Two major industrial fires darkened the skies over Seattle’s Duwamish Valley in recent weeks and added soot and other pollutants to the area with the city’s worst air pollution.
But the city’s Fourth of July fireworks celebrations added more.
Air pollution monitoring stations in South Seattle and Tukwila recorded a spike in levels of fine particulates, or soot, in the 10 p.m. hour Wednesday night. That's when the big Lake Union fireworks show dazzled audiences in person and on TV.
The air monitoring station in South Park showed a smaller pollution spike a few hours earlier, apparently from a fire at a warehouse and auto scrapyard near the West Seattle Bridge.
"We did see much higher levels from in our air monitors in the Duwamish Valley than we did from the warehouse fire, on the order of three to four times higher," said Erik Saganic, an air quality scientist with the Puget Sound Clean Air Agency.
"It adds a burden to a community that already faces quite a few," Saganic said.
Smoke from an even bigger scrapyard fire on a barge on the Duwamish River June 26 could be seen around the city. But the barge fire's soot also was just a fraction of that released by the annual fireworks celebration, according to Saganic.
Seattle Fire Department Lt. Sue Stangel said the barge fire began when the operator of a grappling hook punctured a propane tank hidden beneath the bed of a scrapped pickup truck. She said the cause of the July 4 scrapyard fire was unknown.
"Car fires can have a number of fuel elements to it," Stangel said. "The tires, any of that stuff makes any kind of car fire toxic."
During Fourth of July festivities, pyrotechnics crews shot off more than 10,000 pounds of fireworks, with some shells as big as 10 inches in diameter, from a barge on Lake Union to the oohs and ahhs of thousands gathered at Gasworks Park and elsewhere around the city.
The next morning, around 100 volunteers with Puget Soundkeeper picked up 553 pounds of fireworks casings and miscellaneous party trash from the surface and shores of Lake Union.
"There are bits of nylon rope, rubber bands and plastic pieces in addition to the cardboard," in the fireworks remains, Amelia Apfel with Puget Soundkeeper said in an email. "We certainly don’t get it all so yes, some remains in the lake, sinks and either degrades or becomes a permanent lake fixture."
One of the kayakers pulled an unexploded firework about the size of a volleyball from the lake. A bomb squad from the Seattle Police Department arrived to dispose of it safely.
This year, like most years, the soot and smoke from the fireworks dissipated within a couple hours, Saganic said.
Saganic said nighttime air tends to settle downward as it cools, helping hold pollution near the surface — and people's lungs.
Some years, the air is stagnant enough that the unhealthy pall remains over the city for most of a day. That's long enough to trigger asthma and heart attacks in some people.