" City-grown pollution , and ozone in particular , is tougher on country trees , " says Cornell University ecologist Jillian Gregg .
" City-grown pollution , and ozone in particular , is tougher on country trees , " says Cornell University ecologist Jillian Gregg .
" I know this sounds counterintuitive , but it 's true : City-grown pollution -- and ozone in particular -- is tougher on country trees , " U.S. ecologist Jillian Gregg said .