Novel technologies measure ultrafine air pollution in the L.A. basin.

New technologies developed by University of Southern California (USC) engineers to measure the toxic properties of ultrafine particles in air pollution are helping scientists understand the connection between smog and cardio-respiratory disease.

"We are just beginning to realize that these microscopic specks of dust and soot are far more toxic in the human body than larger, coarser particles," said Constantinos Sioutas, co-principal investigator and deputy director of USC's Southern California Particle Center and Supersite.

"They aren't trapped by the nose and trachea, but travel all the way down to the tiniest branches of the lungs and enter the bloodstream through the alveoli, which are very thin-walled sacs of spongy tissue at the ends of the bronchioles," said Sioutas.

Little is known about the chemical composition of this "invisible soot," Sioutas said. Consequently, federal, state, and local air quality management agencies currently regulate particulate matter only in sizes of 2.5 microns and above. Tiny size and the chemical composition of particles are, however, far more important parameters in determining the degree to which they pose a health risk.

Particle smog has been blamed for a 17-percent increase in premature deaths from heart and lung disease, according to recent studies by Harvard University and the National Institutes of Health, among others.

Nationwide, this invisible soot--which is less than 2.5 microns in diameter--has been linked to roughly 60,000 smog-related deaths in the United States each year.

Particulate matter usually contains a combination of fine solids such as dirt, soil dust, pollens, molds, ashes and soot, along with even finer aerosols that are formed in the atmosphere from gaseous-combustion by-products such as volatile organic compounds, sulfur dioxide, and nitrogen oxides, according to Sioutas.

Sioutas' interest in the field began in graduate school at Harvard, where he built his first particle concentrators. He currently holds nine patents on concentrators that can separate the tiniest particles of pollution from the majority of the surrounding gases so that the particles can be studied.

These monitors are able to identify pollutants in discrete size groups: ultrafine particles of less than 0.1 micrometers, such as those generated by combustion; fine particles, ranging in diameter from 0.1 to 2.5 micrometers, such as ammonium sulfate and nitrate compounds, which produce eye-stinging photochemical smog; and coarse, dusty particles larger than 2.5 microns in diameter that contain mostly soil and sea salt elements.

Sioutas has monitored concentrations of toxic particulate matter in the vicinity of interstates 110, 710, and 405, which slices north-south through the Los Angeles basin.

With a team of researchers from USC's department of civil and environmental engineering, and from the school of public health at UCLA, Sioutas made detailed measurements showing that gasoline emissions constituted about 90 percent of all vehicular emissions along the 405 and 110 freeways.

Along Interstate 710, however, 80 percent of the particle pollution came from diesel engines, whose emissions some researchers consider to be more toxic than gasoline emissions.

The findings have raised serious concerns about the adequacy of current national air quality standards for particulate matter. In spring 2003, U.S. EPA was prompted to initiate a new review of particulate matter standards, considering a proposal to impose stricter regulations nationwide on particle mass and chemical composition.