In situ balloon‐borne measurements of HNO 3 and HCl stratospheric vertical profiles influenced by polar stratospheric cloud formation during the 2005–2006 Arctic winter

Abstract : [1] Within the context of the Envisat satellite validation, the Spectromètre InfraRouge par Absorption de Lasers Embarqués (SPIRALE), balloon‐borne infrared spectrometer was flown in the Arctic stratosphere (Kiruna, Sweden; 67.6°N, 21.6°E) in January 2006. In situ vertical profiles of O 3 , N 2 O, HNO 3 , and HCl were obtained between 13 and 27.3 km. The Stratospheric and Tropospheric Aerosols Counter (STAC) was mounted on board, allowing in situ characterization of the vertical particle distribution at six values of radius between 0.2 and 1.0 mm. Complex structures were observed in both HNO 3 and HCl vertical profiles with very low values in the 20.5–22 km layer and simultaneously thin layers of clouds were observed below the HNO 3 depleted layer. We used correlations of N 2 O:HNO 3 and O 3 :HNO 3 to characterize these layers and a model approach to investigate the processes involved. It appears that denitrification and renitrification processes have been captured that were linked to the formation of a polar stratospheric cloud. Several tests using different nitric acid trihydrate (NAT) nucleation rates in the model were performed to obtain the best agreement between microphysical and chemical results and measurements. Best results were obtained with a nucleation rate independent of temperature.