Formaldehyde (HCHO) in air, snow, and interstitial air at Concordia (East Antarctic Plateau) in summer

Abstract : During the 2011/12 and 2012/13 austral summers , HCHO was investigated for the first time in ambient air, snow, and interstitial air at the Concordia site, located near Dome C on the East Antarctic Plateau, by deploying an Aerolaser AL-4021 analyzer. Snow emission fluxes were estimated from vertical gradients of mixing ratios observed at 1 cm and 1 m above the snow surface as well as in interstitial air a few centimeters below the surface and in air just above the snowpack. Typical flux values range between 1 and 2 × 10¹² molecules m^-2 s^-1 at night and 3 and 5 × 10¹² molecules m^-2 s^-1 at noon. Shading experiments suggest that the photochemical HCHO production in the snowpack at Concordia remains negligible compared to temperature-driven air–snow exchanges. At 1 m above the snow surface, the observed mean mixing ratio of 130 pptv and its diurnal cycle characterized by a slight decrease around noon are quite well reproduced by 1-D simulations that include snow emissions and gas-phase methane oxidation chemistry. Simulations indicate that the gas-phase production from CH₄ oxidation largely contributes (66 %) to the observed HCHO mixing ratios. In addition, HCHO snow emissions account for ∼ 30 % at night and ∼ 10 % at noon to the observed HCHO levels.