Methane standards would cut up to ten times more methane and four times more smog - forming pollutants compared to other policy approaches available to EPA, because more sources would be reached. (dotearth.blogs.nytimes.com)
Just weeks ago, it cautioned that a warming climate will also spawn more smog, which is linked to heart disease and respiratory ills. (scientificamerican.com)
The cons: Diesel engines are very durable, which means that very dirty old trucks are still on the road, they generally produce more smog - forming emissions (NOx, PM, etc), they are more expensive than gasoline engines, and they can be noisier and smellier (though recent models have made lots of progress there). (treehugger.com)