Winix air quality sensors (at least the ones I have) measure volatile organic compounds (VOCs), which is a little ironic since HEPA purifiers do little to remove VOCs from the air.

Some other air purifiers like Coways measure particle pollution.

Winix and many other brands can be equipped with activated charcoal filters which do absorb VOCs.

  For consumers looking for a way to remove VOCs in their homes and offices, 
  Kroll adds, “air cleaning using activated carbon filters, a tried-and-true 
  technology that doesn't rely on chemical reactions, is still the way to go.”