Diesel fuel is not a "gasoline", even if the article refers to it as such.

And, contrary to the article's claim, it has been some time since diesel has been less expensive than gasoline; and the production capacity of refineries has little to do with it. But, the relative energy values of the gasoline and diesel do. (This is not a function of the types of engines or efficiencies of the engines that use the respective fuels.) Per unit of energy, the prices were comparable for several years, until last year. Then diesel did become more expensive. Why? Due to the added cost of introducing advanced technologies required to drastically reduce remove sulfur from the fuel and so
from products of diesel combustion.

For cleaner air? Yes, but indirectly so. In order to employ technologies to reduce other harmful pollutants from the diesel fuel combustion products, it was necessary to drastically reduce the sulfur which would contaminate the exhaust stream processers. Now diesel engine technologies can be introduced in the US which have been available in Europe for .....oh....5 to 7 years.