The outside air quality (on the bottom of the app's home screen) comes from an air quality monitoring station near you. These monitoring stations are most often run by government environmental agencies. We show the outside air quality if the there's a station within 9 miles (15km) of you. Usually, the value you see on the tracker outside and the value reported by the nearest monitoring station will be similar. You may notice that these monitoring stations will sense something different from what your own tracker senses outdoors, due to air quality microclimates. There could be an industrial plant closer to the monitoring station than to you, or there might be an exhaust-filled highway nearby to your location.
If you believe that the value coming from your tracker is egregiously wrong, then please refer to this Wynd Help Center article.