A look into Twin Cities air quality

Although occasional air quality alerts continue to remind Minnesotans that our own outdoor air can be a health risk, the stateâÄôs air quality has actually been improving on most fronts, according to the Minnesota Pollution Control AgencyâÄôs 2009 air quality report to the Legislature âÄî the most recent in a series of biennial reports. The report indicates increasing air quality alerts are due to tightening standards, but air pollutants are still impacting the health of Minnesotans. While the MPCA is working to reduce some types of pollution, other emerging threats must make their way through the research pipeline before they can be regulated.

The Air Quality Index

âÄ¢ Four pollutants âÄî ozone, sulfur dioxide, carbon monoxide and fine particles âÄî figure into MinnesotaâÄôs air quality index, or AQI. The AQI is based on the pollutant with the highest index value, not on a combination of all four pollutants. âÄ¢ The MPCA issues air quality alerts when the AQI is expected to be near or above 100, which indicates that air is âÄúunhealthy for sensitive groups.âÄù In 2008, five days in the Twin Cities reached this mark, and all were because of fine particle pollution. Minnesota air rarely falls into the âÄúunhealthyâÄù or âÄúvery unhealthyâÄù categories. âÄ¢ Fine particles and ozone cause MinnesotaâÄôs air quality alerts today, as better automobile technology and stricter sulfur standards for gas and diesel fuel have decreased carbon monoxide and sulfur dioxide emissions. âÄ¢ Stricter air quality standards have led to more air quality alerts in recent years, even though most pollutants have been decreasing since 1995, the year the MPCA began submitting regular reports to the Legislature.

Air quality is weather-dependent

âÄ¢ Ozone is only measured April through September, because the chemical reaction that creates the pollutant requires heat and light. âÄ¢ Air quality problems are often because of a combination of temperature inversions âÄî where warm air ends up over cold air and prevents pollutants from dispersing âÄî and stagnant air. This contributed to the most recent air quality alert issued in late January. âÄ¢ High humidity helps fine particles form.

Fine Particles

âÄ¢ Fine particles are released directly through combustion and are also formed when certain chemicals combine. âÄ¢ Heart attacks, bronchitis, asthma attacks and other respiratory problems are associated with increased fine particles. The elderly, children and others already vulnerable to cardiovascular problems are most affected by fine particles. âÄ¢ In terms of particlesâÄô health effects, size matters. The focus of particle regulation has been shifting to smaller-sized particles as researchers have found they pose more health risks. In 1997, the regulatory focus shifted from particles smaller than 10 microns (about a sixth the diameter of a human hair) to particles smaller than 2.5 microns, which are now considered fine particles. âÄ¢ In 2006, the Environmental Protection Agency lowered the daily fine particle standard by nearly half its 1997 level but retained its annual standard. Still, some thought the standards should have been lowered further, Lisa Herschberger, MPCA environmental research scientist, said.


âÄ¢ Ozone is formed when chemicals emitted by burning fuels, burning wood and solvents combine and react with the help of heat and light. ItâÄôs most prevalent just outside urban areas. âÄ¢ Inhaling ozone can reduce lung function and aggravate existing conditions like asthma. Ozone can also damage vegetation. âÄ¢ The national ozone standard was reduced by about 6 percent in 2008, and although Minnesota air meets the standard, the pollutant still causes âÄúmoderateâÄù or âÄúunhealthy for sensitive groupâÄù alert days.

Greenhouse gasses

âÄ¢ Minnesota carbon dioxide emissions increased by 50 percent between 1970 and 2006. âÄ¢ Although carbon dioxide isnâÄôt necessarily harmful to breathe, the MPCA is concerned with it and other gasses that cause climate change. Kari Palmer, MPCA environmental research scientist, said climate change is intertwined with air quality. Air pollutants âÄî particulates, in particularâÄî impact climate change, and warming will cause ozone levels to go up, she said. âÄ¢ Currently, there are no state or federal requirements to report greenhouse gasses, but Frank Kohlasch, MPCA air assessment and environmental data manager, said one of MPCAâÄôs top air quality policy priorities is figuring out how to implement a greenhouse gas inventory. âÄ¢ Kohlasch said that waiting for federal greenhouse gas legislation is a major challenge for the MPCA, as it wants to move forward with monitoring plans but doesnâÄôt want to be out of step with federal guidelines when they are created.

Ultrafine particles

âÄ¢ One emerging issue getting a lot of attention from researchers, including some at the University of Minnesota, is ultrafine particles. About 600 ultrafine particles would fit across the width of a human hair. âÄ¢ Ultrafine particles pose special health concerns because their size allows them access to the bloodstream. Still, before these particles can be specially regulated, researchers need to learn more about their health effects, measurement methods and exposure routes. âÄ¢ Mechanical engineering professor David KittelsonâÄôs mobile emissions lab, which directly samples vehicle emissions for particles and gaseous chemicals, allowed University of Rochester environmental medicine assistant professor Alison Elder to look at the effects of real-world highway pollution on rodents. âÄ¢ Environmental health sciences assistant professor Peter Raynor, who has researched ultrafine particle measurement indoors, said part of the trouble is coming up with the right metric for the particles. Environmental Protection Agency particle standards are weight-based, but pound for pound, ultrafines might be more damaging than larger particles, he said. Measuring either particle number or surface area might be more revealing, he added, but those properties can also be tough to measure.