Special Report

America's Most Polluted Cities

There’s no doubt that great strides have been made in air pollution. Awareness, stricter legislation and improved technology have all contributed to improved air, land and water conditions. In fact, the nation’s air quality is much cleaner than it was in some of the worst-affected areas, according to a recent report by the American Lung Association. Air emissions that contribute to pollutants have fallen since 1970 thanks to the Clean Air Act.

Despite the improvements, 4 in 10 Americans live where pollution levels are often dangerous to breath. Since the ALA began studying particle pollution, almost all of the most polluted cities have consistently remained among the worst. Pittsburgh has been one of the 10 most polluted cities since 2004. The cities of Bakersfield and Merced, in California, are the most polluted cities in the U.S. this year and have been among the 25 most polluted since at least 2004. They are among many California cities, including Los Angeles, that have struggled with pollution for some time.

The ALA’s 2013 “State of the Air” report measures cities based on low-lying ozone pollution, as well as both short- and long-term particle pollution. These particles, just 1/30th the diameter of a human hair, are capable of getting past our bodily defenses and cause physical harm, particularly to those who already suffer from pulmonary diseases, the very young and the elderly. The report measures both the total accumulated particle pollution over the course of a year, as well as the number of days that the air pollution hit unhealthily high levels. Based on the average levels of long-term pollution measured by the report between 2009 and 2011, these are the most polluted cities in the country.

Eight of the 10 most polluted cities are located in California and are either on the coast or in the San Joaquin Valley. Conditions that make pollution in the valley worse are extremely heavy traffic, which accounts for as much at 89% of all pollution in the valley, and high levels of agriculture in the area.

Janice Nolen, the ALA’s assistant vice president for national policy, noted that the San Joaquin valley has had major agricultural growth in recent years. Agriculture creates pollution in a variety of ways, from the actual tending of the crops to the vehicles that bring supplies in and food out. A review of Census data shows that agriculture, fishing and forestry represent more than 10% of the economy in many of the highly polluted metro areas, compared to just the roughly 2% of all jobs nationwide.

The Los Angeles port is also a major source of pollution, with the diesel exhaust from the oceangoing ships generating significant particle pollution.While part of the high pollution levels in these cities comes from local sources, Nolen noted that much of it also comes from being downwind from cities that are even larger producers of pollution.

In the case of the California cities, it is their proximity to Los Angeles. “California has historically had the biggest challenge in its cities. Part of that is the sources, and part of it is the geography — pollution that might blow somewhere else gets captured in the valleys.”

A review of the pollution levels in these California cities shows that while they remain among the worst in the country for both particle and ozone pollution, they have been improving markedly in recent years. Los Angeles, for example, has reduced its number of unhealthy particle pollution days by more than 50% since 2000.

This improvement reflects the state’s efforts to deal with the problem, Nolen explained. “California has really been, in many ways, leading the nation, because they recognized they had the worst problems.” When the Clean Air Act was signed into law in 1970 the state was given additional resources and authority to be “more aggressive,” said Nolan.

One of the problems the state has focused on is car emissions. “Cars in California have been required to be much cleaner, and some of those standards have been adopted in other parts of the country,” she said. The state is also trying to cut down on other sources of pollution like wood burning.

The only two metro areas on this list that aren’t located in California are Cincinnati and Pittsburgh. Much of the pollution problems in these areas are due to substantial industrial presence. Nolen mentioned that much of the pollution in Pittsburgh is due to the U.S. Steel Plant. The coal industry’s presence in Cincinnati is also a major factor in pollution as big companies such as Duke Energy operate plants in the region.

Based on average long-term particle pollution figures collected by the ALA between 2009 and 2011, 24/7 Wall St. identified the 10 most polluted cities in the country. Merced’s year-round particle pollution ranked as the worst in the nation, in a tie with the Bakersfield-Delano metro area. We also reviewed ozone pollution and short-term particle pollution, which the ALA measured as the number of days between 2009 and 2011 where pollution levels were deemed unhealthy. For each of these metropolitan areas, the ALA noted the population and the number of people in the area with health problems that high pollution can exacerbate, such as asthma and cardiovascular disease.

These are America’s most polluted cities.