JOURNAL OF GEOPHYSICAL RESEARCH, VOL. 95, NO. D4, PAGES 3493–3507, 1990

Origins and variations of nitrate in south polar precipitation

Michel R. Legrand

Laboratoire de Glaciologie et Géophysique de l’Environnement, St-Martin-D’Hères, France

Séverine Kirchner

Laboratoire de Glaciologie et Géophysique de l’Environnement, St-Martin-D’Hères, France

Abstract

South polar firn cores spanning the last millennium have been analyzed to determine the nitrate background level of high-latitude precipitation and its temporal variations. The resulting data reveal no evidence of a positive correlation between solar activity (11-year solar cycle, low solar activity time periods, and solar proton events) and the NO₃ content of south polar snow. These data therefore suggest that NO_x production in the upper stratosphere, mesosphere, and thermosphere does not contribute significantly to the antarctic NO₃ budget. This study of the NO₃ content of high latitude precipitation suggests a major contribution by lightning (from a third to a half of the total) and by NO_x produced in the lower stratosphere (approximately a third from N₂O oxidation and to a lesser extent galactic cosmic rays) to the NO₃ budget of this background atmosphere, the remaining portion being related to the present NO_x surface sources of the southern hemisphere. For the first time, our data point to a decrease of NO₃ content when very large amounts of sulfuric acid are present in South Pole snow layers. This observation suggests a possible interaction (via the hydroxyl radical) between S- and N-derived species when large quantities of SO₂ are injected by volcanic eruptions. Although the deposition mechanism of HNO₃ in South Pole snow layers is far from well understood, our data suggest that only a minor amount of this compound is deposited directly on surface snow layers. Finally, the role played by particles (volcanic ash, terrestrial impurities, or ice particles) to enhance the uptake of odd nitrogen from the atmosphere by heterogeneous processes is discussed. In particular, it is suggested that in late winter, under certain meteorological conditions leading to ice particle formation, a significant uptake of NHO₃ from the lower stratosphere can occur. © American Geophysical Union 1990

Index Terms: 0340 Atmospheric Composition and Structure: Middle atmosphere—composition and chemistry; 3354 Meteorology and Atmospheric Dynamics: Precipitation.

Citation: Legrand, M. R., and S. Kirchner (1990), Origins and variations of nitrate in south polar precipitation, J. Geophys. Res., 95(D4), 3493–3507.

Copyright 1990 by the American Geophysical Union.