What’s in the air?


Downtown’s overall air quality is no worse than air in the suburbs, but vehicle emissions by commuters have a huge impact on air quality for the entire region.

According to Rick Strassman, supervisor of the air monitoring unit at the Minnesota Pollution Control Agency (MPCA), the air quality Downtown is tracking at levels seen in the entire metropolitan area. Pollutants are well below levels of 15 years ago, he said. The improvements in air quality are attributed to controls on factory emissions, the removal of lead from gasoline and improved pollution equipment on cars and trucks.

“If you live and work in Downtown Minneapolis, the conclusion would be your risk isn’t any greater than many locations around the Twin Cities metropolitan area,” Strassman said, referring to pollutants from vehicle emissions.

He said comparisons between Downtown, the Phillips neighborhood, St. Paul sites and the airport, for example, do not yield statistical differences in pollutants caused by transportation.

Pollution Downtown is dominated by vehicle emissions, and MPCA staff believe there is a morning and afternoon surge in vehicle emissions that disperse fairly quickly.

“Transportation is a big player here, and that’s why we get on the bandwagon for mass transit and reduced driving. It does have an impact on air quality,” Strassman said.

A Hennepin County report notes that ground-level ozone, for example, is not declining, and factors that contribute to ozone formation like traffic congestion are rising.

The U.S. Environmental Protection Agency is expected to impose stricter standards on ozone levels in the coming weeks, and Strassman said the new rules could mean the state would narrowly reach compliance. Ground-level ozone is not concentrated in city centers, Strassman said, but vehicle emissions baked by the sun will produce ozone downwind through a chemical reaction. High levels of ozone in the atmosphere can trigger symptoms of asthma.

The concentration of pollutants from vehicle emissions is within 300 meters of the center line of a major roadway, and past that line pollutants tend to disperse into the “urban soup” typical of a metropolitan area. The particles that make up vehicle emissions are so small they travel through the shell of a car, Strassman said, causing drivers to smell and breathe in the exhaust of other cars and trucks.

Benzene, a byproduct of gasoline that is emitted from car exhaust and tobacco smoke, has been a straggling problem Downtown. It was still tracking at levels higher than the national standard in 2001, but MPCA staff say benzene levels are now within health standards.

Jennifer Tschida, a staff member in the city’s Environmental Management and Safety department, said it is important to note that air quality on top of buildings where monitors are positioned is not necessarily identical to the street-level air quality. A new study taking measurements Downtown at ground level is finding that in certain locations, the amount of benzene can exceed national health standards.

She recommended walking on less-congested roadways, such as Nicollet Mall. That’s especially important for bicyclists who are breathing more heavily and taking in more air, she said.

MPCA studies have found that the state’s greatest potential cancer risks caused by air quality are found in major urban areas such as Minneapolis and St. Paul, as well as small towns with local pollution sources or topography that impact clean air.

More density can lead to more vehicle emissions, but that doesn’t mean Downtowners should pack up and move out to the suburbs, Strassman said.

“We’re all kind of in it together,” he said, explaining that large air masses contribute to overall air quality.

One of Downtown’s prior hot spots for poor air quality is at the intersection of 7th and Hennepin. As part of the Clean Air Act of 1970, the state designed a plan to improve air quality that converted Hennepin Avenue and 1st Avenue North into one-way streets. The conversion was estimated to reduce carbon monoxide by 160 kilograms per day.

The streets will revert back to two-way status in three years as part of the Downtown Ten-Year Transportation Action Plan. A consultant who studied 7th and Hennepin last year said air quality in general has greatly improved since 1979. Consequently, the consultant estimated that carbon monoxide emissions in 2030 would climb to only 50 percent of the national standard if the transportation plan is implemented.

Charleen Zimmer, project manager of the Downtown transportation plan, said she hopes the new strategy will encourage more mass transit use. The plan includes more bike lanes and a conversion to hybrid buses on Nicollet Mall.

“In general, our focus is to do everything we can to encourage greater walking, biking and transit, and there are definitely air quality benefits,” she said.

Although vehicle emissions are the greatest contributor to air pollution Downtown, Strassman noted that gas stations, dry cleaners and body shops are high in toxic emissions.

“How people live affects their exposure, whether indoors or outdoors,” said Tschida.

Reach Michelle Bruch at 436-4372 or mbruch@mnpubs.com.