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

Abstract

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.