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

Hi,
I'm using the MQ-9 grove sensor for a project on indoor air quality with Arduino Uno Wifi.
I'm following the guide from this site:

http://wiki.seeed.cc/Grove-Gas_Sensor-MQ9/

I would have two questions to ask.

  1. What is meant by:'Keep the Gas Sensor in clean air environment'? Can I leave the sensor in my room?

  2. After determining the Rs / R0 ratio, I am unable to determine the concentration in ppm of the 3 individual gases (LPG, CO, CH4) by having the graph at the end of the linked page. Is there a way to determine it for each gas?

I hope you can help me and thank you in advance.

  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)