The similar values of the radiation pressure incident on the BLR, and the pressure of the gas at BLR, suggest the gas is being compressed by the incident radiation pressure. This radiation pressure compression (RPC) may also provides a natural solution to the overionization problem for the BAL outflow.
How can one test this solution?
Furthermore, what is the source of gas which forms the BLR?
What are the expected properties of a wind formed by the ablation of the RPC BLR gas?
Can RPC ablation explain the low fraction of LBALQs?
Can RPC ablation explain a smooth outflow in velocity space, yet highly clumped in real space?
More generally, how can one tell that an outflow is driven by radiation pressure?