GROVE - GAS SENSOR(MQ-9) [CALCULATE PPM]

Other Hardware Sensors
2
  1. Yes. clean air means normal working environment (no 'gas')
  2. No. The sensor doesn't tell which gas is present.

You will find several posts relatetd to MQ7,MQ9 sensors. (some code too)
http://forum.arduino.cc/index.php?topic=208258.17