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

• Published in: Atmospheric Chemistry and Physics
• Main Authors: Morin, S., Savarino, J., Bekki, S., Gong, S., Bottenheim, J. W.
• Other Authors: Université Pierre et Marie Curie - Paris 6 (UPMC)
• Format: Article in Journal/Newspaper
• Language: English
• Published: HAL CCSD 2007
• Subjects: [SDU]Sciences of the Universe [physics]; Arctic; Nunavut; Canada
• Online Access: https://hal.science/hal-04110213; https://doi.org/10.5194/acp-7-1451-2007

International audience 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.