Signature of Arctic surface ozone depletion events in the isotope anomaly (Δ17O) of atmospheric nitrate S. Morin1, J. Savarino1, S. Bekki2, S. Gong3, and J. W. Bottenheim3 1Laboratoire de Glaciologie et de Géophysique de l'Environnement, Centre National de la Recherche Scientifique – Université Joseph Fourier, Grenoble, France 2Service d'Aéronomie, Institut Pierre Simon Laplace, Université Pierre-et-Marie Curie, Paris, France 3Environment Canada, Toronto, Ontario, Canada
Abstract. We report the first measurements of the oxygen isotope anomaly of atmospheric inorganic nitrate from the Arctic.
Nitrate samples and complementary data were collected at Alert, Nunavut, Canada (82°30 ' N, 62°19 ' W) in
spring 2004. Covering the polar sunrise period, characterized by the
occurrence of severe boundary layer ozone depletion events (ODEs), our data
show a significant correlation between the variations of atmospheric ozone
(O3) mixing ratios and Δ17O of nitrate
(Δ17O(NO−3)). This relationship can be expressed as:
Δ17O(NO−3)/‰, =(0.15±0.03)×O3/(nmol mol–1)+(29.7±0.7), with R2=0.70(n=12), for
Δ17O(NO−3) ranging between 29 and 35 ‰.
We derive mass-balance equations from chemical reactions operating in the Arctic boundary layer,
that describe the evolution of Δ17O(NO−3) as a function of the concentrations of reactive species and their isotopic characteristics.
Changes in the relative importance of O3, RO2 and BrO
in the oxidation of NO during ODEs, and the large isotope anomalies
of O3 and BrO, are the driving force for the
variability in the measured Δ17O(NO−3) . BrONO2
hydrolysis is found to be a dominant source of nitrate in the Arctic boundary
layer, in agreement with recent modeling studies.
Citation: Morin, S., Savarino, J., Bekki, S., Gong, S., and Bottenheim, J. W.: Signature of Arctic surface ozone depletion events in the isotope anomaly (Δ17O) of atmospheric nitrate, Atmos. Chem. Phys., 7, 1451-1469, doi:10.5194/acp-7-1451-2007, 2007.