Levels of fine particle pollution, also known as PM 2.5, were the lowest in 2003 since nationwide monitoring began in 1999, according to a report just released by the EPA. The improved air quality can be largely attributed to EPA’s Acid Rain Program, along with other programs that reduced emissions that contribute to fine particle formation.

The report, “The Particle Pollution Report: Current Understanding of Air Quality and Emissions through 2003” reviews recent and long-term trends in air quality and emissions, explores the characteristics of particle pollution in the United States, and takes a close look at particle pollution in 2003 (the most recent year for which data are available).

Since 1999, monitored concentrations of PM2.5 have decreased 10% and are now about 30% lower than EPA estimates of levels 25 years ago. Concentrations of PM10 have declined 7% since 1999 and 31% since 1988. Monitored levels of both particles decreased most in areas having the highest concentrations.

Airborne particle pollution is a mixture of solid particles and liquid droplets found in the atmosphere. These particles come in many sizes and shapes and can be made up of hundreds of different chemicals. PM2.5 and PM10 refer to the size of the particles. PM 2.5 (“fine particles”) refers to particles less than or equal to 2.5 micrometers—approximately 1/30th the size of the average human hair. These particles can penetrate into the deeper regions of the body’s respiratory system. Fine particle exposure has been associated with a number of serious health problems, ranging from the aggravation of asthma and the development of chronic bronchitis to heart arrhythmias, heart attacks and even premature death.

While the Agency’s report shows that concentrations of PM have declined, millions of people still live in areas of the country where particle pollution exceed levels established to protect public health. EPA is taking a number of steps to address particle pollution, including the implementation of the Agency’s first fine particle standards, the Clean Air Nonroad Diesel Rule, and finalizing the proposed Clean Air Interstate Rule (CAIR).

Additional information on upcoming attainment and nonattainment designations for the fine particle standard is available on the EPA website.