Jennifer Duggan is with the Environmental Integrity Project, which represents the plaintiffs.
"The groups want EPA to take action to revise these emission factors so that pollution from refineries and chemical plants are actually, you know, are accurate, and they are accounted for."
Duggan says a study at Shell's Deer Park refinery found that emission factors can undercount volatile organic compounds, or VOCs.
"They found that the emission factors can undercount toxic emissions by a factor of 132. They measured one tank that emitted 20 pounds of VOCs per hour, and the emission factor estimate would have given the result of two pounds per hour."
Former Houston Major Bill White formally petitioned the EPA five years ago to modernize their calculations.
The EPA says it's reviewing the lawsuit.