Abstract. Fast and reliable methods for the detection of atmospheric trace species are needed for near-real-time applications including volcanic hazard avoidance. One common approach using hyperspectral instruments is to measure the difference in brightness temperature between a small number of target sensitive and background channels to determine the presence of the target species. Although fast and robust, current brightness temperature difference methods do not fully exploit the spectral range and resolution of hyperspectral instruments, and the noise associated with the measurements remains high. In this paper, we describe a way to make full use of the spectral information from hyperspectral sounders allowing the presence of the target species to be determined with much better sensitivity in near-real-time if required. The technique is demonstrated using the MetOp Infrared Atmospheric Sounding Interferometer considering two case studies: (a) the detection of sulphur dioxide from the eruption of the Kasatochi volcano in Alaska in August 2008, and (b) the detection of ammonia emissions related to agriculture over Southern Asia in May 2008. The performance of this method is compared against that of existing brightness temperature difference methods. It is found that the sensitivity of the detection of these trace species is improved by up to an order of magnitude.