Major influence of BrO on the NOx and nitrate budgets in the Arctic spring, inferred from Δ17O(NO3–) measurements during ozone depletion events
S. Morin A E , J. Savarino A , S. Bekki B , A. Cavender C , P. B. Shepson C and J. W. Bottenheim DA Laboratoire de Glaciologie et Géophysique de l’Environnement (LGGE), CNRS-UJF, Grenoble, France.
B Service d’Aéronomie du CNRS, IPSL, UPMC, Paris, France.
C Purdue University, West Lafayette, IN, USA.
D Meteorological Service of Canada, Toronto, ON, Canada.
E Corresponding author. Email: samuel.morin@lgge.obs.ujf-grenoble.fr
Environmental Chemistry 4(4) 238-241 https://doi.org/10.1071/EN07003
Submitted: 15 January 2007 Accepted: 7 May 2007 Published: 16 August 2007
Environmental context. Ozone depletion events (ODEs) in the Arctic lower atmosphere drive profound changes in the chemistry of nitrogen oxides (NOx) because of the presence of bromine oxide (BrO). These are investigated using the isotopic composition of atmospheric nitrate (NO3–), which is a ubiquitous species formed through the oxidation of nitrogen oxides. Since BrO is speculated to play a key role in the atmospheric chemistry of marine regions and in the free troposphere, our studies contribute to the improvement of the scientific knowledge on this new topic in atmospheric chemistry.
Abstract. The triple oxygen isotopic composition of atmospheric inorganic nitrate was measured in samples collected in the Arctic in springtime at Alert, Nunavut and Barrow, Alaska. The isotope anomaly of nitrate (Δ17O = δ17O – 0.52δ18O) was used to probe the influence of ozone (O3), bromine oxide (BrO), and peroxy radicals (RO2) in the oxidation of NO to NO2, and to identify the dominant pathway that leads to the production of atmospheric nitrate. Isotopic measurements confirm that the hydrolysis of bromine nitrate (BrONO2) is a major source of nitrate in the context of ozone depletion events (ODEs), when brominated compounds primarily originating from sea salt catalytically destroy boundary layer ozone. They also show a case when BrO is the main oxidant of NO into NO2.
Additional keywords: atmospheric chemistry, halogen compounds, isotopes, nitrates, ozone depletion events.
Acknowledgements
We thank the staff at the GAW laboratory in Alert who carried out the sampling at Alert. The Barrow Arctic Science Consortium and NSF are acknowledged for logistical support. We thank G. Patton and R. Schnell from NOAA, who lent us their spare HiVol pump at Barrow. J.-L. Jaffrezo and M. Baroni are acknowledged for laboratory support. The French Polar Institute (IPEV, grant OOTI 2005–no.440) and CEFIPRA/IFCPAR are acknowledged for their financial and scientific support. This work has been made possible thanks to the partial support from the European Science Foundation (ESF) under the EUROCORES Programme EuroCLIMATE, through contract No. ERAS-CT-2003-980409 of the European Commission, DG Research, FP6.
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1 δxO refers to the isotopic enrichment of a given oxygen isotope, calculated as Rxsample/Rxref – 1, where Rx is the isotope ratio xO/16O (x = 17 or 18) for the sample and an international reference material (Standard Mean Ocean Water for oxygen isotopes). δxO values are expressed in ‰.
