SMOG INDEX GETS FINE-TUNED.

Byline: Robert Monroe Staff Writer

Just as Los Angeles comes off its first year without a smog alert, the region's air pollution monitor will unveil a new index today that will redefine how dirty the air is and possibly lead to more frequent forecasts of smoggy days.

The South Coast Air Quality Management District will replace the Pollutant Standards Index with a new Air Quality Index that will take into account the hazards dirty air could pose to those who suffer from asthma and other health problems. The extra distinction is one of several modifications meant to make air pollution forecasts more accurate.

``Even though air quality is steadily improving, people are going to notice days when it is listed as unhealthy,'' AQMD spokesman Sam Atwood said.

The AQMD also is adopting a more stringent measurement of particulate matter in the air that will likely influence smog forecasts. Counts of dust particles smaller than 10 microns in diameter will continue to be measured, but the AQMD will also take counts of particles smaller than 2.5 microns in diameter. A micron is 39 millionths of an inch.

Those smaller particles - products of diesel exhaust, among other sources - are considered more hazardous because they can enter the lungs more easily.

``It's focusing down to the particles that matter,'' said Arthur Winer, an atmospheric chemist at the University of California, Los Angeles, and a former AQMD technical advisory committee member. ``I predict we'll measure only (2.5 microns) sometime down the road.''

The measure of the finer particles will be a factor in the new AQI that could lead to more unhealthful measurements. The new index will also include a new category. The current index reported every day by media outlets, including the Daily News, lists a pollution index reading between 101 and 200 as unhealthful. In the AQI, readings between 101 and 150 will be described as ``unhealthful to sensitive groups,'' a reference to people with respiratory problems.

``The revised index updates air quality information reports for the public to reflect the latest research findings on the health effects of air pollutants,'' said Randy Wittorp, a spokesman for the Environmental Protection Agency. That agency's revisions are the basis of the new AQMD index.

Last year for the first time, greater Los Angeles reached the milestone of no smog alerts, defined by the amount of ozone particles in the air. Atwood would not say how the region would have fared under the new system, declining to provide details of the AQMD's version of the Air Quality Index until a press briefing today.

The new measures adopt an EPA policy that the federal agency itself has not been able to implement because of legal challenges from a trucking association and other groups. Such obstacles do not prevent regional agencies like the AQMD from adopting their own versions of that regulation standard, however.

``The major (urban air quality agencies) like the Bay Area, Sacramento and San Joaquin Valley Unified all have something in the works,'' said Wittorp of the EPA's San Francisco office.

AIR QUALITY INDEX

The South Coast Air Quality Management District is one of several air pollution control agencies adopting a new measurement system defined by the EPA. Changes include the following:

--Adds the air quality category of ``unhealthful for sensitive groups'' and corresponds to index readings between 101 and 150.

--When air quality forecasts fall in this category, agencies like AQMD must state what groups in the population, such as people with asthma, are most at risk.

--The index will include a new measurement specifically of airborne particles 2.5 microns in diameter or less.

--Monitoring agencies must use the color chart below to represent various air quality categories.

Source: Environmental Protection Agency

Bradford Mar/Staff Artist

CAPTION(S):

box

Box: AIR QUALITY INDEX (See text)