The EXSCALABAR instrument was developed by the Met Office (Exeter, UK), which can be operated in both the laboratory and from the UK atmospheric research aircraft (FAAM BAe-146). The instrument uses cavity ring-down spectroscopy (CRDS) to measure the dry aerosol extinction at 405 and 660 nm and photoacoustic spectroscopy (PAS) to measure the dry aerosol absorption coefficient at the wavelengths of 405, 515 and 660 nm wavelengths.