Contrary to most people' s idea, the air in Coastal cities can be far from fresh and healthful, said a report recently published. University of California Professor Mark Thiemens led the research team. His team. report blames ships that release dirty smoke by burning low-cost, high-sulfur  fuel. They directly measured smoke released from a ship. They also tested air at the end of the Scripps Pier  .The area is just north of San Diego, which is both a major city and port. The Scripps Pier is also close to waters with heavy shipping traffic and the city of Los Angeles. Los Angeles has the third largest port in the world. Primary sulfate  is produced when a ship burns fuel called bunker oil. Bunker oil contains a Large amount of sulfur. Most sulfur released by ships burning bunker oil is a gaseous pollutant--sulfur dioxide. After a time, sulfur dioxide becomes sulfate in the atmosphere. The researchers say this primary sulfate may be  only a small part of what ships produce. Professor Thiemens said no one had really expected that ships would be responsible for so many , particulates  .He said the extremely small particles ( )are especially threatening. They measure only one and one half microns in size., A micron is one millionth of a meter. The researchers say the particulates can travel long distances because they stay in the atmosphere longer than other pollutants. Professor Thiemens noted that the air of Los Angeles influenced air quality in San Die -go. That distance is almost 180 kilometers.   , Primary sulfur particulates can also threaten human health. When people breathe, the particulates stay in their lungs. Other scientists have said that up to 60,000 people around the world die each year from dirty ship smoke. Other gaseous pollutants from ships include nitrogen oxide and carbon dioxide. Earlier this year, a United Nations' report said gases from ships produce more than one billion tons of carbon dioxide every year. Ships are not governed under the Kyoto Protocol, the agreement that establishes limits for gases linked to climate change. But international rules requiring ship fuels that burn cleanly are to become effective in 2015. What is the main idea of the passage?
Coastal cities are ideal places to live in. The air quality in coastal cities is worrying. Cleaner-burning fuels are welcome in ships. The world's oceans' ecosystem is far from satisfactory.