DULUTH - Grandma's Marathon organizers lose sleep over heat, humidity and wind, but air quality rose to prominence this week when wildfire smoke lingered over Duluth, triggering an air-quality alert just three days before the race.

"Yesterday would have been a tough day to hold a marathon," Zach Schneider, spokesman for Grandma's Marathon, said Thursday.

The marathon is the city's biggest event of the year, when thousands of runners and spectators descend upon Duluth over several days. Canadian wildfires led to some of the worst air quality the state has seen this week, and people traveling there have likely seen photos on social media where "you can't see the Lift Bridge from across the harbor," Schneider said.

"At the same time, weather patterns change all the time around here," he said.

Air quality in Duluth was rated as "unhealthy" Wednesday, meaning the general public should limit lengthy exertion, and sensitive groups should avoid exercising altogether.

The hazy skies cleared Thursday and air quality is expected to be "moderate" Friday and Saturday with some lingering smoke, according to the Minnesota Pollution Control Agency.

Still, runners should be cautious, said Dr. Chris Delp, who has worked 26 years in the emergency department at St. Luke's hospital in Duluth. The emergency room has seen an increase in patients this week with breathing problems, he said, and is preparing for a potential influx of runners struggling with toxic air, a new situation for the marathon.

With wildfire-induced poor air quality recently in New York, the medical community is learning that tiny particles in smoke can get deep inside lungs, leading to more systemic problems, he said.

"They saw an uptick in heart attacks [in New York] because these particles can kind of set up an inflammatory response," Delp said.

He warns runners to ask for help if they're experiencing lung issues, and for those with asthma to remember inhalers and medications.

While race organizers are optimistic about Saturday's forecast, they have contingency plans for air quality, including more medical personnel along the race route. Canceling the races — which also include a half marathon and a 5K — are a drastic last resort, Schneider said.

Aside from 2020 when Grandma's events were canceled because of the pandemic, since its 1977 inception the race has been delayed but never canceled for weather. Unlike a thunderstorm, air quality wouldn't likely improve quickly enough to simply delay the races, Schneider said.

"It's something that hopefully we don't have to talk about this year," he said.