What PM2.5 Particles Actually Are
Launch library · evergreen read
PM2.5 refers to particles smaller than two and a half microns across, roughly thirty times finer than a human hair. They form from combustion, dust and chemical reactions in the atmosphere, and their small size is exactly what makes them concerning: they are light enough to stay airborne for long periods and travel far from their source.
Size, not just quantity, decides the health impact. Larger dust particles are mostly trapped by the nose and throat, but particles this fine can reach deep into the lungs and pass into the bloodstream. That is why health guidance focuses on this size fraction specifically rather than treating all airborne dust the same way.
Sources are varied and often mundane: wood heaters, vehicle exhaust, industrial processes and even cooking all contribute. Because the particles are invisible individually, air quality monitoring relies on instruments rather than the naked eye, which is part of why published readings matter more than what a sky simply looks like.