Tuesday morning, the Supreme Court will hear arguments over what the Environmental Protection Agency terms the “good neighbor” rule. In this case, geniality is measured in toxic pollution—specifically, in industry-heavy Midwestern states and coal-dependent southern states’ willingness to rein it in for the sake of Northeasterners who are suffering downwind.

The prevailing wind patterns in the United States are northeasterly, making New England the “tail pipe” of the country where air quality is concerned, in the words of John Walke, clean air director at the Natural Resources Defense Council. In the city of New Haven, Connecticut, for example, 93 percent of the ozone pollution is coming from other states, leading Connecticut Governor Daniel Malloy to tell The New York Times that Appalachia and the Rust Belt “are getting away with murder…only it’s in our state, not theirs.” Throughout New England and the mid-Atlantic, between 70 percent and 98 percent of ozone air pollution is coming from upwind regions. Governors of the affected states say no matter what regulations they impose or clean-up technology they install in their power plants, the air quality on the East Coast remains intractably poor.

In 2008, the U.S. Court of Appeals for the District of Columbia ruled that the EPA was required by law to write a set of regulations for cross-state pollution, under the Clean Air Act, which would be stricter than the policies employed by the administration of President George W. Bush. But when President Barack Obama’s EPA produced its Cross-State Air Pollution Rule, the same court struck it down as excessively harsh on the eve of implementation in early 2012. Tuesday, the court will attempt to make sense of these warring precedents; the justices have allotted 90 minutes for the arguments instead of the usual 60, suggesting the significance they attribute to the case.

Eight Northeastern states on Monday petitioned the EPA to include the upwind offenders in a set of federal ozone pollution regulations that since 1990 have held New England to higher standards than most other regions—in part because of its history of dirty air. But Walke said if the Supreme Court overturns the EPA’s rule, the relief provided by the petition would be a “plan B-minus” in comparison. In the map below, the Environmental Defense Fund, a D.C. think tank, has mapped the number of lives the Cross-State Air Pollution Rule would save each year, in both upwind and downwind states. In aggregate, they calculate it would prevent up to 34,000 deaths from exposure to pollution in a year. In Texas, for example, pollution from plants in the state’s south and west is contributing to 1,704 deaths a year at home—and thousands more in states along the path of the prevailing winds.

While the Supreme Court hears arguments on one rule, the D.C. Circuit court will hear an industry challenge to another law written by the EPA, the Mercury and Air Toxics Standards it released in late 2011. Together, EPA calculates the cross-state law and the mercury and air toxics law could save up to 46,000 lives a year as soon as 2016.