what does NO (PPM) mean on californias smog test? what does it measure? I...

Nitric oxide or nitrogen monoxide is a chemical compound with chemical formula NO. This gas is an important signaling molecule in the body of mammals, including humans, and is an extremely important intermediate in the chemical industry. It is also a toxic air pollutant produced by cigarette smoke, automobile engines and power plants.

Tune up, new catalytic converter, etc. none of it worth doing if you keep passing the test.