Azimuthal velocity deviation at the midplane , expressed in terms of the radial pressure gradient parameter η (Equation (35)). The black dashed and solid lines show η before vapor injection and after the steady state is reached, respectively. The red lines show the vapor fraction corresponding to the y-axis on the right. The blue arrows indicate the position of the midplane snowline (r_snow,mid). A reduction of η at the snowline region strengthens solid pileups and is conducive to planetesimal formation by streaming instability and planet formation by pebble accretion.