Particulate matter (PM) describes a mixture of tiny solid particles such as dirt, soil, dust, and ashes, as well as liquid droplets that are suspended in the atmosphere. Some particles are large or dark enough to be seen as soot or smoke. Others are so small they can be detected only with powerful microscopes. Particulate matter can come from factory and utility smokestacks, vehicle exhaust, wood burning, construction activity, agriculture, and natural sources such as volcanoes.

Devices to control the release of airborne particles were among the first pollution control technologies developed for utility power plants. All coal-fired electric utility boilers built or modified after August 17, 1971, are required to limit particulate emissions. Boilers built or modified after September 18, 1978, must comply with an even more stringent particulate emission limit, effectively requiring a reduction of emissions by at least 99 percent. Airborne particles are also regulated as "criteria pollutants" under EPA's National Ambient Air Quality Standards program, so emissions from coal power plants can also be limited by State Implementation Plans.

	IF DOE IS SUCCESSFUL...
	The estimated market penetration for advanced particulate control technologies is 253,000 megawatts under current regulations. If DOE can help produce more effective particulate control technologies, U.S. ratepayers could save $150 million per year by 2010.

To date, most particulate control technologies have been installed to prevent so-called "coarse" particulates from escaping into the atmosphere. Coarse particulates are those with diameters of 10 microns or less (a micron, or micrometer, is 1/25th of a thousandth of an inch); thus, they are referred to as PM10. Power plants typically install either baghouses (essentially large fabric filters) or electrostatic precipitators (devices that use electrical charges to attract particles) to capture solid particles emitted from their coal furnaces.

Today's challenge in particulate control largely focuses on much smaller particles - those with diameters of 2.5 microns or less, or as they are called, PM2.5. PM2.5 particles can be as small as 1/30th the width of a human hair, or smaller. These fine particles are of special health concern, since they can be more easily inhaled deeply into the lungs where they can be absorbed into the bloodstream or remain embedded for long periods of time.

In July 1997, the Environmental Protection Agency set a new stricter standard that will regulate PM2.5 for the first time. The new standard is to be phased in over a decade.

The technical challenges confronting coal-fired power plants in controlling PM2.5 are two-fold: Utilities must develop better ways to reduce the solid fly ash (soot) particles that are produced when coal is burned. And they will likely be required to make further reductions in emissions of sulfur oxides (SOx) and nitrogen oxides (NOx). The reason is that these stack gases react in the atmosphere to form aerosol particles, i.e., sulfate and nitrate salts. There aerosols are referred to as "secondary" fine particulates, and they can add to overall PM2.5 levels in the atmosphere.

DOE's Research Role

The Energy Department's Office of Fossil Energy has focused on two major areas of PM2.5 research: (1) to characterize and understand PM2.5 particles in the atmosphere and use the information as chemical "fingerprints" to identify the sources of the particles and the most effective control strategies, and (2) to develop improved control technologies that can reduce emissions of both solid particles and SOx and NOx precursor gases.

The goal of the air quality monitoring efforts is to produce a comprehensive, high-quality database characterizing PM2.5 emissions from utility plants firing high sulfur coals. In February 2002, Advanced Technology Systems, Inc., of Pittsburgh, PA, won an Energy Department competition to develop the computer based system. Ambient air quality data collected from several ongoing projects in West Virginia, Pennsylvania, and Ohio will be entered into a common database. A publicly-available, user-friendly, web-based tool then will be created to access, display, analyze and interpret the data. In FY 2003 a contract was awarded to the Electric Power Research Institute to cooperate with DOE's National Energy Technology Laboratory to perform an in-depth ambient air quality analysis in a region where high sulfur coal is used in power plants. These results will augment the PM2.5 database.

The complete database for full public access is nearing completion, but an early prototype of the web tool is available to environmental professionals now.

To improve the capabilities of power plants to capture primary particulates, the Energy Department's Fossil Energy program assisted in the development of devices that combine the best features of both a baghouse and an electrostatic precipitator (ESP) in the same compact enclosure. This device removes at least 99.99% of the solid particles in the flue gas of coal-fired power plants. Other projects developed improvements to the efficiency of existing electrostatic precipitators by installing a device that concentrates particles escaping the ESP and recycling them back to the ESP inlet. Another project developed low-cost, non-toxic conditioning agents that are injected in flue gases before they enter the ESP to make the tiny particles more susceptible to capture.