In the classroom we measured 1,35 ppm of CO, but what does that mean?

We found a simple scale to realize the quality of our air:

We translated these data in english from http://www.centreantipoisons.be/monoxyde-de-carbone/le-monoxyde-de-carbone-co-en-d-tail/quelles-sont-les-concentrations-toxiques-de

To have the pourcentage, you divide the level in ppm by 10⁴ .

Below 200 ppm, there is no real danger but normally in a non polluted area, the CO level is around 0.2 ppm. As we can see, our air is already quite polluted.