On average the outdoor air contains about 450 ppm (parts per million) of CO2. This can vary depending on where you live, larger cities may have increased base levels of CO2.
​
The ideal CO2 levels indoors are under 1000ppm.
​
Indoor CO2 levels ideally shouldn't rise above 1500 ppm. However, if they do, you should take the necessary steps to ventilate with fresh air by opening a window, a door or running your HVAC system.
​
CO2 levels above 2000 ppm should be avoided, with longer exposure, headaches, sleepiness, and stagnant, stale, stuffy air. Poor concentration, loss of attention, increased heart rate, and slight nausea are possible.