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Grantee Research Project Results

Evaluating Sources of Chemical Pathways of Aerosol Production on the Southern Ute Indian Reservation and Navajo Nation Using Isotopic and Geochemical Analysis

EPA Grant Number: FP917291
Title: Evaluating Sources of Chemical Pathways of Aerosol Production on the Southern Ute Indian Reservation and Navajo Nation Using Isotopic and Geochemical Analysis
Investigators: King, Michael Zane
Institution: Purdue University - Main Campus
EPA Project Officer: Zambrana, Jose
Project Period: August 1, 2011 through July 31, 2013
Project Amount: $84,000
RFA: STAR Graduate Fellowships (2011)
Research Category: Academic Fellowships , Fellowship - Tribes and American Indian/Alaska Native/Pacific Islander Communities



Increased emissions of nitrogen oxides (NOx) as a result of the development of oil, gas and coal resources in the Four Corners region of the United States have caused concern for area American Indian tribes that levels of ozone, acid rain and aerosols or particulate matter (PM) may increase on reservation lands. NOx in the atmosphere plays an important role in the formation of these pollutants and high levels are indicators of poor air quality, and exposure to them has been linked to a host of human health effects and environmental problems facing today’s society. Nitrogen oxides are eventually oxidized in the atmosphere to form particulate nitrate and nitric acid, which falls to earth’s surface by way of dry or wet deposition. In the end, it is the removal of NOx from the atmosphere by chemical conversion to nitrate that halts this production of oxidants, acid and aerosols. Despite the importance of understanding atmospheric nitrate production, there remains major deficiencies in estimating the significant key reactions that transform atmospheric NOx. This project will examine the stable isotope composition of particulate nitrate (PM2.5-PM10) collected on the Southern Ute Indian Reservation and Navajo Nation to provide insight into the sources of NOx and the oxidation pathways that convert NOx into nitrate on these reservation lands.


The first part of the research will be to request archival PM2.5 and PM10 filters for the years 2007 and 2009 to be released from the Southern Ute Indian Tribe (SUIT) and Navajo Nation to the Department of Earth and Atmospheric Sciences at Purdue University. Both the SUIT and Navajo Nation operate PM monitoring networks as part of the U.S. EPA PM national monitoring network. Nitrate (NO3) from the filters will be extracted, purified and concentrated using preparative ion chromatography (IC). In addition, trace metals such as lead, copper, nickel and zinc and major cations such as calcium, magnesium and sodium will be measured by Inductively Coupled Plasma Optical Emission Spectrometry (ICP-OES). The total isotopic composition of the nitrate will be carried out using the denitrifier technique, in which the nitrate is added to a solution containing a unique strain of denitrifying bacteria that convert NO3 into gaseous nitrous oxide (N2O). The N2O is collected using a headspace extraction device and gas chromatograph before being passed over a gold reaction tube where the N2O is quantitatively converted into nitrogen (N2) and oxygen (O2). Isotopic analysis on the product N2 and O2 will be done using a continuous flow isotope ratio mass spectrometer (IRMS) to determine the δ15N, δ18O, and cap δ17O values. Lastly, the Regional Atmospheric Chemistry Mechanism (RACM) photochemical box model will be used to predict nitrate cap δ17O values, which would then be compared to the observed data obtained from the PM filters. The RACM model will be initialized using air quality data obtained from the SUIT and Navajo Nation air quality programs. All isotopic measurements of nitrate extracted from tribal PM filters will be carried out at the Purdue Stable Isotopes Laboratory under the direction of Professor Greg Michalski. All data collected from tribal PM filters will be shared with tribal air quality programs, and biannual research updates will be presented to tribal air quality staff and Tribal Council members.

Expected Results:

The 1990 Clean Air Act (CAA) amendments authorized the EPA to allow Indian tribes to implement CAA programs in Indian Country under the Tribal Authority Rule (TAR). However, most tribes lack the resources needed to develop comprehensive air programs. Of the four tribes in the Four Corners region, the Navajo Nation and SUIT have established air quality programs under the TAR and have “Treatment as State” status, which allows tribes to monitor ambient air as well as develop federally enforceable air quality regulations to reduce air pollution on reservation lands. The data and results from this project will provide tribes with additional insight into the atmospheric processes that control air quality over tribal lands. This project will provide the SUIT and Navajo Nation insight into the sources of NOx and chemical pathways that convert NOx into nitrate over tribal lands. Isotopic analysis of nitrate will provide a baseline assessment to assist tribal air quality programs with their continual development of policies and regional planning efforts to improve air quality and protect the health and welfare of tribal members and residents.

Potential to Further Environmental/ Human Health Protection

The delegation of authority from the EPA to the Navajo Nation and forthcoming SUIT to implement operating permitting programs and regulations to reduce air pollution on reservation lands are the first of its kind in Indian Country. With ambient air quality measurements in the Four Corners region indicating ozone levels approaching “non-attainment” with existing National Ambient Air Quality Standards (NAAQS), it is extremely important that tribal air quality programs continue to actively participate with air quality regulatory agencies to cooperatively reduce regional air pollution. Both the Navajo Nation and Southern Ute Indian Reservation are home to numerous minor sources and several major sources of air pollution in the Four Corners region. This project may help in assessing how expected NOx emissions from power plants and increases in oil and gas exploration on these reservation lands might impact local tribal air quality, specifically ozone and particulate concentrations. The results can then supplement tribal air quality permitting programs and assist tribes with their continual development of policies and regional planning efforts to improve air quality and protect human health and the health of future generations to come.

Supplemental Keywords:

particulate matter (PM), PM2.5, PM10, nitrogen oxides, ozone, Tribal Authority Rule, NAAQS, nitrate, stable isotopes, Clean Air Act

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The perspectives, information and conclusions conveyed in research project abstracts, progress reports, final reports, journal abstracts and journal publications convey the viewpoints of the principal investigator and may not represent the views and policies of ORD and EPA. Conclusions drawn by the principal investigators have not been reviewed by the Agency.

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