![Diagram showing size comparisons for PM particles.](http://static.sciencelearn.org.nz/images/images/000/001/869/full/pm2.5_scale_graphic-color_2.jpg?1674167007)
Particulate matter (PM) is made up of liquid droplets and solid particles fine enough to be suspended in the air. The smaller the particle the deeper it can travel into a person's lungs. Here particulate sizes are compared to the width of a human hair.