Clinical and Health Affairs
What's Driving Twin Cities Air Quality?
By Mark Sulzbach
Abstract
Air quality affects the health of patients, particularly those with asthma, COPD, cardiovascular disease, and other heart problems. Epidemiological studies show that common air pollution may have health effects in sensitive populations even when the air quality is within Environmental Protection Agency standards. In Minnesota, the main 2 pollutants of concern are ozone and fine particles. Emissions from motor vehicles are a major source of each. This article discusses these pollutants and reports on the work of the Minnesota Pollution Control Agency in measuring air quality and alerting the public about air-quality problems.
Advances in cleaner fuels and cleaner engines have helped reduce some of the harmful chemical emissions from automobiles. A major improvement to health and the environment occurred when lead was taken out of gasoline in the 1970s. Despite such advances, air pollution is a growing concern in Minnesota. A number of factors account for this. First, the population of Minnesota has grown by 30% in the last 30 years, with most of the growth happening in the Twin Cities metro area. During the same period, the number of cars, trucks, and buses on the road increased nearly 75%. There were 2.6 million cars, trucks, and buses registered in Minnesota in 1975 and 4.7 million in 2000. The Minnesota Department of Transportation estimates a total of 56.4 billion miles were driven in the state in 2004, double the number driven in 1975.1 That’s about 152 million miles per day, which is equivalent to a trip to the sun and halfway back.
In addition, more Minnesotans are driving large, heavy, inefficient vehicles. For the last few years, half of all new vehicles sold in the United States have been in the “light truck” category, which includes sport utility vehicles, minivans, and pickup trucks. In 1980, light trucks accounted for about 20% of new vehicles sold in the United States. By 2004, 50% of all new vehicles were light trucks.2 Despite advances in technology that have improved fuel efficiency in some vehicles, the average mileage per gallon (mpg) for all passenger vehicles has been declining. The fleet fuel efficiency (an average for vehicles within a manufacturer’s classification) of new vehicles actually peaked 19 years ago in 1987. The combined car and light truck fleet efficiency averaged 22.1 mpg that year but only 21.0 mpg in 2005.2
On March 30, 2006, the federal government announced proposed fuel efficiency increases for light trucks. Fuel efficiency requirements will increase from the 2006 level of 21.6 mpg to 22.2 in 2008 and 23.5 in 2010 for vehicles in that category.3 In 2011, the new requirements will for the first time apply to the largest SUVs (those weighing 8,500 to 10,000 pounds).
Vehicle emissions are a primary contributor to air pollution. With the growth of our state’s population and the increase in the number of motor vehicles on the road and the number of miles driven each year, it is not surprising that pollution levels in the metropolitan area remain a health concern.
Minnesota is one of 11 states that meet all federal air-quality health standards. These standards, however, evolve over time and may become more stringent. In addition, standards don’t exist for all pollutants. Still, the Minneapolis-St. Paul area has better air quality than cities such as Denver, which is surrounded by mountains that trap pollutants, or Milwaukee, which frequently inherits neighboring Chicago’s polluted air. Even though the Twin Cities meets federal air-quality standards, it has a significant number of days when the air quality can trigger health problems in sensitive populations.
The Principal Pollutants
Combusting petroleum fuels produce a smorgasbord of toxic pollutants including carbon monoxide, benzene, acrolein, formaldehyde, and 1,3 butadiene. Of these, there is a national health standard for carbon monoxide only, yet all have a deleterious effect on both individual health and the environment. Benzene is a known human carcinogen (it’s been linked to leukemia and other blood-related disorders); formaldehyde and 1,3 butadiene are probable carcinogens. Formaldehyde, 1,3 butadiene, and acrolein irritate the eyes, nose, throat, and lungs. Carbon monoxide reduces oxygen delivery to organs and tissues.4 In Minnesota, the main two pollutants for which there are national standards and which are of widespread health concern in ambient air are ozone and fine particles. Emissions from motor vehicles are a major source for their formation (Table 1).
♦ Ozone
Ozone in the upper atmosphere helps protect us from ultraviolet rays. However, ground-level or tropospheric ozone can trigger respiratory problems such as bronchitis and asthma attacks. Some recent studies even suggest that ozone has a positive association with cardiovascular mortality in the elderly.
Growing Alternatives
Increasing fuel costs and environmental concerns have helped build an impressive market for biofuels. Minnesota produces 2 renewable biofuels: corn-based ethanol and soybean-based biodiesel fuel, both of which pollute less than gasoline and diesel fuel and have obvious economic benefits for farmers.
Not surprisingly, Minnesota is a national leader in producing both biodiesel and ethanol. Ethanol, which also can be made from plants such as switch grass, was first used in 1994 in the Twin Cities to reduce carbon monoxide emissions from cars and trucks and to bring the state into compliance with federal laws.
Ethanol is also the primary fuel in a blend called E85, which is 85% ethanol and 15% gasoline. It is available at 200 gas stations in Minnesota. E85 reduces ozone precursors by 20 percent and can be used on a number of “flexible-fuel” vehicles (mostly, Ford, General Motors, and Chrysler products) that also operate on gasoline. A percentage of federal and state government vehicles are mandated to be alternative-fuel vehicles, which means they can be flex-fuel or hybrid gas-electric vehicles. Nearly half of the Minnesota Pollution Control Agency’s fleet is made up of flex-fuel vehicles, including two gas-electric hybrids.
In 2006, Minnesota became the first state in the nation to require that all diesel fuel sold in the state be a blend of 2% biodiesel and 98% petroleum diesel. Two percent does not have a significant environmental impact, but it’s a start.
Twenty-percent biodiesel blends (B-20) have been used successfully in several government fleets, including some snowplows. Use of B-20 fuels results in slight increases in nitrogen oxides ( 1.2%) but significant reductions in volatile organic compounds (VOCs) (-11%), particulate matter 2.5 microns or smaller (PM2.5)
(-18%), carbon dioxide (-15%), and carbon monoxide (-12%).
Both E85 and B-20 fuels offer significant reductions in PM2.5 and VOCs, which are ozone precursors. Reductions of fine particles and ozone in the air should decrease the chance of health problems among people with COPD, heart, and cardiovascular conditions.
Additional information on the health effects of fuel options is available at the American Lung Association Web site www.cleanairchoice.org/outdoor/. |
The presence of ozone is seasonal. It is produced when heat and sun cook a mixture of volatile organic compounds and nitrogen oxides—both common emissions from internal combustion engines. In Minnesota, this means unhealthy ozone levels are only a threat from April through September.
A study led by Yale University’s Michelle L. Bell published in the April 11, 2006, issue of Environmental Health Perspectives found a strong link between ozone levels and health risks.5 Researchers reviewed air pollution levels in 98 U.S. cities and found increased health risks when ozone levels increased 10 parts per billion, even when cities were within the EPA’s 8-hour ozone standards of 0.08 parts per million (ppm) averaged over an 8-hour period. The authors noted that pollution levels that fall below air-quality regulatory standards should not be misinterpreted as being safe for human health. They concluded that people may be adversely affected by even very low levels of ozone pollution.
A study of health plan claims data led by Michael S. Friedman, M.D., of Johns Hopkins University, showed that reduced vehicle traffic and emissions (a major source of ozone precursors) resulted in lower ozone levels and fewer childhood asthma events.6 During a 17-day period when efforts were made to reduce traffic congestion in downtown Atlanta during the Olympic Games in 1996, ozone levels decreased nearly 28%. During the same period, asthma attacks in children ages 1 to 16 years decreased by more than 40%, and asthma emergencies and hospitalizations decreased 11.1% and 19.1%, respectively.
♦ Fine Particles
Fine particles, microscopic soot, or particulate matter 2.5 microns or smaller (PM2.5) also have a negative effect on health. The major sources of PM2.5 are motor vehicles, electrical power generators, and factories. Particulate matter is a product of combustion processes, but it may also form and change in composition and size as emissions mix in the atmosphere. Unlike ozone, PM2.5 can reach unhealthy levels year round, making it a more persistent health threat.
The cardiovascular and respiratory effects of even short-term spikes in air pollution have been demonstrated in multiple studies. According to the American Heart Association, epidemiological studies conducted around the world have shown “a consistent increased risk for cardiovascular events, including heart and stroke deaths, in relation to short- and long-term exposure to present-day pollution, especially particulate matter.”7
Those studies also described plausible mechanisms linking PM2.5 to cardiovascular disease, including enhanced coagulation/thrombosis, a propensity for arrhythmias, acute arterial vasoconstriction, systemic inflammatory responses, and chronic promotion of atherosclerosis.
A recent study led by Francesca Dominici, Ph.D., of the Bloomberg School of Public Health at Johns Hopkins University, found increases in hospital admissions during PM2.5 events.8 The researchers measured countywide hospital admissions immediately after spikes of PM2.5 and found significant increases in patients with COPD and cardiovascular problems after short-term exposure to PM2.5.
Air Pollution Monitoring in Minnesota
Since 1999, the Minnesota Pollution Control Agency (MPCA) has been measuring and monitoring PM2.5 pollution levels in Minnesota using the Environmental Protection Agency (EPA)-designed Air Quality Index (AQI) (Table 2). The MPCA tracks the level of 5 pollutants—ozone, fine particles, carbon monoxide, sulfur dioxide, and nitrogen oxide—and issues alerts and advisories when these pollutants reach unhealthy levels.
Forecasting ozone or PM2.5 levels is a complex endeavor that involves modeling, air monitoring, weather forecasting, knowledge of topography, experience, and luck. Because air pollution has no boundaries, pollution from the Twin Cities can drift southeast to Rochester or northwest to St. Cloud. Depending on wind and weather patterns, an air-quality event can last from 1 hour up to 4 days. The MPCA currently monitors air quality in 8 locations: Brainerd, Detroit Lakes, Duluth, Ely, Marshall, Rochester, St. Cloud, and the Twin Cities metro area.
In the Twin Cities, the MPCA gathers hourly data from 17 monitors located at 13 stations. The air-quality forecast is listed on the weather page of both daily newspapers. The AQI is updated hourly and is available at the MPCA Web site (http://aqi.pca.state.mn.us/) and on a phone recording (651/297-1630).
The AQI for ozone is calculated from the 8-hour rolling average, and PM2.5 readings are calculated from the 24-hour rolling average. There is often a variance of 10 points among the metro monitors. In rare cases, the ozone reading could spike 20 or 30 points higher at one metro monitor area downwind of the emissions sources.
♦ Air Alerts
The MPCA uses a forecasting service in addition to its own monitoring information and assessment of local and regional weather patterns to determine if an air advisory or air alert will be issued. An e-mail air advisory is sent out if the AQI level reaches 90 or is forecasted to reach or remain at that level. Air alerts are issued when the AQI has or is forecasted to reach 100 or above.
Although an AQI reading may not be high enough to issue an advisory or an alert, people with asthma, COPD, and heart problems can be affected by either ozone, fine particles, or a combination of both when the AQI is in the high end of the moderate range (80 to 100).
Other MPCA Activities
In addition to monitoring air quality, the MPCA is involved in a number of efforts to reduce emissions from motor vehicles and improve air quality.
The MPCA recently worked with Hennepin County and the City of Minneapolis on legislation to reduce hydrocarbons, an ozone precursor. As of January 1, 2006, vapor recovery controls were required at all fuel stations within the 7-county metro area. Now when tanker trucks fill the underground tanks, vapor recovery equipment routes the displaced fuel vapor back into the tanker.
The MPCA also has worked with Clean Air Minnesota, a consortium of environmental groups, government agencies, and businesses, to develop and promote Project Green Fleet. The goal is to install retrofit pollution-control devices on 500 diesel school buses by the end of 2007 to reduce children’s exposure to PM2.5. Research in Atlanta, Chicago, and Ann Arbor, Michigan, has shown that levels of fine particles inside of school buses can be up to 5 times higher than outside of them and can spike up to 10 times higher than levels inside cars traveling the same route.9 The Green Fleet retrofits involve adding a diesel oxidation catalyst muffler and a spiracle crankcase filter, which can reduce PM2.5 emissions by 40 percent. The cost is $2,500 per bus.
In addition, the Minnesota diesel school bus anti-idling law went into effect in July 2003.10 The law requires buses to park and load away from school intake air vents. It is an attempt to minimize idling to reduce children’s exposure to diesel emissions.10
The MPCA also worked with the Metropolitan Council to obtain ultra-low-sulfur diesel fuel at a competitive rate in 2004, when the council began to use it in transit buses. According to the EPA, ultra-low-sulfur diesel fuel, which is federally mandated for use beginning in January 2007, will reduce the amount of sulfur in petroleum diesel from around 300 ppm to 15 ppm. In addition, diesel vehicles manufactured in 2006 and after will have new mandatory pollution-control devices. These 2 measures are expected to reduce harmful pollutants by 95%.11 The EPA claims that ultra-low-sulfur diesel use will reduce nitrogen oxides by 2.6 million tons and particulate matter by 110,000 tons nationwide, which should annually prevent 8,300 premature deaths, 5,500 cases of chronic bronchitis, and 360,000 asthma attacks.11
Summary
Although the Twin Cities has less air pollution than most major cities in the United States, at times air pollution can reach levels that affect the health of certain populations. Individuals’ choices about the cars they drive, how they commute, and how much energy they use directly affect air quality. Physicians should be aware of daily AQI levels and encourage patients, especially those with heart and respiratory problems, to do the same.
Patients who are sensitive to ozone and/or PM2.5 should reduce their level of physical activity on days when the AQI is high to moderate or is considered unhealthy for sensitive groups. For example, patients may need to walk instead of run or postpone exercise entirely until the air quality improves. They also may need to stay indoors, where ozone levels should be somewhat lower.
The AQI and Air Pollution Health Alert are valuable tools that can warn sensitive populations about reducing their exposure to outside air and encourage them to take their medication. Doctors and other health professionals are encouraged to sign up for the e-mail alerts and to recommend that their patients with asthma, COPD, and cardiovascular diseases do the same. To receive the alerts, go to the Minnesota Pollution Control Agency Web site (http://aqi.pca.state.mn.us/). MM
Mark Sulzbach is air quality public information officer for the Minnesota Pollution Control Agency.
References
1. Minnesota Department of Transportation. Transportation Information System Statistics. Available at: http://www.dot.state.mn.us/tda/reports/2004/vmt/fzstvmig.pdf. Accessed April 11, 2006.
2. U. S. Environmental Protection Agency. Light-Duty Automotive Technology and Fuel Economy Trends: 1975 through 2005 - Executive Summary. Available at: http://www.epa.gov/otaq/cert/mpg/fetrends/420s05001.htm. Accessed April 11, 2006.
3. Norman Y. Meneta. Remarks on Corporate Average Fuel Economy (CAFÉ) standards changes. Available at: http://www.dot.gov/affairs/cafe032906.htm. Accessed April 11, 2006,
4. U.S. Environmental Protection Agency, Integrated Risk Information System (IRIS) Database for Risk Assessment. Available at: http://www.epa.gov/iris/. Accessed April 11, 2006.
5. Bell ML, Peng RD, Dominici F. The exposure-response curve for ozone and risk of mortality and the adequacy of current ozone regulations. Environ Health Perspect. 2006;114(4):532-6.
6. Friedman MS, Powell KE, Hutwagner L, Graham LM, Teague WG. 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(7):897-905.
7. American Heart Association, Scientific Statement for Healthcare Professionals From the Expert Panel on Population and Prevention Science of the AHA. Circulation. 2004; 109(21):2655-71.
8. Dominici F, Peng RD, Bell ML, Pham L, McDermott A, Zeger SL, Samet JM. Fine particulate air pollution and hospital admission for cardiovascular and respiratory diseases. JAMA. 2006;295(10):1127-34.
9. Hill LB, Zimmerman NJ, Gooch J. Clean Air Task Force School Bus Particulate Matter Pollution Study. Available at: http://www.catf.us/publications/view/82. Accessed April 11, 2006.
10. Minnesota Statues 2005. School Bus Anti-Idling Law (123B.885 Diesel school buses; operation of engine; parking. Available at: http://www.revisor.leg.state.mn.us/stats/123B/885.html. Accessed April 11, 2006.
11. Environmental Protection Agency Clean Trucks and Buses Rule (2007 Heavy-Duty Highway Final Rule). Available at: http://www.epa.gov/otaq/diesel.htm. Accessed April 11, 2006.