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  • Diagram showing size comparisons for PM particles.
    Rights: EPA, United States Environmental Protection Agency Published 18 June 2008, Updated 10 September 2019 Size: 1.2 MB Referencing Hub media

    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.

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