2007 Progress Report: An Instrument for Real Time Speciation of Water Soluble Tracers in Atmospheric Particulate Matter

EPA Grant Number: R832835
Title: An Instrument for Real Time Speciation of Water Soluble Tracers in Atmospheric Particulate Matter
Investigators: Weber, Rodney J. , Schauer, James J. , Shafer, Martin M.
Institution: Duke University
Current Institution: Duke University , University of Wisconsin - Madison
EPA Project Officer: Hunt, Sherri
Project Period: May 1, 2006 through April 30, 2010
Project Period Covered by this Report: May 1, 2007 through April 30,2008
Project Amount: $492,354
RFA: Continuous Measurement Methods for Particulate Matter Composition (2005) RFA Text |  Recipients Lists
Research Category: Particulate Matter , Air , Air Quality and Air Toxics


The overall goal of this project is to configure, validate, and employ cost-effective real time instruments to measure water-soluble components of urban aerosols to support source apportionment efforts and human health studies.


The proposed instrument would measure the following species at a time resolution of one hour:

  1. Water soluble inorganic ions (Sulfate, Nitrate, and Ammonium)
  2. Water soluble crustal elements (Calcium, Potassium, and Sodium)
  3. Water soluble organic carbon (WSOC)
  4. Water soluble trace metals (Chromium (VI), Copper, Iron (II), and Manganese (II))

The collection and analytical methods that will be used for the proposed instruments directly build on methods that have been employed by the project team and will be integrated to yield an instrument that can be operated at air quality monitoring sites to measure:

  1. The hourly contribution of secondary inorganic aerosol to PM concentrations
  2. The hourly contribution of water-soluble organic carbon (WSOC) to particulate matter concentrations. WSOC is predominately associated with wood smoke and secondary organic aerosol (SOA) in urban environments.
  3. The hourly contribution of sodium from sea spray and road salt to PM concentrations.
  4. The hourly fingerprint of water soluble crustal elements associated with resuspended dust, wood burning, and industrial sources.
  5. The hourly concentrations of toxic metals that can be used as source tracers.

Progress Summary:

Progress Summary/Accomplishments: In the second year of the project work continued on acquiring and testing sensors, with a focus on ion-selective micro-electrodes (ISE). A potassium (K+) ISE was integrated with the Particle-Into-Liquid Sampler (PILS) for online measurements of aerosol composition. This instrument was calibrated in the laboratory and deployed in a prescribed burning fire in rural Georgia for two days of testing. Comparisons were made between a number of instruments and showed rapid measurement response to changes in ambient aerosol concentrations and agreement with integrated filter measurements of K+ (Regression parameters were: slope = 1.07, R2 = 0.75 for intercept forced through zero, and slope = 0.85, R2 = 0.86 for intercept = 0.52 μg m-3, N = 5). Work is underway on a manuscript describing our results applying ISE’s for ambient aerosol measurements.
A second thrust of this project has been to develop an instrument for online measurements of water-soluble iron (Fe2+) in ambient particles. In this instrument the PILS is used to concentrate ambient particles into a flow of purified water, which is then analyzed for Fe2+ by mixing with ferrozine to form a Fe-complex that uniquely absorbs at a wavelength of 562 nm. When combined with the PILS, measurement of absorption at 562nm relative to 700nm using a 1 m long Liquid Wave-guide Capillary Cell (LWCC) and spectrophotometer resulted in an ambient aerosol iron detection limit of 3.3 ng m-3. The relative standard deviation based on replicate measurements (n = 10) of 1 μg L-1 standard solution gave a precision of less than 3%. The overall uncertainty for the complete PILS-LWCC system was estimated at 12%. This instrument was deployed at a number of sites. Measurements were made in Atlanta in Nov. 2007 and April 2008. We also deployed the instrument as part of a LADCO-funded project in Detroit, MI, for the month of Jan. 2008. The temporal variability in Fe2+ was found to be in reasonable agreement a mass spectrometer measurement of total Fe. This work served as the Qualifying Exam project for Michelle Oakes, the Ph.D. student working on this project.

Expected Results:

The instrument developed under this project will enable measurements of these compounds to be readily obtained at state and local air quality monitoring sites. The data generated can be used along with STN data to identify sources of particulate matter and sources of toxic components of particulate matter. In addition, these measurements will provide a valuable data stream for health studies and air pollution model validation. This instrument will require limited operating and maintenance oversight and will be suitable for monitoring stations that are operated by a wide range of state and local agencies. The proposed project will develop and validate the instrument prototype and will demonstrate the operability and data analysis opportunities of the instrument during a year-long study.

Future Activities:

In the final year of the project we plan to finish and publish the paper on the PILS-ISE-K+ instrument. Most effort will focus on further developing the watersoluble iron system. We are working on two papers, one describing the method and the other reporting on our ambient studies. In the next year work will also focus on extending the measurement capabilities to include Fe3+. The goal is to have an instrument capable of online measurements of Fe2+ and Fe3+, at a 20-minute duty cycle. Field testing of the iron instrument in urban Atlanta will be continued into the third year and will involve comparisons with integrated filters and other methods for measuring iron.

Journal Articles:

No journal articles submitted with this report: View all 11 publications for this project

Supplemental Keywords:

carbonaceous aerosols, air toxics, emissions, polar compounds, water-soluble metals.
, RFA, Scientific Discipline, Air, particulate matter, air toxics, Environmental Chemistry, Environmental Monitoring, Atmospheric Sciences, ambient air quality, atmospheric particulate matter, inorganic aerosols, particulate organic carbon, real time measurement, airborne particulate matter, ambient measurement methods, Speciation Trends Sampler, air sampling, aerosol composition, airborne aerosols, PM, particulate matter components, particulate organic matter, trace metals, chemical speciation sampling

Progress and Final Reports:

Original Abstract
2006 Progress Report
2008 Progress Report
Final Report