The Twin Cities were less polluted Monday because of dry air moving in.
However, there are days throughout the year, some of which came two weeks ago, that are not so clean.
Soot – which is an air pollutant made of tiny particles – is the main pollutant during the colder months, said Rebecca Helgesen, public information officer with the Minnesota Pollution Control Agency.
Dirty air can cause health problems and eventually tougher pollution controls if the area falls below federal standards for several consecutive years.
From Nov. 12-19, the air quality index, the U.S. Environmental Protection Agency’s measurement for air quality, stayed moderate. That is one step before air is considered unhealthy for sensitive groups.
The Minnesota agency issued air pollution advisories because it was forecast that there would be more pollution in the air, Helgesen said.
When the scale, from the best at zero to the worst at 300, hits 100, it is unhealthy for sensitive groups, and the Minnesota agency issues Air Pollution Alert Days.
The scale peaked at 84 Nov. 18. That is considered moderate, which is “fine for just about everyone,” Helgesen said.
She said the index rises above 100, on average, up to a dozen days per year in the Twin Cities.
Every day, every hour, four pollutants are measured – fine particles, ozone (smog), carbon monoxide and sulfur dioxide. The air quality index number is derived from the pollutant that has the highest number.
Fine particles and ozone are the biggest concern in the Twin Cities, Helgesen said.
She said it is tough to say if fine particles are more prevalent in the area, because testing started here in 2000, when federal law mandated states test it. Numerous other states have “much worse” air quality than in the Twin Cities, so they have used tests longer, she said.
The numbers have been stable for the last four years, though, Helgesen said. Advisories are issued when the air quality index number hits 90 because it can then affect people’s health.
Ozone can cause shortness of breath and eye irritation, she said.
Lori-Anne Williams, communications director for University Services, said fine particles cause lung and heart problems.
Those with respiratory illness or heart disease, along with the elderly and children, are most at risk for problems with pollution, according to the Minnesota agency’s Web site.
She said this summer was cooler than average and the Twin Cities did not have any days when ozone levels went above 100. That is unusual, but it occurred around the United States, she said.
Ozone levels only rise in the warmer months, so the Minnesota agency only monitors ozone levels in the summer. Wind could carry it from other warmer areas though, even when it is cold here, she said.
Minnesota achieves federal standards for clean air – but more because of location than effort to reduce pollution, she said.
Helgesen said she has never seen a day in the Twin Cities with pollution levels unhealthy for everyone.
If the Twin Cities had several years of poor air quality, they could be in violation of federal clean air standards, she said. To lower pollution, methods would include vehicle inspections for proper emissions.
Erin Blower, a University student working on the Clean Air Campaign for the Sierra Club, said she believes the number of days when the air is unhealthy for sensitive groups is increasing. The club is advocating better pollution control, she said.
