mq sensors

I know there have been tons of discussions about mq gas sensors too many diy step by step instructions but I couldnt find if data of difference in concentration of gases in fresh air and in home.

What I mean is if I know approximate CO concentration in fresh air I can calibrate my sensor in that enviroment then use it. But if I will take concentration in fresh air and concentration in my home I will have value to calibrate sensor in home in future knowing difference (fresh air calibration-home calibration) and can apply that difference in future. There will be no need to take sensor outside to calibrate again.

Am I missing something or I`m in right direction?

There should not be a source of CO inside your house. So the concentration in your house should be about the same as outdoors.

To properly calibrate your sensors, you have to purchase bottles of gas with a known concentration of each gas. This can get expensive. Cheaper calibrations are possible for some gases, particularly when you can produce a known amount of the gas through electrolysis. It's easy to count amps and seconds for an electrolytic cell.

Thanks for reply I was thinking that way till start reading about CO levels at home from governmental websites .

"Average levels in homes without gas stoves vary from 0.5 to 5 parts per million (ppm). Levels near properly adjusted gas stoves are often 5 to 15 ppm and those near poorly adjusted stoves may be 30 ppm or higher."

So it cant be 0. Average concentration in my area is 0.22ppm lets say I read resistance value at current temperature and fixed results. Then I bring sensor home and tested again got resistance value which differs from the one outside and calculated ppm for current gas from resistance value. So next time if I want to calibrate the sensor again there will be no need to take it out again if I know what is current level outside then can measure only whats inside home substract one from another and calibration will be done.

Am I right?