Aerosol light scattering and atmospheric transmission data taken at Mauna Loa Observatory show seasonal variations that are strongly correlated and in phase. Total ozone above Mauna Loa is also in phase but accounts for only about 20% of the seasonal variation in atmospheric transmission while aerosols account for the other 80%. Total precipitable water vapor above Mauna Loa is out of phase with atmospheric transmission and cannot account for its seasonal variations. Long-range atmospheric trajectory analyses indicate that tropospheric transport of aerosols from the direction of the Asian continent is most likely responsible for the seasonal variations in atmospheric transmission and aerosol optical properties.