Measure benzene with an Arduino
If the sensing resistance would be 100kOhm, what would be your verdict? CO2? NH4 in somewhat less concentration?
This sensor measures several gases, so it could be anything!  

So, either pick a sensor that solely measures benzene (no idea if it exists) or pick a few more different sensors that e.g only measure alcohol and NH3 and another that only measures NH3 and CO2 etc and make a kind of truth table to determine the real gas based on the values of all these sensors.

(Above sensor examples are illustrative, I don't know by heart what combinations there are)
Quick search on internet shows e.g. CJMCU-4541 would be a candidate to exclude CO / NO2 / H2 / NH3 / CH4 etc.