They will have to emit less carbon monoxide and fewer chemicals that cause smog.

It just generates a finely-dispersed catalyst that will cause smog to form if the necessary pollutants are present in the atmosphere.

This is a rating for vehicle tailpipe emissions of those pollutants that cause smog and other local air pollution.

These processes have already shown more success than other approaches in reducing emissions of pollutants that cause smog.

All but the smallest are allowed to emit more gases that cause smog per mile than cars.

Nitrogen was also regulated by the 1990 law because it causes smog, a serious health hazard.

But the ranges into which vehicles fall give an idea of their relative contribution to pollution that can cause smog.

This year, for instance, many states failed to show how they would reduce chemicals that cause smog.

They also claimed this causes smog, acid rain, and different respiratory disease.

Illegally created wildfire causes heavy smog around Indonesia's neighbour countries.