New Estimation of the NO<sub>x</sub> Snow‐Source on the Antarctic Plateau
Albane Barbero, Joël Savarino, Roberto Grilli, Camille Blouzon, Ghislain Picard, M. M. Frey, Yaoxian Huang, Nicolas Caillon
Abstract
Abstract To fully decipher the role of nitrate photolysis on the atmospheric oxidative capacity in snow‐covered regions, NO x flux must be determined with more precision than existing estimates. Here, we introduce a method based on dynamic flux chamber measurements for evaluating the NO x production by photolysis of snowpack nitrate in Antarctica. Flux chamber experiments were conducted for the first time in Antarctica, at the French‐Italian station Concordia, Dome C (75°06'S, 123°20’E, 3233 m a.s.l) during the 2019–2020 summer campaign. Measurements were gathered with several snow samples of different ages ranging from newly formed drifted snow to 6‐year‐old firn. Contrary to existing literature expectations, the daily average photolysis rate coefficient, , did not significantly vary between differently aged snow samples, suggesting that the photolabile nitrate in snow behaves as a single‐family source with common photochemical properties, where a = (2.37 0.35) × 10 −8 s −1 (1 ) has been calculated from December 10 th 2019 to January 7 th 2020. At Dome C summer daily average NO x flux, , based on measured NO x production rates was estimated to be (4.3 1.2) × 10 8 molecules cm −2 s −1 , which is 1.5–7 times less than the net NO x flux observed previously above snow at Dome C using the gradient flux method. Using these results, we extrapolated an annual continental snow sourced NO x budget of 0.017 0.003 Tg N y −1 , 2 times the nitrogen budget, (N‐budget), of the stratospheric denitrification previously estimated for Antarctica. These quantifications of nitrate photolysis using flux chamber experiments provide a road‐map toward a new parameterization of the product that can improve future global and regional models of atmospheric chemistry.