On Tuesday, a new survey of air emissions showed the most dangerous type of pollution associated with the Puget Sound maritime industry — the tiny toxic particles found in diesel exhaust — had declined 16 percent since 2005.

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Five years ago, environmental regulators discovered that nearly a third of the worst air pollution around Puget Sound was linked to the region’s marine system.

Tugs, ferry boats, oceangoing vessels and the trucks, trains and forklifts that ferry goods to and from container ships made communities around the region’s ports among the dirtiest places in the state.

But they’re improving fast.

On Tuesday, a new detailed survey of air emissions showed the most dangerous type of pollution associated with the maritime industry — the tiny toxic particles found in diesel exhaust — had declined 16 percent overall since 2005.

Tougher federal standards on fuel and engine types — combined with incentive programs adopted by agencies such as the Port of Seattle — are dramatically reducing air pollution across the region’s maritime industry.

The toxic exhaust from heavy trucks is down more than 50 percent, while exhaust from trains serving the ports is down a quarter. Diesel emissions from oceangoing ships — far and away the single dirtiest sector of the shipping industry, accounting for more than 60 percent of the marine industry’s air pollution — are down 16 percent.

“Federal regulations have helped, but we set goals to go way beyond that and we are,” said Stephanie Jones Stebbins, director of seaport environmental planning at the Port of Seattle.

For the past decade, the Environmental Protection Agency (EPA) 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. Chronic exposure can inflame the lungs, lead to heart disease and increase the risk of cancer, along with other significant health problems.

And Washington already has higher asthma rates than the nation at large.

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

EPA and the state offered grants to tug companies to help them re-power boats with cleaner-burning engines. The ports of Seattle and Tacoma subsidized fuel costs for container vessels that voluntarily used fuel lower in sulfur than the EPA required.

Two of Seattle’s three cruise-ship terminals now allow ships to plug into the electric grid rather than idle while on shore. The Port of Seattle and other agencies offered cash incentives for truckers to trade in old vehicles for newer ones with cleaner-burning engines.

The Port of Seattle has spent $5.7 million on these and other programs to reduce air emissions. And even potential critics acknowledge those efforts have been effective.

“This is more than just people responding to new regulations,” said Renee Klein, president of the Pacific Northwest chapter of the American Lung Association. “I’m not sure this level of change would be happening in other parts of the country.”

Certainly, not all the news is good. Throughout the region, pollution from smaller harbor vessels — such as tugs, ferries and fishing boats — actually climbed, in part because the number of vehicles has risen more than 10 percent.

Meanwhile, as overall emissions of carbon dioxide, a greenhouse gas that contributes to climate change, dropped by nearly 100,000 tons a year, those harbor vessels added an additional 31,000 new tons of carbon dioxide annually.

Some reductions in emissions also are clearly the result of decreased traffic through the ports as a result of the recession. But the small dip in goods being shipped through the ports can’t account for the significant reductions.

In the five years since officials learned that the maritime industry was responsible for 29 percent of the region’s dirty diesel exhaust, there also have been rule changes that should reduce air pollution from buses, trucks, motorcycles and other vehicles not associated with the ports.

Since an exhaustive study of those emissions won’t be completed until sometime next year, no one can say whether the maritime industry’s contribution, as a percentage, has changed, nor how much.

Jones, at the Port, said that’s OK. If the percentage of the problem attributed to ports still remains high, that means air pollution from other sources around the region dropped substantially “and that would mean the air’s that much cleaner.”

Craig Welch: 206-464-2093 or cwelch@seattletimes.com.

On Twitter @craigawelch.