On the short 3D animation below we can see what are the actual sizes for the PM2.5 and PM10 particles in comparison with a pin, a human hair and a sea salt grain. Pay attention on how tiny is the PM2.5 particle. Now, imagine these particles penetrating deep inside your lungs and the damage they can cause.
See The Air 
Very Cool Graphic!! I also like that is shows the difference between PM 2.5 and PM 10.
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If a picture is worth a thousand words, a video is worth a hundred thousand. Excellent illustration.
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