When only two substances, in chemical equilibrium with each other, are responsible for all absorption in a wavelength region, there must exist at least one wavelength in the spectrum of this region where the absorption coefficient will be independent of the ratio of the concentrations of the two substances. This wavelength is called as the isosbestic point, or point of equal absorbance. Such points can also exist in the extinction spectra where at a particular wavelength the extinction coefficient becomes independent of solution concentration. Mie theory has been applied to compute such extinction coefficients. This paper shows the occurrence of isosbestic points in the extinction spectra of liquid droplet aerosols of sizes ranging from 0.1 μm to 10 μm and comprising several concentrations each of hydrochloric, nitric, sulfuric, and orthophosphoric acids in water. Such isosbestic points can serve as reference wavelengths for aerosol spectrometry and also for estimation of liquid content in haze, fog, and nonraining clouds. ¿ 1997 American Geophysical Union