A system for the detection of components in a region of the atmosphere is disclosed, the system comprising a spectrometer assembly having a detector optically coupled to a optical assembly, the optical assembly receiving incident sunlight from the region of the atmosphere, the optical assembly having a field of view extending from the zenith to below the horizon; means for rotating the spectrometer assembly about a vertical axis; and a processor for receiving data from the spectrometer assembly and compiling data relating to the identity and concentration of components in the region of the atmosphere. A method of monitoring pollutants in a region of the atmosphere comprises providing a spectrometer assembly having a detector optically coupled to an optical assembly having a field of view extending from the zenith to below the horizon; exposing the spectrometer assembly to incident sunlight while rotating the spectrometer assembly about a substantially vertical axis; and processing signals received from the spectrometer assembly to analyse components in the atmosphere. The system and method are particularly useful in monitoring atmospheric pollutants arising from the combustion of hydrocarbon fuels, in particular oxides of nitrogen and/or sulphur. A preferred arrangement comprises a plurality of systems disposed at spaced apart locations and having their scanned regions overlapping.