At this time of the COVID-19 pandemic, you would almost forget that there are other reasons to wear a face mask. And that there are places where this has been advisable, if not necessary, for much longer. Living in Asia in large cities, outdoor sports are often problematic due to air pollution, especially for 2.5 µm particles, also called PM2.5. High concentrations of these small particles in ambient air can be harmful and even dangerous to your health. The PM2.5 display presented in this article can be used to monitor air quality.