In wireless optical communication system, communication is obtained between receiver and transmitter in free space. The major challenge for wireless optical communication system is the free space atmospheric attenuation and scattering caused by Scintillation and aerosol particles (Rain, fog, drizzle and haze). Analysis has been done for the statistical data and then compared with real time data to obtain the refractive index variation due to atmospheric attenuation which cause high impact on wireless optical link design.