A new study finds that air pollution is dropping around Puget Sound ports, which have long been a significant source of emissions that increase health risks.

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The air is generally getting cleaner around Puget Sound ports, which over the decades have been a significant source of pollutants that increase the risk of respiratory problems and cancer.

A new report finds that seven different air pollutants declined by amounts ranging from 9 to 97 percent in 2016 compared to 2011.

The improvements result from a mix of voluntary investments in greening port operations and new regulations that require lower emissions and cleaner fuels, according to a report scheduled for release Thursday by the Puget Sound Maritime Air Forum.

But those efforts, over the past five years, didn’t do much to change greenhouse-gas emissions — mainly carbon dioxide. These fossil-fuel emissions, which scientists say are driving climate change, have declined by 1 percent since 2011.

The report covers a broad area, tracking pollutants in the U.S. portion of the international airshed formed by the Puget Sound and Georgia Basin.

The reports uses models — rather than air monitors — to estimate emissions from a range of sources including cargo ships, harbor and recreational vessels, port equipment and trucks that deliver and take away freight.

The report is developed by a partnership of ports, government agencies and businesses. It notes that the air has benefitted from International Maritime Organization regulations that took effect in 2015 requiring cargo ships to use lower-sulfur fuels within 200 miles of the U.S. coasts.

That is the main reason emissions of sulfur dioxide, a pollutant that can make breathing more difficult and aggravate asthma, plummeted by 96 percent between 2011 and 2016 in the study area.

Those rules also helped drive down emissions of particulates, which can damage the lungs and heart. Three different types of this pollution each declined by at least 60 percent, according to the estimates in the study.

Environmental Protection Agency regulation also has played a role in improving the port’s air quality. During the past two decades, the agency has required dramatic changes to truck, train and ship engines and fuel sources as more information revealed the significant health dangers associated with diesel exhaust.

In 2007, after a two-year study outlined just how dirty Puget Sound’s marine-transportation system was, the Puget Sound Clean Air Agency and the ports of Seattle, Tacoma and Everett, helped by EPA grants, set out to make reductions faster than required by law.

One part of that effort has been to increase the use of electricity. Two of Seattle’s three cruise-ship terminals, for example, are outfitted with plug-ins to electric grid, so the vessels don’t have to generate power by idling while moored.

The new study shows one pollutant — carbon monoxide — bucked the downward trend, increasing by 9 percent from 2011 to 2016. That was largely due to an increase in activity by recreational boats and harbor vessels, according to Graham VanderSchelden, environmental project manager for The Northwest Seaport Alliance.

The strong maritime activity also makes it hard to achieve big reductions in greenhouse gases, according to Paul Meyer, a Seattle port official.