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Take a deep breath next time you board a plane at Seattle-Tacoma International Airport.

Chances are, the air will be cleaner.

For most of the jet age, passenger cabins have been cooled by the plane’s own auxiliary-power engine, which burns jet fuel while the plane is serviced at the gate. Or a portable diesel generator was wheeled alongside.

Either way, the exhaust hovered on the tarmac.

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But last month, the airport launched a new “preconditioned air” network that cools (or heats) at a central plant, then pumps treated air through hoses directly into the plane.

So far, 29 gates are using it, and all 73 gates will supply preconditioned air by the end of this year. The active gates include all of Concourse A, which serves mostly United Airlines.

The system reduces fuel consumption by 40 to 100 gallons each layover because the planes don’t have to supply their own energy, said Jonna McGrath, United station manager at Sea-Tac.

Connecting the entire airport should reduce global-warming emissions comparable to taking 8,000 cars off the road, according to the Port of Seattle, which operates the airport.

The $43 million conversion is half-funded by a federal air-quality grant, and half by the gate fees airlines pay to the Port. Airlines expect to save $15 million a year and to recoup their cost within three years.

Considering a jet-fuel cost of around $3 per gallon, “I can save up to $300 an hour,” McGrath said.

The new system “doesn’t really change the air quality in the plane,” McGrath said. But it seems plausible that once all the gates use preconditioned air, the ambient air ought to become cleaner.

Sea-Tac will be the largest airport in the U.S. to supply every gate with preconditioned air, said airport spokesman Perry Cooper.

United is using preconditioned air in several cities, including Houston, Chicago and Denver, McGrath said.

Fifteen miles of pipes connect the chillers and heaters at Sea-Tac to the gates.

Inside the vast “chilling room,” beneath the air terminal’s food court, a pink glycol-water mixture circulates in four 750-ton chillers cooled by electric power, to below 32 degrees Fahrenheit. Alongside them are 16 steel tanks full of ice. Coolant flows mainly through the ice tanks, or directly from the chillers, before it travels to the gates.

Reaching the gate, the coolant next circulates inside a huge box — where outdoor air is being sucked in and chilled by coolant within smaller pipes. The now-cooled air is filtered and pumped to the aircraft.

“It’s like a radiator,” said Elizabeth Leavitt, director of airport planning and environmental services. There’s even a cold mist of condensation that trickles to the pavement.

Seattle is especially fit for preconditioned air because more than 90 percent of the electricity used in central cooling is generated by emission-free, hydroelectric dams. The heating pipes have been hooked to the same steam plant, fired by natural gas, that heats the terminal buildings.

Ironically, Sea-Tac’s antiquated, boomerang-shaped terminal — a byproduct of formerly using an X-shaped runway grid, says Cooper — creates a huge advantage by allowing a relatively short distance to string pipes from the central chilling room to all gates.

This is the latest of several clean-air projects by the Port.

• Rental-car operations were centralized in a new building north of the airport, where compressed-natural-gas shuttles carry arriving passengers to the car center. This reduces some 165,000 vehicle trips per month to scattered rental locations.

• Aviation fuel has been dispensed from hydrants since 2005, reducing the need to drive fuel-tanker trucks on the tarmac.

• Recyclables and garbage are deposited at shared compacting stations near the gates, instead of each airline fetching waste using a fleet of trucks. Therefore, only a couple truck runs monthly need to be made, Cooper said.

• Most cruise ships plug into shoreside power lines at the Seattle waterfront instead of burning diesel to generate internal power while in port.

• The Port’s Clean Trucks program offers partial payment to short-haul truckers to scrap old trucks and buy newer vehicles, for moving containers between Elliott Bay docks and the nearby rail yards. Another round of incentives, as much as $20,000 per truck, is planned next year. Currently, the street-level experience is still that trucks often emit nauseating levels of diesel.

Mike Lindblom: 206-515-5631 or On Twitter @mikelindblom

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