Signature of Arctic surface ozone depletion events in the isotope anomaly (Δ 17 O) of atmospheric nitrate

• Main Authors: S. Morin, J. Savarino, S. Bekki, S. Gong, J. W. Bottenheim
• Format: Article in Journal/Newspaper
• Language: English
• Published: Copernicus Publications 2007
• Subjects: Physics; QC1-999; Chemistry; QD1-999; Arctic; Nunavut; Canada
• Online Access: https://doaj.org/article/8c0e307e1d184e26a85de361cfd3a0d7

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 (O 3 ) mixing ratios and Δ 17 O of nitrate (Δ 17 O(NO − 3 )). This relationship can be expressed as: Δ 17 O(NO − 3 )/‰, =(0.15±0.03)×O 3 /(nmol mol –1 )+(29.7±0.7), with R 2 =0.70(n=12), for Δ 17 O(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 Δ 17 O(NO − 3 ) as a function of the concentrations of reactive species and their isotopic characteristics. Changes in the relative importance of O 3 , RO 2 and BrO in the oxidation of NO during ODEs, and the large isotope anomalies of O 3 and BrO, are the driving force for the variability in the measured Δ 17 O(NO − 3 ) . BrONO 2 hydrolysis is found to be a dominant source of nitrate in the Arctic boundary layer, in agreement with recent modeling studies.