The atmosphere affects on the propagation of optical radiation by different ways. This influences the performance of Electro Optical systems. FOI, earlier FOA, has carried out aerosol measurements during many years in order to characterise Swedish conditions. The reason was that IR transmission models (mostly American) underestimated the IR attenuation compared to IR measurements. Results from a multi channel transmissometer OLA (Optical Link in the Atmosphere), have also been used to build an aerosol model earlier. However, there are reasons to check alternate models, for one thing to simply the previose models and that further measurements have been done. Two simple models to approximate aerosol extinction coefficients (alpha alpha) have been described in this report. The models estimates alpha alpha from the weather parameters visibility, temperature, and wind speed. Transmission which was approximated by the models has also been compared with transmission calculated with the MODTRAN model for different weather situations. One conclusion drawn from the analysis results shows that there are a larger amount of course aerosol particles at the measurement site, than the size distribution used in MODTRAN proposes. In general the Maritime model in MODTRAN seems to give a reasonable good result in the visible and IR wavelengths up to about 4 micrometers. However, at longer wavelengths also the Maritime model underestimates the aerosol attenuation with a factor of 2-4 at 10 micrometers.