` ` We still have a long way to go , '' says American Lung Association official . NASA data show substantial reduction in nitrogen dioxide . It is one of six common air pollutants for which the Environmental Protection Agency has set limits . NASA scientists recommend reductions to more - efficient cars , and emissions cuts . Nitrogen dioxide is separate from greenhouse gases , which were n't included in this report .
` ` We still have a long way to go , '' says American Lung Association official . NASA data show substantial reduction in nitrogen dioxide . NASA scientists recommend reductions to more - efficient cars , and emissions cuts . Nitrogen dioxide is separate from greenhouse gases , which were n't included in this report .