Wednesday was the smoggiest day so far this year in Ventura County, with pollution levels exceeding state standards throughout the county and prompting health warnings in two areas.
Pollution levels were expected to subside somewhat throughout most of the county today, but were forecast to remain near state thresholds for unhealthful air.
Officials issued a health advisory for 1 to 6 p.m. today for Simi Valley and Moorpark, advising parents and schools there to prevent children from vigorous outdoor exercise. Adults are also cautioned not to exercise outside and the elderly and infirm are warned to stay indoors.
On Wednesday, health advisories were issued in Simi Valley and the Fillmore-Piru area from 3 to 6 p.m., said Kent Field, Air Pollution Control District meteorologist.
"For people who are sensitive to unhealthful air" such as young children, asthmatics or the elderly, Field said, "it's not a good idea to be outdoors or exercising."
The Simi Valley Unified School District was closed in observance of Yom Kippur, and sports practices in Fillmore were nearly finished by the time the school was notified about 3:45 p.m., Fillmore High School Principal Lynn Johnson said. However, two students with asthma were called in from the field immediately, she said.
"I take it seriously and warn those who need to be warned," she said.
Wednesday's smog episode marked the fourth time this year that a health advisory was called and the first time this year that all of the county's six onshore monitoring stations showed ozone pollution above the state health standard.
"It's normal to have higher concentrations in Simi Valley and the lowest concentrations along the coast," Field said. "But today, the pollution is nasty everywhere."
The health advisories trigger a warning system that alerts schools, day-care centers and convalescent hospitals that the air outdoors is unhealthful. People who participate in vigorous outdoor exercise routines are urged to exercise indoors or curb activity until after 6 p.m.
Ozone, an invisible gas, is formed when pollutants mix in sunlight. In Wednesday's case, the higher pollution levels were brought on by temperatures that soared to 91 degrees in Simi Valley, winds that crept into Simi Valley from the San Fernando Valley and a low inversion layer over the entire county that trapped pollutants below.
The state Air Resources Board requires air pollution districts to issue health warnings when the concentration of ozone in the air reaches or is expected to reach 0.15 parts per million or more, the equivalent of 138 on the Pollutant Standard Index. A first-stage alert, which triggers minor cutbacks in activity from industry, is called at 0.20 p.p.m. or 200 on the Pollutant Standard Index.
Simi Valley reached 168 on the index Wednesday, while ozone levels in the coastal areas were measured at 103.
Although Fillmore-Piru reached only 133 on the index, Field said the district issued a warning because officials wanted to "err on the side of caution."
Ozone concentrations in Ventura County air reached 0.15 an average of 18 times a year during the last three years. Ozone in the county has reached the first-stage alert level only twice since 1983.
At 0.15 parts per million, ozone pollution can cause respiratory problems, including painful breathing, coughing, scratchy throat and inflammation of the airways, said Dr. Michael Lipsett, public health medical officer for the state Department of Health Services in Berkeley.
He said ozone primarily affects people doing manual labor, children at active play or athletes--people with respiratory rates high enough that they are taking more ozone into their lungs. Ozone at 0.15 parts per million can decrease ability to breathe deeply for some people, he said.
Ozone has also been indicated as a cause of asthmatic episodes.
The state sets the level at which health problems begin to occur at 0.09 parts per million, while the federal government sets more lenient standards at 0.12 parts per million.
In 1990, Ventura County air exceeded the state standards on 100 days and violated federal health standards on 16 days.
Air Quality Report
This chart shows the ozone levels for Ventura County. Ozone is an invisible irritant that impairs breathing. When it reaches 138 on a federal index, healthy people are advised to reduce physical activity. Pollutant Standard Index 0-50 Good 51-100 Moderate 101-199 Unhealthful 200-299 Very unhealthful 300-500 Hazardous
Today's Area Wednesday forecast Coastal 103 75 Inland Coastal 102 84 Conejo Valley 100 100 Ojai Valley 109 100 Simi Valley 168 138 Fillmore/Piru 133 125 Santa Paula 102 92
Source: Ventura County Air Pollution Control District