport, field monitoring and quality assurance, remedy selection, and most importantly, which remedies work and which do not in specific situations. Technical needs of non- EPA audiences are quite similar to those for EPA field staff. Preferences for technology transfer delivery systems are generally for conventional distribution methods (such as print materials and workshops) rather than electronic or video media. Regional staff report serious problems in utilizing technology transfer because of time constraints, insufficient knowledge of available products, insufficient travel funds, and limited access to and training on computers.     

An Analysis of Biomedical Waste Incineration

The California Air Resources Board (ARB) completed a series of source tests of eight operating biomedical waste incinerators (BMWI) under conditions of typical operation. The emissions of certain metals, and chlorinated dioxins and furans in the flue gases of BMWI are relatively high in comparison to emissions from other combustion sources, such as hazardous waste or municipal waste incinerators of modern design. This study reports on an analysis of the status of the existing regulatory framework and the California data base. Clarification of definitional issues at the federal level is needed to effectively treat BMWI management issues. Although few relationships among combustion parameters and emissions were uncovered, patterns of emissions were evident, suggesting commonality and relationships among the waste stream constituents and emissions. Potential implications for future research, operation of BMWI, controls and source reduction and waste segregation strategies are also discussed.     

Seasonal Variations in Aerosol Composition and Acidity at Shenandoah and Great Smoky Mountains National Parks

The concentration of elements Na through Pb, select ions, and organic carbon from fine (<2.5 µm) particles has been monitored at Shenandoah and Great Smoky Mountains National Parks from 1988 through 1995. The data obtained from 1988 through 1994 show that significant changes in the concentrations of many aerosol constituents occur on a seasonal basis. Particulate sulfate and organic carbon are shown to exhibit substantially higher concentrations during the summer, while sulfur dioxide and nitrate concentrations are highest during the winter.

A method for estimating the degree of neutralization of particulate sulfate is given. This method uses routinely measured aerosol elemental compositions because ammonium ion, the primary neutralizing species for sulfate, is not measured on a routine basis. Application of this method to the selected data set shows that sulfate aerosol is most acidic during summer with an average molar H_s (moles of hydrogen associated with sulfur) to S (moles of sulfur) ratio of approximately 4. This suggests the average sulfate particle during the summer has a molar coon slightly more acidic than ammonium bisulfate (NH₄HSO₄) which has a molar hydrogen to sulfur ratio of 5. Winter H_s to S ratios, however, are approximately 8, suggesting the aerosol is on average fully neutralized ammonium sulfate [(NH₄)₂SO₄].     

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

ABSTRACT

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

Estimates of Particle Hygroscopicity during the Southeastern Aerosol and Visibility Study

ABSTRACT

Aerosol water content was determined from relative humidity controlled optical particle counter (ASASP-X) size distribution measurements made during the Southeastern Aerosol and Visibility Study (SEAVS) in the Great Smoky Mountains National Park during summer 1995. Since the scattering response function of the ASASP-X is sensitive to particle refractive index, a technique for calibrating the ASASP-X for any real refractive index was developed. A new iterative process was employed to calculate water mass concentration and wet refractive index as functions of relative humidity. Experimental water mass concentrations were compared to theoretically predicted values assuming only ammonium sulfate compounds were hygroscopic. These comparisons agreed within experimental uncertainty. Estimates of particle hygroscopicity using a rural aerosol model of refractive index as a function of relative humidity demonstrated no significant differences from those made with daily varying refractive index estimates. Although aerosol size parameters were affected by the assumed chemical composition, forming ratios of these parameters nearly canceled these effects.     

Analysis of a Summertime PM2.5 and Haze Episode in the Mid-Atlantic Region

Abstract

Observations of the mass and chemical composition of particles less than 2.5 μm in aerodynamic diameter (PM_2.5), light extinction, and meteorology in the urban Baltimore-Washington corridor during July 1999 and July 2000 are presented and analyzed to study summertime haze formation in the mid-Atlantic region. The mass fraction of ammoniated sulfate (SO₄ ^2-) and carbonaceous material in PM_2.5 were each ～50% for cleaner air (PM_2.5 < 10 μg/m³) but changed to ～60% and ～20%, respectively, for more polluted air (PM_2.5 > 30 μg/m³). This signifies the role of SO₄ ^2- in haze formation. Comparisons of data from this study with the Interagency Monitoring of Protected Visual Environments network suggest that SO₄ ^2? is more regional than carbonaceous material and originates in part from upwind source regions. The light extinction coefficient is well correlated to PM_2.5 mass plus water associated with inorganic salt, leading to a mass extinction efficiency of 7.6 ± 1.7 m²/g for hydrated aerosol. The most serious haze episode occurring between July 15 and 19, 1999, was characterized by westerly transport and recirculation slowing removal of pollutants. At the peak of this episode, 1-hr PM_2.5 concentration reached ～45 μg/m³, visual range dropped to ～5 km, and aerosol water likely contributed to ～40% of the light extinction coefficient.