Chemical anisotropy of the cosmic microwave background radiation

It is shown how the large-scale inhomogeneous distribution of chemical elements in the primordial medium contributes to temperature fluctuations of the cosmic microwave background radiation (CMB). The magnitude of the chemical anisotropy of the CMB, which is sensitive to the absolute and relative abundance of chemical elements at the time of decoupling, is compared with the primary Sachs-Wolfe anisotropy of the CMB in the baryon acoustic oscillations scale, which shows that the two effects are of similar importance.