When most people think of unhealthy air, they think of a stifling, summer day, plagued by high ozone levels and a thick layer of smog over the Twin Cities. However, Minnesota’s worst recorded air alert occurred during the winter of 2005, and ozone was not the culprit. Instead, a stagnant air mass trapped fine-particle pollution near the ground.
Ozone still remains a big concern in Minnesota and is capable of triggering respiratory problems such as asthma attacks. It is created when volatile organic compounds (VOCs) from solvents, paints, and combustion emissions mix with other nitrogen oxide emissions in hot sunshine. But because it requires hot sunny weather to produce harmful amounts, it remains only a spring-through-fall problem. Further, it has to start nearly from scratch each day, so harmful levels are rare until late in the afternoon or early evening and are usually short-lived.
Fine particulate pollution is a different cup of tea. It can happen year round. Clouds don’t reduce formation like they would for ozone, but actually help particulate levels build because particulates bind to water. Particulate levels can remain higher much longer than ozone levels. The main sources of particle pollution are coal-burning power plants, factories, vehicle emissions and wood smoke (e.g. backyard recreational fires, wood burning stoves, fireplaces and outdoor wood boilers).
Fine particles are a complex aerosol mixture of liquid and solid airborne particulate matter from incomplete combustion of fossil fuels. Fine particles (smaller than 2.5 microns) are emitted from vehicles, electrical power plants, fires and industry and are so small that 30–100 (or more) could fit across the diameter of a human hair. Once emitted particles are airborne, they can also change their composition by reacting and combining with other particles in the atmosphere.
The Minnesota Pollution Control Agency’s (MPCA) website offers a look at the current pollution levels of the two main pollutants—fine particulates and ozone—with the Air Quality Index (AQI) established by the Environmental Protection Agency (EPA) with a scale from 0 to 500. A reading above 100 reaches the category of Unhealthy for Sensitive Groups—and triggers an air pollution health alert to be sent out by the MPCA. AQI forecasts are also published on the weather page of some daily newspapers.
Over the past fifteen years an increasing number of studies have reported associations between the levels of fine particulate matter (“PM2.5”) in the air and adverse respiratory and cardiovascular effects in people (e.g., increases in daily mortality, illness, hospital admissions and emergency room visits). Scientists have observed these associations even at relatively low ambient levels that are prevalent in parts of the U.S. and Western Europe. Research is currently underway to learn more about the relationship between PM and disease—and to better understand how PM2.5 affects human health. The EPA is expected to lower the thresholds for PM2.5 levels for all the AQI categories, which will trigger more air pollution health alerts in Minnesota.
The health effects of PM2.5 depend on several factors, including the size and composition of the particles, the level and duration of exposure, and age and sensitivity of the exposed person. Symptoms of exposure may include a sore throat, persistent cough, wheezing, shortness of breath, tightness of chest, and chest pain. PM2.5 may also trigger asthma attacks, or even lead to premature death, particularly in the elderly who have preexisting cardiovascular, heart, or respiratory diseases. The smallest particles (1 micron and smaller) appear the most dangerous. They are so small they can pass through the lungs into the bloodstream where they may trigger heart problems in those who have existing heart conditions.
Does the Amount of Traffic Make a Difference?
Though air knows no boundaries, urban air tends to have higher pollution levels than rural areas. Industry, power plants and the emissions from vehicles and lawn and garden equipment are often concentrated in urban areas. Air pollution levels tend to be higher along busy roadways such as urban freeways.
The beneficial health and environmental effects from actually reducing traffic were illustrated in a study lead by Michael S. Friedman, MD (Johns Hopkins): Impact of Changes in Transportation and Commuting Behaviors During the 1996 Summer Olympic Games in Atlanta on Air Quality and Childhood Asthma (JAMA. 2001;285:897-905). The study compared asthma events before and during the Olympics. Results show that by reducing vehicle traffic and emissions (a major source of ozone precursors) during a 17-day period, ozone levels decreased nearly 28% and asthma attacks for children aged 1–16 diminished by more than 40% in two health organizations, and asthma emergency events and hospitalizations decreased 11.1% and 19.1%, respectively. Reduced traffic in Atlanta during the Olympic Games decreased vehicle emissions during the critical morning period. This helped reduce ozone levels and which helped reduce childhood asthma events.
Weather Key To Urban Air Pollution
Wind is the key factor that determines whether air pollution emissions stay in the urban area and build, or blow elsewhere and disperse. Though the Twin Cities creates enough pollution to have levels build to unhealthy levels, if its flat prairie topography is joined by a slight wind it will help disperse and reduce pollution levels quickly. The prevailing wind in the summer is from the south, so it’s not uncommon for northern suburb AQI monitors to show higher readings in late afternoon or early evening as the pollution passes through. In the winter, the wind pattern is reversed and pollutants are often driven south. Winds can also bring pollution from other regions and cities of the country.
Every day we add to particle pollution when we drive, heat our homes, light a wood fire, turn on televisions, lights and computers, mow the lawn or use a snow blower. As energy prices remain high or increase there should be plenty of incentive to reduce energy use, with the added benefit of helping to maintain healthy air quality.
By conserving energy each of us will also be reducing carbon dioxide emissions and helping to reduce global warming. Conserving energy is a win-win-win situation, helping to reduce pollution, fight global warming, and save money.
St. Paul, MN
American Lung Association of Minnesota
St. Paul, MN