what is the polarization of this wave ?

Assuming a_y and a_z refer to the unit vectors along the Y and Z axis and that E_10 and E_20 are numerical constants, your E field would be a linearly polarized.

The axis of polarization would be a slant line in between the Y and Z axis. (the angle would be dependent on the ratio of E_10 to E_20).

The sin(...) component just serves to indicate oscillation (and direction of travel) for this wave.