Guardian: Thousands of merchant ships chug in and out of south Florida’s bustling ports each year, bringing boatloads worth of economic benefit to the region. They also deliver a more dangerous cargo: airborne pollution from giant diesel engines that can sicken coastal residents, or even shorten people’s lives. A study by the National Oceanic and Atmospheric Administration (Noaa), the most comprehensive yet, found that commercial vessels - freighters, tankers and cruise ships - generate …