SACRAMENTO – The use of oxygen-rich gasoline mandated by the Air Resources Board (ARB) cut wintertime carbon monoxide levels by an additional 10 percent in urban areas across the state this year, contributing to the lowest polluting winter season on record.

A preliminary review of data at 10 monitoring sites from Sacramento and the San Joaquin valleys to the Bay Area and Southern California shows that the carbon monoxide levels, which peak in winter months, actually dropped by about 33 percent below normal. The turbulence from excessively stormy weather conditions was responsible for much of the lowered carbon monoxide concentrations, but an ARB analysis also revealed that the cleaner-burning gasoline was responsible for about one-third of the air quality improvement.

The lower emissions contributed to the first winter with no violations of the carbon monoxide health standard in the Bay Area since modern monitoring methods were introduced and a dramatic decline in the number of health standard violations in studied sites in Southern California.

Jim Boyd, ARB executive officer noted, "The ARB's emission standards for new cars, which are the world's strictest, are the primary means of reducing carbon monoxide, which declines as newer, lower polluting cars replace older, higher polluting models. But this year, the use of oxygenated gasoline was a significant factor in reducing the health risks from carbon monoxide and, in some marginal areas, appears to have made the difference in meeting health standards."

The ARB, which sets clean air specifications for fuel throughout the year, required the use of oxygenated gasoline for the first time this winter. The fuel was sold from November through January in Northern California and will be sold through the end of February in the southern part of the state. The added oxygen, between 1.8 and 2.2 percent by weight (ranging from 6 to 11 percent of each gallon of gasoline), reduces the formation of carbon monoxide in vehicle exhaust by making the fuel burn more completely.

While cities in California joining 23 other urban areas around the country in using oxygenated gasoline, the ARB required less of the oxygen-rich additives, to strike a balance between the need to lower carbon monoxide and to prevent increases in nitrogen oxides, which pose unique wintertime problems in the state.

Just as ozone, more commonly known as urban smog, peaks during the summer months, carbon monoxide is the dominant air quality program in the winter months, with peak concentrations normally found in areas with heavy auto traffic and congestion. The odorless, colorless gas curbs the blood's ability to carry oxygen, posing a particular health risk for persons with heart and respiratory ailments.

 The state's air quality standard for carbon monoxide, 9 parts per million averaged over 8 hours, is intended to protect those people. By comparison, preliminary data on carbon monoxide levels measured this winter at selected sites include:

• In the South Coast Air Basin (Los Angeles area), the number of health standard violations at Lynwood, typically one of the key sites in the basin, dropped from 35 in an average year to 13 this year.
• At Burbank which averages more than ten violations per year, no exceedances have occurred during the period when oxygenated fuel has been required.
• In the Sacramento area, at the El Camino Avenue station normally records about eight violations per year, no violations have been measured.
• At San Jose, in the San Francisco Bay Area, which normally records about four violations per year, no violations have been measured.
• In Modesto, in the San Joaquin Valley, about three violations are recorded each year, no violations have been recorded.
• In Stockton, the Hazelton Avenue site which normally records one violation per year, no violations have been recorded.