Right but specifically solid particles in the air, not just gasses (CO2, NOX, etc.).

For example smoke and soot from combustion or dust particles from tires and brakes.

Particulate matter is relatively large particles, so far as air pollution goes. Think things like soot or smoke, rather than specific chemicals. Burning wood and coal produces far more particulates than, say, natural gas or gasoline-gas.

They're not necessarily large, and the worst for humans is small particulate which gets into the bloodstream through lungs, PM2.5.

https://www.health.ny.gov/environmental/indoors/air/pmq_a.ht...

Breathing in unhealthy levels of PM2.5 can increase the risk of health problems like heart disease, asthma, and low birth weight. Unhealthy levels can also reduce visibility and cause the air to appear hazy.

Outdoor sources include vehicle exhaust, burning wood, gas and other fuels, and fires. Particle pollution can also travel long distances from its source; for example from wildfires hundreds of miles away. Outdoor particle pollution levels are more likely to be higher on days with little or no wind or air mixing.

I agree with everything you wrote. I meant to contrast them with "chemical" air pollution, and 2.5 μm is much larger than a molecule!

Yes, it's associated with cancer, heart disease, and dementia.

Sibling comments are good. I'll add that the biggest concern is PM2.5 (particulates smaller than 2.5 micrometers). They're thought to be responsible for 70,000 excess deaths in the U.S. annually, more than homicides or drug overdoses: https://www.stateofglobalair.org/health/pm