Signature of Arctic surface ozone depletion events in the isotope anomaly (Δ17O) of atmospheric nitrate

[摘要] 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) inspring 2004. Covering the polar sunrise period, characterized by theoccurrence of severe boundary layer ozone depletion events (ODEs), our datashow 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), forΔ¹⁷O(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 ofO₃, RO₂ and BrOin the oxidation ofNO during ODEs, and the large isotope anomaliesof O₃ and BrO, are the driving force for thevariability in the measured Δ¹⁷O(NO⁻₃) . BrONO₂hydrolysis is found to be a dominant source of nitrate in the Arctic boundarylayer, in agreement with recent modeling studies.

[学科分类] 大气科学