Broadband integrated cavity output spectroscopy (ICOS) utilizing an incoherent tungsten lamp as a spectroscopic source is described. This novel approach has been termed W-ICOS. The technique has been applied to make quantitative measurements of Rayleigh scattering by carbon dioxide between 570 and 590 nm and to make measurements of aerosol and atmospheric extinction. Minimum detectable extinction coefficients (kext) made in a 94 cm optical cavity ranged between 3.4 and 35 Mm-1 depending on the level of signal averaging employed. The level of sensitivity achieved should allow measurements on static gas samples and regular, quantitative measurements of the atmospheric extinction coefficient.