HR: 14:35h
AN: A43F-04    [Abstracts]
TI: Isotopes of HNO₃ in Air and Snow at Summit, Greenland
AU: * Jarvis, J C
EM: jjarvis@u.washington.edu
AF: Department of Earth and Space Sciences, University of Washington, Box 351310, Seattle, WA 98195, United States
AU: Hastings, M G
EM: mhasting@atmos.washington.edu
AF: Joint Institute for the Study of the Atmosphere and Ocean and Department of Atmospheric Sciences, Box 351640, Seattle, WA 98195, United States
AU: Steig, E J
EM: steig@u.washington.edu
AF: Department of Earth and Space Sciences, University of Washington, Box 351310, Seattle, WA 98195, United States
AB: The ice core record of nitric acid (HNO₃, or nitrate, NO₃^-), a final sink for atmospheric NO and NO₂, potentially contains valuable information about past changes in our atmosphere. Through reactions with OH and ozone, NO_x (NO and NO₂) is closely linked to the oxidizing capacity of the atmosphere. However, the interpretation of nitrate ice core records is complicated by post-depositional processing of nitrate, whereby photolysis and volatilization can result in nitrate losses from the snow surface. Quantitatively understanding the air-to-snow transfer of nitric acid is a necessary step in unraveling ice core records of nitrate. We present isotopic measurements (¹⁵N/¹⁴N and ¹⁸O/¹⁶O) of HNO₃ in air and snow from Summit, Greenland. Preliminary results show that the δ¹⁵N of HNO₃ is similar in surface snow and in air sampled 1.5 meters above the snow surface. The δ¹⁸O of HNO₃ is significantly higher in the surface snow versus the air samples. Previous studies of nitrate in precipitation have suggested that the δ¹⁵N of nitrate is influenced by sources of precursor NO_x while the δ¹⁸O of nitrate is influenced by the chemical pathways of nitrate production. We discuss the possibility that the difference in δ¹⁸O between the air and snow samples may be an indication that the air samples contain nitrate that was photolyzed and recycled from the snow surface. The similarity between δ¹⁵N in air and snow samples suggests that, despite the possibility of nitrate recycling, there is no net loss of nitrate from the snow surface. The utility of comparisons between variations in the δ¹⁵N of nitrate and changes in the source regions of air masses reaching Summit will also be discussed.
DE: 0365 Troposphere: composition and chemistry
DE: 0454 Isotopic composition and chemistry (1041, 4870)
DE: 0793 Biogeochemistry (0412, 0414, 1615, 4805, 4912)
DE: 1041 Stable isotope geochemistry (0454, 4870)
SC: Atmospheric Sciences [A]
MN: 2007 Fall Meeting