The State of the Air in 2004 - 2006

Executive Summary | 2004-2006 | Tables | Methodology | Acknowledgements | Trend Charts

Air pollution continued to challenge the nation in 2004, 2005, and 2006. Some cities—notably Los Angeles and Houston—managed to steadily cut ozone and particle pollution. Progress stalled in many other cities, however, slowing or eroding gains recorded earlier in the decade. For the first time, a city outside of California—Pittsburgh—topped one of the lists of the most polluted cities—and stands on the verge of topping a second. Over 124.7 million people live in places where air pollution levels for ozone or fine particle pollution place human health at risk.

Many cities have multiple problems. Eight metropolitan areas ranked as the nation’s most polluted cities by every measure. Five of the eight are from California—Los Angeles, Bakersfield, Fresno, Visalia-Porterfield, and Hanford-Corcoran—with Washington, DC-Baltimore, St. Louis, and Birmingham rounding out the list. Seven metropolitan areas landed on two of the three lists, including Pittsburgh, Atlanta, New York City, Detroit, Chicago, Louisville, and Merced, California.

Two cities ranked at the top of the cleanest cities in the United States: Fargo, North Dakota, and Salinas, California. These metropolitan areas recorded no unhealthy ozone or particle pollution days and ranked as having some of the lowest annual levels of particle pollution.

Three cities scored the best for ozone and annual levels of particle pollution: Albuquerque, New Mexico; Duluth, Minnesota; and Honolulu, Hawaii.

Policy Changes
On March 12, 2008, the U.S. Environmental Protection Agency (EPA) adopted a tighter national air quality standard for ozone based on the new research that shows serious harm at much lower levels of exposure. Meeting that standard will require redoubled efforts to reduce the nation’s most common air pollutant. The history of battling ozone shows that aggressive measures can cut emissions, leading to much cleaner air. However, the trends shown in this report warn that progress can stall without putting more measures in place to reduce ozone.

Unfortunately, that same day, the EPA announced recommendations for changes that would dismantle the core principles that are embodied in the Clean Air Act. The EPA Administrator offered to allow the state and local governments to determine which pollutants to ignore and which to clean up. The Clean Air Act recognized these pollutants as the national priority because they were the most widespread and dangerous. The EPA has the responsibility to protect the health of all of the public from these pollutants, not just some, and required the states and local governments to reduce the burden of all these pollutants, not just some.

On March 14, 2008, the EPA announced the long-awaited requirements for much cleaner diesel locomotive and marine equipment. Trains and ships contribute tons of diesel particle pollution and tons of nitrogen oxides that lead to ozone problems. This step will help reduce pollution from ports, rivers and industrial areas across the nation. This action will require the clean-up of diesel locomotives, barges, tugs, and boats beginning in 2008.

Particle Pollution
For the first time, a city not in California — Pittsburgh — moved to the top of a most polluted list. Pittsburgh edged out Los Angeles, despite having slightly fewer days in this report than last year. In addition, Pittsburgh’s annual level of particle pollution just missed tying Los Angeles in this year’s report, and may overtake it next year. Aggressive emissions controls in the Los Angeles basin dropped the year-round particle levels by just under one-third during this decade. By contrast, the ranking for Pittsburgh remains only marginally better than in the 2007 report and tied with its level in the 2006 report. Los Angeles remains at the top of the list of cities most polluted year-round by particle pollution.

• Several cities that also reduced year-round particle pollution dropped off the “25 most polluted” list this year, including New York City, Chicago, Philadelphia and Indianapolis. Several cities saw increased particle pollution, including Atlanta, Birmingham, Hanford-Corcoran (California), and Macon (Georgia).

By contrast, most cities curtailed the number of days with dangerous levels of short-term particle pollution. On the list of the cities most polluted by these spikes in particles, cities shifted rankings based more on how they compared with other cities than on their own improvements. Several metro areas had markedly fewer days of high particle pollution, including Washington, DC-Baltimore-Northern Virginia, Eugene (OR), Harrisburg (PA), San Diego and Weirton-Steubenville (WV-OH). Sacramento and Modesto, California reported more days with high particle pollution spikes.

In a report published in January, 2008, the EPA analyzed trends in particlepollution, along with ozone and four other pollutants. The analysis of particle pollution shows a clear drop from 2000 to 2006, but most of that drop occurred between 2000 and 2002. Adjusted for weather, the three-year average particle pollution levels declined during 2004-2006 compared to 2003-2005. However, the adjustment shows a general stalling in particle levels between 2002 and 2006.

Rankings for the year-round particle pollution list also changed despite improved levels in some cities because other cities made even greater improvements. For example, Louisville saw its rankings worsen, moving to 18th most polluted from 22nd, despite a slight improvement in year-round levels because other cities made much greater progress.

A few other cities also improved their air quality, despite continuing to rank in the list of cities most polluted by year-round levels of particle pollution. Detroit and Cleveland both dropped their annual levels. Improvements tapered off in other cities.

Ozone
The five worst cities for ozone all saw good improvement in their ozone levels during 2004-2006, including Los Angeles and Houston—two cities with most infamous smog problems. In particular, Fresno (CA) marked a remarkable decline in high ozone days since a peak in 2001-2003, showing a drop of two-thirds in that metro area’s weighted average. Most cities on the list of the most polluted had fewer high ozone days in the 2004–2006 period, compared to last year’s report, including Dallas, New York City, and Philadelphia. Several cities on the most ozone-polluted list fared worse in 2004–2006 over the previous report—Sacramento, San Diego, Washington, DC-Baltimore, Atlanta and Charlotte. New to the list of most polluted cities for ozone is Birmingham.

Much of the eastern United States continues to benefit from controls placed between 1999 and 2004 on coal-fired power plants and other sources of nitrogen oxides, one of the precursors to ozone. Cleaner cars and other measures continue to cut emissions of volatile organic compounds (VOCs), the other ozone precursor nationwide. The cool, wet summer of 2004 helped keep ozone days down in some parts of the nation, though warmer summers returned in 2005 and 2006.

Although ozone levels remain lower, they appear to be leveling off. In January 2008, the EPA analyzed ozone trends from 1990 to 2006 nationwide and adjusted them for weather, finding that the adjusted levels showed a seven percent decline from 1997 to 2006. However, the adjusted levels between 2004 and 2006 showed a distinct uptick, though still well below the levels of a decade earlier.

Cities showing significantly more ozone problems in the 2004-2006 report include Birmingham, which moved to the most polluted list for ozone for the first time, and San Diego, which returned to the list for the first time since the 2004 report. Many cities on the most polluted list improved, including Merced, California, which improved its ranking to 17th from 6th most polluted. Three cities improved enough to drop completely from the most polluted list, although they continue to receive a failing grade: Milwaukee, Wisconsin; Grand Rapids, Michigan; and Cleveland, Ohio.