Despite the Clean Air Act passed by the U.S. Congress in 1970, there are still high levels of air pollution in many American cities and counties. The tenth annual State of the Air report by the American Lung Association (ALA) ranks cities and counties for three different pollution categories: small particles, long term pollutions, and ozone. The report looked at pollution levels for 2005 to 2007.

The report defines particle pollution as a "mix of very tiny solid and liquid particles that are in the air we breathe." Particle pollution is categorized by size: coarse, fine, and ultrafine. Coarse particles are between 2.5 and 10 microns in diameter and called PM 10-2.5. Fine particles are 2.5 microns in diameter or smaller and called PM 2.5. Ultrafine particles are smaller than 0.1 micron in diameter, small enough to pass through blood stream.

Some of the key findings:

• One in six Americans lives in an area with unhealthy levels of fine particles pollution.
• Three in 10 Americans live in area with unhealthful levels of short-term particle pollution (92.7 million in 134 counties).
• One in six Americans lives in area with unhealthful levels of year-round particle pollution, over 47 million.

Breathing particle pollution can be dangerous. It can diminish lung function, cause greater use of asthma medication, cardiac arrhythmias, and heart attacks. The latest studies on short term increases in particle pollution listed a number of possible effects:

• Death from respiratory and cardiovascular causes
• Increased infant and young child mortality rate
• Increased numbers of heart attacks, inflammation of lung tissue in young, healthy adults
• Increased hospitalization for cardiovascular disease, asthma, and acute respiratory ailments

Year-round particle pollution can be deadly and shorten life by one to three years, according to studies in the 1990s. The studies also linked increased levels of year-round particles to premature births and serious respiratory disorders.

Unfortunately, year-round particle pollution worsened in 12 cities, including Bakersfield, CA, which took the number one place from Los Angeles.

The report defines ozone pollution as an "extremely reactive gas molecule composed of three oxygen atoms." Ozone is the primary ingredient of smog. Roughly 175.4 million Americans live in counties with unhealthy ozone levels on too many days. In March 2008 the Environmental Protection Agency (EPA) adopted a stricter standard for ozone pollution. Last year the ALA reported only 92.5 million people as living in areas with unhealthy ozone levels. Sixteen of the cities in this year's 25 most polluted cities categories have worse problems with ozone since last year's report.

Breathing ozone may shorten lives. A 2004 study looked at 95 cities across U.S. over 14 years. The study estimated that over 3,700 deaths a year could be attributed to a 10-parts-per-billion increase in ozone levels. Another study published the same week ooked at 23 Europeans cities and found similar effects. In 2005 three research groups (Harvard, John Hopkins and New York University) came to similar conclusions that daily ozone levels and increased deaths linked.

Commenting on the 2005 research, David Bates, MD said, "Ozone is capable of causing inflammation in the lung at lower concentrations than any other gas. Such an effect would be a hazard to anyone with heart failure and pulmonary congestion, and would worsen the function of anyone with advanced lung disease."

A 2008 National Research Council committee reviewed the evidence about the dangers of ozone pollution and concluded that "short-term exposure to ambient ozone is likely to contribute to premature deaths."

Ozone is formed by chemical reactions from two gases, nitrogen oxides (NOx) and hydrocarbons or volatile organic compounds (VOCs) that are emitted from vehicle tailpipes and power plants, among other sources.

California's polluted agricultural valley

Just under one in eight Americans, about 40.5 million in 37 counties, live in areas with unhealthful levels of short-term particles, year-round particles, and ozone pollution. California's San Joaquin Valley, a fertile agricultural area, has high levels of all three. The ALA gave every San Joaquin Valley county failing grade for ozone and particle pollution.

The 240-mile San Joaquin Valley is a big swath of California, stretching 80 miles east of San Francisco in Stockton, to 100 miles northwest of Los Angeles in Bakersfield. The Valley's climate and geography make it a haven for both particle and ozone pollution. It is surrounded by the Coast Range Mountains in the West, and the Sierra Nevada Mountains in the East. The summers are very hot and long, and the winter is foggy.

The Valley is growing faster than any other air basin in California, according to the Union of Concerned Scientists. The increased population means more vehicles on the Valley's roads and highways. As a UCS report stated, "the Valley risks becoming the nation's dirtiest region." The environmental group, Earth Justice issued a similar warning that the Valley is "on track to become the most polluted region in the country."

State regulations will help reduce pollution levels in the Valley. Last October, the state government announced it would enact regulations on diesel powered vehicles, including retrofits for newer diesel trucks, and phasing out older ones by 2012. Diesel trucks emit almost 40 percent of the state's particle pollution, and half of its NOx pollution. In December, the California Air Resources Board (CARB) approved the regulations.

Other related features on Celsias:
Bad Economy, Better Lungs?
What's the Clean Air Act Done for You Lately?

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