Horizontal transport modelled properties for northern latitudes (> 45°N) ACS MIR HCl detections of MY 35. Left: lowest altitude where the horizontal transport lifetime of HCl becomes lower than the photochemical lifetime (i.e. where horizontal transport can compete with chemistry) in the atmospheric column corresponding to the ACS MIR observation. Squares located at 5 km are used when the horizontal transport lifetime is larger than the photochemical lifetime in the entire column. Right: maximum net flux of HCl resulting from horizontal transport in the atmospheric column where the HCl observation is performed. Squares located at 10⁻⁷ kg/s are used when the maximum net mass flux in lower or equal to zero. In both panels, red dots indicate the observations where we find the largest negative biases between model results and ACS MIR observations in MY 35, corresponding to observations between L_S=140-220°.