2008 Progress Report: Effects of Global Change on the Atmospheric Mercury Burden and Mercury Sequestration Through Changes in Ecosystem Carbon PoolsEPA Grant Number: R833378
Title: Effects of Global Change on the Atmospheric Mercury Burden and Mercury Sequestration Through Changes in Ecosystem Carbon Pools
Investigators: Obrist, Daniel , Johnson, Dale W. , Lindberg, Steve , Luo, Yiqi
Institution: Desert Research Institute , University of Oklahoma , University of Nevada - Reno
Current Institution: Desert Research Institute , University of Nevada - Reno , University of Oklahoma
EPA Project Officer: Chung, Serena
Project Period: May 1, 2007 through April 30, 2012
Project Period Covered by this Report: May 1, 2008 through April 30,2009
Project Amount: $899,091
RFA: Consequences of Global Change For Air Quality (2006) RFA Text | Recipients Lists
Research Category: Global Climate Change , Climate Change , Air
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.
Year 3 of this project has had two research thrusts:
- Further development of electro-chemical sensors for monitoring atmospheric aerosol chemistry and field testing a system for online aerosol chemistry measurements with a suite of sensors. Work in this area was primarily undertaken at the University of Wisconsin.
- Investigating water-soluble Fe(II) in urban atmospheres based on extensive ambient measurements using the first instrument capable of near real-time (12 minute) measurements of speciated Fe. This instrument was developed in years 1 and 2 of the project. Work in this area was conducted mainly at Georgia Tech.
ISE Development: Efforts over the past year in this area were directed toward establishing new methods for several of the target analytes/species identified in the proposal, and more recently in field evaluation/validation of these methods.
Two approaches were investigated for quantifying trace levels of copper in ambient particles: (a) a spectrophotometric method using bathocuproine chemistry (BDH-Cu); and (b) a micro flow-through Ion Selective Electrode (ISE-Cu). Comparison between ICP-MS and the spectrophotometric method confirm the method (linear regression slope of 1.007, r2 = 0.98). A unique aspect of the BDH-Cu-LWCC method is the ability to distinguish Cu oxidation states, and we are currently conducting experiments using the selectivity of BDH for Cu(I) to determine ratios and absolute abundances of Cu(I) and Cu(II) in urban aerosol. The oxidation state information may be useful as a source tracer and the ratios as a redox probe and proxy for aerosol properties such as age or transport history/conditions/processing. ISE-Cu work was only begun during year 3 and results will be reported next year. (Note: A 1-year no-cost extension was granted for this project.) It is anticipated that these new online more highly time-resolved methods for speciating metals (e.g., Cu and Fe [see below]) will allow better studies aimed at understanding sources, atmospheric processing and the possible health impacts of these compounds.
In addition to the copper sensor work, two methods were investigated for nitrate detection: a UV-spectrophotometric method (UV-Nitrate) and a flow-through ionselective BioSensor (Bio-Nitrate). Both approaches are low cost, and relatively straightforward in concept and implementation. The analytical characteristics of a commercially available chloride microelectrode sensor were performed. At the end of the project's third year a suite of sensors that includes sodium, calcium (characterized in early work), nitrate, and chloride were integrated into a system for online aerosol speciation at a 1-hour time resolution. The goal is to develop a low-cost alternative to ion-chromatography for routine aerosol chemical analysis, as outlined in the project proposal.
Water-Soluble Fe(II) Results: A second thrust of the project has been to develop an instrument for online measurements of water-soluble Fe(II) (WS_Fe(II)) in ambient particles. This work directly addresses the project goal of developing online methods for measuring metals that could support future aerosol/health studies. Other research has found a link between metals in fine particles and adverse health outcomes. In the third year of this project the results describing an instrument developed in years 1 and 2 were summarized in a paper and published in the journal Environmental Science & Technology (Rastogi et al, 2009). Also, in the project's second (Detroit, MI) and third (Atlanta, GA) years, this instrument was deployed at a variety of sites to investigate sources of WS_Fe(II) and atmospheric processes that may influence concentrations. The key findings from this research were that although no clear diurnal trends in WS_Fe(II) were observed at any of the urban sites, high temporal variability was observed at all urban sites, where concentrations often changed from the LOD (5 ng m-3) to approximately 300 to 400 ng m-3 within a few hours, suggesting localized sources. In Detroit, Michigan, transient WS_Fe(II) events were observed when downwind of industrial sources located within 10 km to the south of the site. Emissions from this wind sector included a coal-fired power plant, cement kiln, large petroleum refinery, wastewater treatment plant, and two steel mills. The specific source could not be identified. In Atlanta elevated WS_Fe(II) concentrations were often correlated with sulfate, with highest concentrations associated with a more apparently acidic aerosol, suggesting that the low pH aerosol generated in coal-fired power-plant plumes leads to a more labile form of iron (i.e., WS_Fe(II)). At one Atlanta site, a WS_Fe(II) transient event that was not related to aerosol acidity was often observed in late evening , but the source was not identified. No correlation was ever observed between WS_Fe(II) and elemental carbon, indicating no direct relationship to mobile source emissions. Overall, measurements from the two urban sites indicate that WS_Fe(II) were possibly associated with direct industrial emissions or atmospheric processes that transform some fraction of the aerosol iron to WS_Fe(II). A manuscript describing these results was prepared in year 3 and submitted to the Journal of Geophysical Research. It is currently in review.
As noted above, a one-year no cost extension was granted for this project. Future activities to be undertaken during this 1-year extension are summarized below.
ISE Development: Work will continue on the development and characterization of the water-soluble Cu and the nitrate sensors. Both will be tested for use in ambient aerosol analysis using liquid filter extracts and online analysis using an Atmospheric Ion Monitor (AIM-URG Corp.) that collects particles into an aqueous slurry. The suite of ISEs integrated into the AIM will be field validated in the summer of 2009 by deployment in Madison, Wisconsin, and compared to integrated filter measurements of ions via traditional ion chromatography techniques. Results from the Cu analytical work will be presented at the fall 2009 AAAR conference (abstract has been submitted). Manuscripts have been outlined for the Cu-sensor and Nitrate-sensor studies and will be submitted in the fourth year of the project. The sodium and calcium data developed in the field experiment described above will be integrated into a previously drafted manuscript that details the potential of ISEs for near real-time characterization of atmospheric aerosol composition. This work addresses one of the major project goals.
Water-Soluble Fe(II): The manuscript discussed above, currently in review, will be completed in the fourth year. Work has also begun on expanding the WS_Fe(II) method to also allow speciation of WS_Fe(III). A prototype instrument has been developed and is currently deployed in Atlanta. If successful, a manuscript describing the method and findings from urban measurements will also be constructed in the fourth year. This work will address the project goal of developing online and near real-time methods for speciation of aerosol metals in support of aerosol-health studies.
Journal Articles on this Report : 1 Displayed | Download in RIS Format
|Other project views:||All 64 publications||21 publications in selected types||All 21 journal articles|
||Rastogi N, Oakes MM, Schauer JJ, Shafer MM, Majestic BJ, Weber RJ. New technique for online measurement of water-soluble Fe(II) in atmospheric aerosols. Environmental Science & Technology 2009;43(7):2425-2430.||