If you are thrifty as most are , placing a few layers of bounty paper towel in front of there filter will catch most of the dirt and make your $12 filter last much longer . Toilet paper is also a good choice . If you try to put it inside in front of the heppa filter the cover may not close or you could crush there filter , use common sense please.
https://www.amazon.com/BROAD-AirPro-Electrical-Purifying-Respirator/dp/B088BL2TLC