Now the state and local air boards trying to solve the PM 10 problem are wrestling with the very question posed by Riordan and his staff: Should they assign the highest priority to "fugitive dust"--particles of earth from roads, construction sites and fields--or to exhaust from motor vehicles? That debate, in essence, pits Chino's farms against Los Angeles' trucks.
"It's easier for those upwind to ignore this (PM 10) problem, but we can't help but take it more personally here because we are impacted the most," said Younglove, a longtime Riverside County resident. "Politically, it is unquestionably easier to pick on cows--which are phasing out anyway--and rural roads than ships, planes and trains, which are large, important parts of our economy."
About 115 million people in the United States, including one-third of California's population, live in areas where the air violates federal PM 10 health standards set in 1987, according to U.S. Environmental Protection Agency data. The record is far worse for a more stringent state health standard; just one area of California, Lake County, east of Mendocino, complies. However, only the severely polluted areas in California, those that violate the federal standard, face the 1997 deadline for devising a cleanup plan.
In the Los Angeles Basin, violations of the PM 10 health standards occur under an enormous variety of weather conditions, from stagnant summer days to gusty fall winds.
"Really, the only time of year that we are free of higher levels of PM 10 is during the rainy season--most of January, March and the beginning of April," said AQMD senior meteorologist Joe Cassmassi.
As dismal as the record is, research over the past year indicates that the national standard may be too lax to protect public health. In a study of 8,000 people in six cities, the Harvard School of Public Health reported last year that PM 10 increases the risk of early death 26% and shortens lives one to two years in moderately polluted cities--such as Steubenville, Ohio--which already comply with the federal standard. Other research shows that respiratory deaths increase 3.4% and asthma attacks increase 3% for every small increase (10 micrograms) in PM 10.
Still, of all the major air pollutants, particulates remain the most poorly understood.
Even basic assumptions--what is it comprised of and which are the biggest sources--are based on imperfect and outdated databases and models. AQMD measurements that define its composition are almost a decade old.
To resolve some of these uncertainties, the AQMD board recently authorized $600,000 for a 1 1/2-year research project to decipher the chemical makeup of the smallest, most hazardous particles and the role of motor vehicles and ammonia. The agency also is seeking $1.5 million in research funds from other groups, including the city of Los Angeles and the oil, auto, construction and dairy industries.
PM 10 remains such an enigma because it is the only major pollutant that is not identified by its chemical contents. Instead, it is crudely defined purely by its size. An airborne particle of \o7 anything \f7 trapped in a 10-micron filter--mineral, metal, soot, soil or synthetic material--qualifies as the pollutant.
Unlike Palm Springs, which suffers major dust storms, the vast majority of PM 10 in the Los Angeles Basin comes from man-made sources, with only a slight fraction coming from minerals blowing from the land or ocean, said John Watson, a research professor at the University of Nevada-Reno's Desert Research Institute who studies particulates throughout the West.
Each day in the basin, about 850 tons of particulates under 10 microns pollute the air from streets, farms, trucks, buses, cars, oil refineries, mines and other sources, according to an AQMD inventory. Also, about 1,000 tons per day of nitrogen oxides, mostly from motor vehicles, and 200 tons of sulfur from industrial plants can react in the atmosphere to indirectly create particulates.
About one-third of the basin's PM 10 is ammonium nitrate, a blend of nitrogen from vehicles and ammonia released in the air largely from dairy farms.
"It is a very complex pollutant," said White of the lung association. "Not only do you have to worry about direct emissions, but also the secondary sources (from) gases, typically from industrial sources and cars, that get transformed in the atmosphere into particles."
One of the most challenging mysteries is the source and volume of dust that blows from roads and fields. On some nights in Riverside, calcium particles cause dramatic peaks in PM 10, but no one knows where they come from. Watson believes that some type of human activity is stirring up calcium-rich soils.
"The data on fugitive dust are very, very inaccurate and probably overestimated," Watson said. "It's very difficult to trace it back to their sources."