1999 Progress 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 - College Park
Current Institution: University of Maryland
EPA Project Officer: Shapiro, Paul
Project Period: November 15, 1996 through November 14, 1999 (Extended to November 14, 2000)
Project Period Covered by this Report: November 15, 1998 through November 14, 1999
Project Amount: $395,885
RFA: Air Quality (1996) RFA Text |  Recipients Lists
Research Category: Air Quality and Air Toxics , Air


The objectives of the project are 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.

Progress Summary:

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 a real impactor. 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, a prototype glass twin-nozzle virtual impactor was constructed and tested at UMCP. Its collection efficiency, as a stand-alone unit, was found to be 60 percent for dry 2 µm particles and 80 percent for particles 3 µm and larger, and the D50 was 1.8 µm. Because of the higher pressure drop associated with a two-nozzle design, the maximum flow rate was only 170 L?min-1. The collection efficiency of the entire system (i.e., inlet tubing, flow splitter, steam injectors, glass condensers, glass virtual impactor, real impactor, and collection vials) was determined to be 45 percent for particles < 1 µm in diameter and gradually increased with size to about 70 percent efficiency for 3 µm particles. Additional tests with metal components suggest that improvements in the condenser water trap and achieving better nozzle alignment in subsequent construction should bring the overall system efficiency to 65 percent and 90 percent for fine and coarse particles, respectively.

A preliminary field test of the sampling system, fitted with the prototype glass virtual impactor, was conducted 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 4:00 a.m.?9:00 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 graphite furnace atomic absorption spectrometry (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 the influence of motor vehicle emissions on suspended urban dust (Fe), which closely follows local traffic patterns. The morning rush hour clearly is evident beginning at 7:30 a.m. as concentrations rise 4-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 concentrations 10-fold above background. The incinerator plume also is visible in two peaks (i.e., at 2:00 p.m. and 7:00 p.m., with Pb concentrations 4-fold above background. Preliminary results of factor analysis show excellent resolution of the various marker elements in accordance with the time series plots. 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

Future Activities:

Analysis of results collected in College Park, MD, will continue through the near future. Factor analysis will be performed on the samples to determine the influence of local sources. These results then will be compared to chemical mass balance model results. An improved all-glass impactor and improved condenser will be built, and the system will be field tested in Baltimore later this year.

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 Ding YM, Ferguson ST, Wolfson JM, Koutrakis P. Development of a high volume slit nozzle virtual impactor to concentrate coarse particles. Aerosol Science and Technology 2001;34(3):274-283. R825269 (1999)
  • Abstract: InformaWorld Abstract
  • 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)
  • Abstract: Science Direct Abstract
  • 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)
  • Abstract: InformaWorld Abstract
  • Supplemental Keywords:

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

    Progress and Final Reports:

    Original Abstract
  • 1997
  • 1998
  • Final Report