Dust particles in the air can negatively influence the well-being of humans. This is why germany and The Netherlands have quite severe limits for dust particles in the air. Even more severe risk is carried by aerosols, liquid particles, that may carry viruses like COVID-19 from one carrier to another. The PPM 2.5 Sensor "senses" if humans are around, or where in the room you are bound to enter. Just send the "mBot Guardian" ahead prior to entering the room. He will alert you with red lights and alarming beeps if the air quality is out of limits, or a lot of potentially harmful aerosols fill the air.