An enhancement factor of 6 has been achieved for an air plasma terahertz source by applying several compensation and optimization techniques simultaneously. In the laboratory setup, two-color air plasma is induced with an 800nm laser focused through a 100 µm thick beta barium borate (BBO) crystal. A second BBO crystal is used to compensate for spatial and temporal walk-offs, and a dual-wavelength half-wave plate adjusts the 2nd harmonic 400nm polarization to further enhance the conversion efficiency. The authors conclude that marginally higher conversion efficiencies are possible by optimizing the thickness of the second harmonic generation (SHG) crystal.