MIAMI — Over the last 40 years, North American cars and power plants have gotten cleaner. They spewed far less pollution into the atmosphere, a difference visible by satellites. But a new paper from NOAA published Wednesday in the journal Science Advances suggests that the cleaner air may have had an unintended effect — more hurricanes. Study author Hiroyuki Murakami, a physical scientist at NOAA’s Geophysical Fluid Dynamics Laboratory, said he found a connection between the number of hurricanes and the amount of air pollution in the form of particles called aerosols. “We naturally think it’s …