Web Release Date: October 20,
Nitrogen Isotopes as Indicators of NOx Source Contributions to Atmospheric Nitrate Deposition Across the Midwestern and Northeastern United States
and
U.S. Geological Survey, Water Resources Division, 345 Middlefield Road, Menlo Park, California 94025, University of Pittsburgh, Department of Geology and Planetary Science, 4107 O'Hara Street, Pittsburgh, Pennsylvania 15260-3332, U.S. Geological Survey, New York Water Science Center, 425 Jordan Road, Troy, New York 12180, Department of Environmental Science, Policy & Management, 137 Mulford Hall, University of California, Berkeley, California 94720, National Atmospheric Deposition Program Central Analytical Lab, Illinois State Water Survey, 2204 Griffith Drive, Champaign, Illinois 61820-7495, Institute of Ecosystem Studies, Box AB, Millbrook, New York 12545-0129, and Department of Ecology and Evolutionary Biology, Cornell University, Ithaca, New York 12545-0129
Received for review April 16, 2007
Revised manuscript received August 9, 2007
Accepted August 22, 2007
Abstract:
Global inputs of NOx are dominated by fossil fuel
combustion from both stationary and vehicular sources
and far exceed natural NOx sources. However, elucidating
NOx sources to any given location remains a difficult
challenge, despite the need for this information to develop
sound regulatory and mitigation strategies. We present
results from a regional-scale study of nitrogen isotopes
(
15N) in wet nitrate deposition across 33 sites in the
midwestern and northeastern U.S. We demonstrate that
spatial variations in 15N are strongly correlated with NOx
emissions from surrounding stationary sources and
additionally that 15N is more strongly correlated with
surrounding stationary source NOx emissions than pH, SO42-,
or NO3- concentrations. Although emission inventories
indicate that vehicle emissions are the dominant NOx source
in the eastern U.S., our results suggest that wet NO3-
deposition at sites in this study is strongly associated with
NOx emissions from stationary sources. This suggests
that large areas of the landscape potentially receive
atmospheric NOy deposition inputs in excess of what one
would infer from existing monitoring data alone. Moreover,
we determined that spatial patterns in 15N values are a
robust indicator of stationary NOx contributions to wet NO3-
deposition and hence a valuable complement to existing
tools for assessing relationships between NO3- deposition,
regional emission inventories, and for evaluating progress
toward NOx reduction goals.
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