America’s air monitors are disappearing. So is your power to expose polluters.

The nation's public air-monitoring network has been shrinking for decades. Federal grants for it have fallen more than 35 percent over 20 years, adjusted for inflation, and the number of government monitors has dropped by nearly half. The equipment that's left often sits far from major industrial sources and misses many of the chemicals those sources release. In four states studied — Louisiana, Ohio, Kentucky, and West Virginia — most of the largest polluters emit a top chemical that no nearby public monitor even measures.

As public monitoring has weakened, some communities have turned to low-cost air sensors they can run themselves. But lawmakers in Louisiana, Ohio, and Kentucky have passed bills, backed by chemical and manufacturing trade groups, that block regulators from using this community-collected data in enforcement actions unless it meets EPA-approved standards. Similar bills have been introduced in West Virginia but haven't passed. Supporters say the rules ensure data is scientifically reliable; critics say they strip residents of one of the only tools they have to document pollution near their homes.

Meanwhile, some states have gone the other direction. California, Colorado, and Texas have funded better monitoring equipment, including devices installed at industrial fencelines, in communities most affected by pollution.

For homeowners, the practical takeaway is that whether you can find reliable, real-time information about air quality near your house depends heavily on your state. If you live near industrial facilities, it's worth checking what monitoring — public or community-run — exists nearby, and what your state currently allows that data to be used for.