Yale Environment 360: More than 90 percent of Europeans living in cities are exposed to harmful levels of air pollutants, according to a new assessment from the European Environment Agency. Concentrations of ground-level ozone, or smog, pose a danger to 97 percent of city populations, and levels of fine particulate matter (particles with a diameter less than 2.5 microns, known as PM2.5) exceed European standards for 91 to 96 percent of city-dwellers and that's with European standards for both pollutants exceeding World...