Ground-based measurements of halogen oxides at the Hudson Bay by active longpath DOAS and passive MAX-DOAS

[1] Intensive field measurements were carried out on the southeast coast of the Hudson Bay (55°N, 75°W) in spring 2001. The study focussed on reactive halogen chemistry and ozone/mercury depletion in the Hudson Bay region/Canadian lower Arctic. Several events of enhanced bromine oxide (BrO) coinciding with ozone depletion in the boundary layer (BL) were simultaneously measured by active longpath differential optical absorption spectroscopy (LP-DOAS) and passive multi axis differential optical absorption spectroscopy (MAX-DOAS). Significant differences in intensity and duration of ozone depletion events compared to high latitudes can be explained considering the daily alternation of daylight/nighttime which prevents complete ozone depletion within one day. First simultaneous measurements of active LP-DOAS and passive MAX-DOAS were carried out and compared. While LP-DOAS monitored precise concentration values near the surface, MAX-DOAS also captured BrO layers elevated from the surface which could not be seen by LP-DOAS.