Final Report: Development of a Semi-Continuous Monitor for Determination of Trace Elements and Heavy Metals in Ambient Aerosol Particles

EPA Grant Number: R825269
Title: Development of a Semi-Continuous Monitor for Determination of Trace Elements and Heavy Metals in Ambient Aerosol Particles
Investigators: Ondov, John M. , Koutrakis, Petros , O'Haver, T. C.
Institution: University of Maryland
EPA Project Officer: Shapiro, Paul
Project Period: November 15, 1996 through November 14, 1999 (Extended to November 14, 2000)
Project Amount: $395,885
RFA: Air Quality (1996) RFA Text |  Recipients Lists
Research Category: Air Quality and Air Toxics , Air

Objective:

The objectives of the project were to: (1) develop a semicontinuous system for determining the concentration of important elemental constituents of aerosol particles in ambient air with aerodynamic diameters <2.5 µm; and (2) deploy the system in College Park, MD, a nonindustrial area whose few generic sources are well described by existing chemical mass balance models.

Summary/Accomplishments (Outputs/Outcomes):

A system capable of collecting sufficient quantities of PM2.5 mass for multielement analysis by atomic absorption spectrometry has been developed. The system employs particle growth by condensation of water vapor, followed by aerosol concentration in a virtual impactor and subsequent collection of the resulting aerosol droplets in an impinger by real impaction. The system is comprised of an all-glass coaxial steam injector, and specially-designed water-trap condenser, and provides PM in an aqueous slurry for elemental analysis.

To reduce trace metal contamination, an all-glass steam injector, condenser, and twin-nozzle virtual impactor (VI) were constructed and tested at UMCP. At a minor-to-major flow rate ratio of 0.15, the VI provides a 0.7 µm cutpoint at 200 LPM. The efficiency of the final glass concentrator with steam injectors and condensers in place is 70 percent for submicrometer particles and 100 percent for supermicrometer particles. The efficiency of condensational growth is about 75 percent for hydrophobic submicrometer particles (Polystyrene Latex test particles) and is substantially greater that this for hygroscopic particles. In Baltimore, where hydrophobic particles comprise about 20 percent of the submicrometer aerosol mass, the overall submicrometer collection efficiency for the system would be about 95 percent. The SEAS has been operated successfully for a test period of 3 weeks without downtime to software problems.

A preliminary field test of the sampling system, fitted with the prototype glass virtual impactor, in College Park, MD, in November 1999. The sampler was mounted in a laboratory at UMCP with the outdoor inlet located 2-m above ground level near a campus parking lot. Samples were collected at 170 L?min-1 in 30 minute intervals from 4 a.m. - 9 p.m. for 3 days. Blanks were collected during the first and last hours of operation by placing an absolute fluted filter capsule on the sampler inlet. Elemental analysis by GFAAS showed sample-to-blank ratios of 3 - 30 for As, Al, Cd, Cu, Fe, Mn, Se, and Zn, and 1 - 3 for Cr and Ni. Preliminary results show excellent time resolution which allows for far better identification of transient source influences than achieved by current sampling/analytical strategies.

Figure 1 shows that the influence of motor vehicle emissions and suspended urban dust (Fe) closely follow local traffic patterns. The morning rush hour is clearly evident beginning at 7:30 a.m. as concentrations rise four-fold above background levels. The evening rush hour was particularly heavy due to a basketball game on campus, and again this is visible beginning at 5:00 p.m. Time series plots for other elements show the influence of a coal-fired power plant (Se) and a municipal incinerator (Pb) located 25-km southwest. Winds during this period shifted from northeast to the southwest by 11:30 a.m. facilitating exposure to the power plant plume between 12:30 p.m. and 4:30 p.m. with Se concentrations10-fold above background. The incinerator plume is also visible in two peaks, i.e., at 2:00 p.m. and 7:00 p.m., with Pb concentrations four-fold above background. Results of standard Principle Components Analysis show excellent resolution of the various marker elements in accordance with the time series plots. In addition, application of PFA (Kidwell, et al., 2000b), and advanced factor analysis method which allows weighting of individual datum, successfully associated identifiable source factors with appropriate wind directions. To our knowledge, this is the first accurate multielement aerosol particle data series achieved with 30 minute resolution.

Figure 1. Fe concentrations on November 18, 1999


Journal Articles on this Report : 3 Displayed | Download in RIS Format

Other project views: All 4 publications 4 publications in selected types All 4 journal articles
Type Citation Project Document Sources
Journal Article Kidwell CB, Ondov JM, Sioutas C, Koutrakis P. Ambient aerosol concentration by condensation and virtual impaction for collection and chemical analysis. Journal of Aerosol Science 1998;29(S2):S1039-S1040. R825269 (1999)
R825269 (Final)
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  • Journal Article Kidwell CB, Ondov JM. Development and evaluation of a prototype system for collecting sub-hourly ambient aerosol for chemical analysis. Aerosol Science and Technology 2002;35(1):596-601. R825269 (1999)
    R825269 (Final)
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  • Journal Article Kidwell CB, Ondov JM. Elemental analysis of sub-hourly ambient aerosol collections. Aerosol Science and Technology 2004;38(3):205-218. R825269 (Final)
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  • Supplemental Keywords:

    ambient air, particles, metals, heavy metals, environmental chemistry, measurement methods, analytical methods, Chesapeake Bay, MidAtlantic States, Maryland, MD, EPA Region 3., RFA, Scientific Discipline, Air, Geographic Area, particulate matter, air toxics, Environmental Chemistry, State, tropospheric ozone, Atmospheric Sciences, environmental monitoring, monitoring, calibration procedures, spectroscopic studies, ecological assessment, Maryland (MD), atmospheric chemical cycles, atmospheric aerosol particles, atmospheric monitoring, aerosol sampling, atomic absorption technology, aerosol production, aerosols, metals

    Relevant Websites:

    http://www.chem.umc.edu/supersite

    Progress and Final Reports:

    Original Abstract
  • 1997
  • 1998
  • 1999 Progress Report