Particulate Levels Added to Times’ Daily Smog Report

When Southern Californians think about smog, they usually associate it with a gaseous pollutant called ozone.

But as unhealthful as ozone is, it’s not what we see on a smoggy day. The haze that hangs like a pall over large portions of the four-county South Coast Air Basin is caused by microscopic airborne particles known as PM10 that absorb and scatter light.

Beginning today, The Times will add PM10 forecasts to its daily report on air pollutants found on the weather page. The forecasts are prepared by the South Coast Air Quality Management District.

Forecasts for other air pollutants--ozone, nitrogen dioxide and carbon monoxide--have long been available.

But only recently was equipment developed to forecast PM10 levels. PM10 forecasts can be particularly important to sensitive individuals, such as asthmatics, in planning their activities to minimize exposure, the AQMD said.

PM10 stands for particles of 10 micrometers or less in diameter--about a tenth the diameter of a human hair. In addition to causing haze, they also pose a health threat because they can be inhaled and lodged in the lungs where they can contribute to respiratory problems and even premature deaths among chronic respiratory disease patients if levels are high enough, the AQMD said. Cancer-causing agents and other toxic compounds may also adhere to the particles.

A recent study by the smog agency concluded that $7 billion a year in medical costs could be saved if the region was in compliance with the federal PM10 standard of 150 micrograms per cubic meter averaged over 24 hours. That standard translates to 100 on the pollutant standard index. Any reading over 100 exceeds the standard.

PM10 consists of various compounds, including diesel soot, dust, sulfates and nitrates.

In 1987, average PM10 concentrations in the South Coast Air Basin exceeded the federal standard 80% of the time. Under the AQMD’s new 20-year clean air plan to bring the region into compliance with federal clean air standards, the PM10 standard will not be met until the year 2007.

While other pollutants reach high levels only during certain months of the year, PM10 is a year-round problem in the basin, which includes Los Angeles, Orange, Riverside and San Bernardino counties.