George A. Klouda

Sources of Urban Contemporary Carbon Aerosol

Emissions from the major sources of fine carbonaceous aerosol in the Los Angeles basin atmosphere have been analyzed to determine the amounts of the ^(12)C and ^(14)C isotopes present. From these measurements, an inventory of the fossil carbon and contemporary carbon particle emissions to the Los Angeles atmosphere has been created. In the winter, more than half of the fine primary carbonaceous aerosol emissions are from sources containing contemporary carbon, including fireplaces, charbroilers, paved road dust, cigarette smoke, and brake lining dust, while in the summer at least one-third of the carbonaceous particle emissions are contemporary. Using a mathematical model for atmospheric transport, predictions are made of the atmospheric fine particulate fossil carbon and contemporary carbon concentrations expected due to primary source emissions. Model predictions are in reasonable agreement with the measured radiocarbon content of the fine ambient aerosol samples. It is concluded that the high fraction of contemporary carbon measured historically in Los Angeles is not due to local emission sources of biogenic material; rather, it is due to a combination of local anthropogenic pollution sources and background marine aerosol advected into the city.

Distinguishing the Contributions of Residential Wood Combustion and Mobile Source Emissions Using Relative Concentrations of Dimethylphenanthrene Isomers

As part of the United States Environmental Protection Agencys Integrated Air Cancer Project, air particulate matter samples collected in Boise, ID, were analyzed by gas chromatography with mass spectrometric detection (GC-MS) and apportioned between their two main sources : residential wood combustion (RWC) and motor vehicle (MV) emissions. The technique used for distinguishing the source contributions involved comparison of the concentration of 1,7-dimethylphenanthrene (1,7-DMP), a polycyclic aromatic hydrocarbon (PAH) emitted primarily by burning soft woods (e.g., pines), with that of a PAH emitted in modest concentrations by both RWC and MV sources, 2,6-dimethylphenanthrene (2,6-DMP). These results were then compared with the mean 1,7-DMP/2,6-DMP ratio of 48 samples collected in a roadway tunnel, with any enrichment in the Boise sample ratios over the mean tunnel ratio attributable to the RWC source. These resulting RWC contributions were compared with fraction RWC results obtained by radiocarbon measurements ( 14 C/ 13 C) of the same extracts from Boise, with generally good correlations between the two techniques observed, suggesting that the methods are comparable when used to distinguish emissions of MVs from RWC of soft woods.

Analysis of insoluble carbonaceous materials from airborne particles collected in pristine regions of colorado

Abstract Atmospheric particulate samples collected from remote mountainous locations in Colorado were extracted in sequence with methanol, methylene chloride, acetone and hexane. The resulting insoluble material was investigated using pyrolysis-mass spectrometry (Py-MS) and accelerator mass spectrometric 14 C analysis. The pyrolysis produced a complex mixture of aromatic and aliphatic hydrocarbons. The aliphatic hydrocarbons were postulated as being derived from vegetation. The 14 C analysis and the GC/MS results suggested that the aromatics occurred from combustion of living materials and also from long-range transport of industrial pollution. Appropriate samples from power plants and controlled forest fires were used to substantiate the conclusions.

Assessment of contemporary carbon combustion source contributions to urban air particulate levels using carbon-14 measurements.

w Measurement of carbon-14 activities with new low-level counting methods has been demonstrated to be an effective tool for assessing the contribution of contemporary carbon combustion sources to the mass collected with typical highvolume air samplers. This study represents the first time that radiocarbon measurements have been applied to fine particles (<2 pm) and used to assess the contribution of specific sources to urban air quality. Radiocarbon analysis of fine particles minimized interferences from large particles such as pollen, spores, wood fiber, etc., and improved the method’s ability to assess the impact of burning vegetative material such as field and slash burning and space heating with wood. Slash burning contributed between 39% and 70% of the fine particulate mass while field burning contributed 50% of the total suspended particulates (TSPs) on high-impact days in the Portland and Eugene, OR, airsheds. Radiocarbon analysis of filters selected for high impact from residential wood combustion shows that this source is a substantial contributor to fine particulate mass during winter months in Portland, OR.

The stable carbon isotope composition of atmospheric PAHs

Abstract A method for compound-specific stable carbon isotope analysis of atmospheric polycyclic aromatic hydrocarbons (PAHs) in carbonaceous aerosols is described. Atmospheric aerosol samples containing PAHs (C-10 to C-20) were collected on filters using a high-volume sampling technique, solvent extracted, taken through a cleanup procedure, separated by gas chromatography, oxidized to CO 2 on-line, and introduced into an isotope ratio mass spectrometer for analysis. The method can be used to determine the isotope composition of a few nanograms of PAHs. This technique was used to analyse and compare the isotope composition of atmospheric PAHs from standards, as well as two samples from urban and rural locations. Isotopic variability in atmospheric PAHs is greater than measurement uncertainties which makes this a potentially useful technique for source identification when used together with concentration measurements.

A method to determine collection efficiency of particles by swipe sampling

A methodology was developed to evaluate particle collection efficiencies from swipe sampling of trace residues. Swipe sampling is used for many applications where trace residues must be collected, including the evaluation of radioactive particle contamination and the analysis of explosives and contraband at screening checkpoints using ion mobility spectrometry (IMS). Collection efficiencies were evaluated for micrometer-sized polystyrene latex (PSL) spheres with respect to the particle size and mode of deposition, collection trap, surface type and swiping force. Test surfaces containing particles were prepared under controlled conditions and swiped with a reproducible technique that allows for the evaluation of frictional forces. Collection efficiencies were determined by optical imaging and particle counting. Of the two IMS collection traps studied, the polytetrafluoroethylene (PTFE) trap has significantly lower collection efficiencies. This is likely to be due to a combination of texture and composition. The larger (42 µm diameter) particles are collected more efficiently than the smaller (9 µm diameter) particles. Particles in a matrix similar to latent fingerprints are collected more efficiently than dry particles. Applying greater force during swiping does not greatly improve collection efficiencies. This fact, coupled with the observation that many particles are detached but not collected, implies that improvements in collection efficiency are dependent on improvements in adhesion of the particles to the collection surface, rather than larger forces to detach the particles.

Reference Material 8785: Air Particulate Matter on Filter Media

Reference Material (RM) 8785 Air Particulate Matter on Filter Media is intended primarily for use in the evaluation of analytical methods used to characterize the carbon composition of atmospheric fine particulate matter (PM) for national air quality monitoring programs. This RM consists of a fine fraction (nominally < 2.5 μ m aerodynamic diameter) of standard reference material (SRM) 1649a Urban Dust resuspended in air and filtered onto quartz-fiber filters. RM 8785 will also provide the atmospheric-chemistry and ocean-sciences communities with a means to intercompare methods and laboratories for the measurement of elemental (black) carbon. RM 8785 has values assigned for total carbon, elemental carbon, and organic carbon mass fractions measured according to two thermal–optical methods: the Interagency Monitoring of Protected Visual Environments (IMPROVE) and Speciation Trends Network–National Institute of Occupational Safety and Health (STN–NIOSH) protocols. Each filter is uniquely identified by its air particulate matter (APM) number and its gravimetrically determined mass of fine SRM 1649a. We will discuss the method used to produce RM 8785 and the results of an intermethod and interlaboratory comparison that provided assigned values for the above analytes.

Atmospheric carbon: The importance of accelerator mass spectrometry

Abstract Knowledge of the sources, transport and sinks for carbonaceous gases and particles in the atmosphere is of great concern both for understanding the carbon cycle and for assessing mans influence on atmospheric visibility, health effects and climate. Carbon isotopes (notably 14C) are quite important in tracing such species and in validating models based on emissions inventories, dispersion algorithms, and trace inorganic or organic mass balance. Accelerator mass spectrometry (AMS) offers considerable promise to this field, for useful sample size may be decreased by three orders of magnitude, resulting in greatly improved spatial, temporal and chemical resolution. Special problems which have been addressed with the use of 14C-AMS are reviewed, including the study of sources of elemental, organic (paniculate), and gaseous carbon compounds in the atmosphere. This report concludes with a brief review of techniques which have been used for 10–100 μg carbon samples, and a discussion of special atmospheric (urban particulate) Standard Reference Materials.

Fossil- and bio-mass combustion: C-14 for source identification, chemical tracer development, and model validation

Abstract Carbonaceous gases and aerosols emitted during fossil- and bio-mass combustion processes have significant impacts on regional health and visibility, and on global climate. 14 C accelerator mass spectrometry (AMS) has become the accepted standard for quantitatively partitioning individual combustion products between fossil and biospheric sources. Increased demands for source apportionment of toxic gases/vapors such as carbon monoxide and benzene, and toxic aerosol species such as polycyclic aromatic hydrocarbons, however, have led to increased needs for chemical source tracers. As a result, the application of atmospheric 14 C measurements has been extended to the discovery of new chemical tracers and the validation of the related apportionment models. These newer applications of 14 C are illustrated by recent investigations of: 1) sources of excessive concentrations of carbon monoxide and benzene in the urban atmosphere during the winter, as related to combustion source control strategies; and 2) the development/validation of potassium and hydrocarbon tracer models for the apportionment of mutagenic aerosols from biomass (wood) burning and motor vehicle emissions. Among the important consequences of these studies are new insights into potential limitations of elemental tracer models for biomass burning, and the impact of bivariate (isotopic, mass) chemical blanks on atmospheric 14 C-AMS data.

preparation of microgram samples on iron wool for radiocarbon analysis via accelerator mass spectrometry: A closed-system approach☆

Abstract A technique has been developed at NBS for the production of high quality targets for radiocarbon analysis by accelerator mass spectrometry (AMS). Our process optimizes chemical yields, ion currents and characterizes the chemical blank. The approach encompasses sample combustion to CO2, catalytic reduction of CO2 by Zn to CO, reduction to graphitic carbon on high-purity iron wool and in situ formation of a homogeneous iron-carbon bead; all steps are performed in a closed system. The total measurement system blank and variability are considered in the light of contributions from combustion, iron wool, reduction, bead formation and instrument blank. Additionally, use of this approach provides an increase in throughput, i.e. the effective management of large numbers of samples. Chemical yields for 50–800 μg C samples deposited on 15 mg iron wool were greater than 90%. Integrated 12C− ion currents observed were significant, being 4–64% of those observed in pure graphite. These currents are about an order of magnitude greater than those expected from dilution of graphite with an inert substrate. Isotopic accuracy, precision and blank were assessed by measuring the 14 C 13 C ratios of a series of targets prepared from dead carbon and oxalic acid (SRM 4990C). Each target was typically measured for one hour; bead consumption was estimated at 5% to 10%. System blank subsequent to combustion was equivalent to (2.2 ± 0.5) μg modern carbon (chemistry + instrument); combustion blank currently stands at (0.4 ± 0.1) (SE, n = 6) μg C.