First, we should define where poor air occurs. We assume that the air quality indoors is never better than outdoor air.

We wake up in the morning in a room where, in the worst case, all windows are closed, or a fan or air conditioner merely circulates the air. We leave the house, drive to work with closed windows in the car, or, in the worst case, use public transport.

At the workplace, most windows are usually closed or at least not open enough to provide sufficient fresh air for all employees. A glance at the ventilation system does not reveal whether it supplies fresh air or just circulates indoor air.

In the evening, we get back into the car or the bus. Maybe we go shopping – again in indoor spaces with unknown air quality.

Even if one of these places offers better air quality, we are still exposed to poor indoor air quality most of the time. In the short term, this may not be a problem, but in the long term, we are exposed to this situation every day for a lifetime.

Of course, there are holidays when we spend time outdoors. However, this is usually among many people in amusement parks or at events – places where air quality is impaired simply by the number of people present.

Even if we manage to breathe good air in the forest on some days, we still mostly live in an environment with unnaturally poor air. The comparatively short time spent in fresh air – assuming the surrounding air is not already too polluted – is minuscule.

Even those who pay attention to good fresh air supply and lifestyle during the day are still exposed to increased pollutant concentrations most of their lives.