Each state sets limits of nitrogen oxides (NOx) from emitting past certain levels out of your vehicle. However, requirements, frequency, and circumstances for SMOG testing vary wildly between states.

A bill currently in committee in the California State Assembly would allow some classic car owners to pay $200 to waive the state's smog check after meeting some other criteria. If a bill ...

Decreased visibility caused fatal collisions of cars and buses; polluted air would spread to the farms beyond the city and damage entire crops in a few hours. It would take years for scientists to ...

home of the strictest car emissions regulations in the U.S., cars produced before 1976 do not need to undergo smog testing. California State Senator Dean Florez has proposed legislation that would ...

Rising smog in Bangkok linked to car emissions, with authorities aiming to reduce private car use to curb pollution ...