Easy.... atmospheric haze/convection currents... Give us something harder!
Haze causes issues in the area of terrestrial photography, where the penetration of large amounts of dense atmosphere may be necessary to image distant subjects. This results in the visual effect of a loss of contrast in the subject, due to the effect of light scattering through the haze particles. For these reasons, sunrise and sunset colors appear subdued on hazy days, and stars may be obscured at night. In some cases, attenuation by haze is so great that, toward sunset, the sun disappears altogether before reaching the horizon.
Haze can be defined as an aerial form of the Tyndall effect therefore unlike other atmospheric effects such as cloud and fog, haze is spectrally selective: shorter (blue) wavelengths are scattered more, and longer (red/infrared) wavelengths are scattered less. For this reason, many super-telephoto lenses often incorporate yellow filters or coatings to enhance image contrast. Infrared (IR) imaging may also be used to penetrate haze over long distances, with a combination of IR-pass optical filters (such as the Wratten 89B) and IR-sensitive detector.
If I am wrong, and I doubt I am (and I am rarely ), then my next guess is filters, but you would have seen this on all photos. My 3rd guess is that you used olive oil to clean and lube your lenses, but I highly suspect that just isn't the case. I can tell you that doesn't work. The lenses turn easier, but the IQ is never the same.