Whenever ships dock near her waterfront house in Stockton, Calif., Sherry Shields hides indoors. She says she can't relax in her yard. She won't let her grandchildren play outside. The smoke billowing from the ships' exhaust stacks, she says, makes the air hard to breathe. "Many times you can see the black plume coming," says Shields, whose citizens group is suing to block expansion of the nearby port on Stockton's inland waterway. "It's unconscionable that this is happening next to homes." From fishing skiffs to supertankers, boats and ships around the USA are belching out harmful pollutants that cloud the...