I also have an AQ-N unit and I had similar questions.
- Modbus register 108 always reads 0 in my case and is unusable. I believe it was meant to report the CO2 sensor reading, if the board had one.
- Modbus register 184 is usable and contains the decoded AQ value from the AQ sensor. When @maurice replied to my question, he kindly provided a link to the AQ sensor model/datasheet. Please see here: AQ-N-LCD - various questions - #2 by maurice. The datasheet contains a detailed explanation of what the value represents and how it’s determined.
Cheers!