Local Smog Still Among Nation’s Worst : Pollution: The atmosphere exceeded federal ozone standards on 33 days last year, more than double the number recorded during 1990.


Ventura County continued to have some of the worst smog in the nation in 1991, according to year-end statistics released Tuesday by the county Air Pollution Control District.

While the air here was better last year than it was on average between 1980 and 1990, the county’s atmosphere exceeded federal ozone standards on 33 days in 1991, more than twice the number in 1990, the statistics show.

Eastern Ventura County and particularly Simi Valley, where surrounding mountains and frequent temperature inversions trap pollution near the ground, traditionally have more polluted air than the western county, said Doug Tubbs, manager of air monitoring and technical services for the district.


Morning sea breezes often blow smog from Ventura County’s coastal cities to Simi Valley, and the wind sometimes carries pollution north into the city from the San Fernando Valley, Tubbs said.

While Ventura County’s air last year met federal and state standards for pollutants such as oxides, nitrogen and hydrocarbons, it often contained too much ozone, a byproduct of those pollutants and the main ingredient of smog, Tubbs said.

Federal standards allow .12 parts of ozone per million parts of air, while state standards allow only .09 parts per million.

Simi Valley’s air violated federal ozone standards on 32 days last year, more than twice the 14 days in 1990 when the city’s air exceeded those standards.

Simi Valley’s air also violated state ozone standards on 97 days in 1991, up from 78 days in 1990.

The Oxnard-El Rio region, often swept by sea breezes, continued to have the best air in the county in 1991, district statistics show. Ozone levels there exceeded state limits on 12 days last year, up from nine in 1990, and never exceeded federal limits.

“When this smog scenario occurs, it’s usually a summertime day,” Tubbs said.

Sunlight converts nitrogen, hydrocarbons and other engine exhaust into ozone, which is trapped near the ground in the county’s inland valleys by warm air masses sitting atop polluted cold air masses, he said.

While ocean air masses keep the Ventura County coast relatively clean of ozone, the valleys produce and trap smog thick enough to put the county among the worst areas in the nation for ozone pollution, according to the district.

Greater Los Angeles has the worst air, followed by Chicago, Houston, Milwaukee and the northeastern U.S. seaboard surrounding New York City. Of the 98 metropolitan areas studied, Ventura County is ranked 10th worst in the nation, district statistics show.

“Obviously, the recipe requires the appropriate topography and weather and emission sources,” Tubbs said.

In Ventura County, he said, “If you move up the coast, you have areas with less population, but similar topography and weather, and they don’t have as severe a problem.”

But while ozone remains a severe problem in Ventura County, the air here was cleaner last year than on average during the previous decade. Ozone levels exceeded the federal standard on 33 days last year countywide, contrasted with an average of 46 days per year during the past 10 years.

District meteorologist Kent Field said, “The persistent low cloud cover that shrouded the coast and much of the county’s inland valleys with fog throughout the summer held temperatures down, reducing the sunshine necessary to produce smog.”

The worst year of the past five was 1988, when countywide ozone levels exceeded federal standards on 54 days and state standards on 125 days.

Smog Levels in Ventura County

Chart shows the number of days that air quality in Ventura County exceeded U.S. and California standards for ozone, the main ingredient in smog. The first figure is the number of days each area exceeded federal health standards during that year. The second figure is the number of days each exceeded more stringent state standards.

1987 1988 1989 1990 1991 Simi Valley 22/79 51/99 40/94 14/78 32/97 Thousand Oaks 02/29 08/39 10/47 03/26 00/20 Oxnard, El Rio 05/29 03/21 02/18 00/09 00/12 Ventura 04/17 01/09 02/13 00/05 02/12 Ojai 03/44 03/51 05/55 02/26 04/30 Piru 05/61 08/39 05/40 03/42 04/44 Countywide 29/114 54/125 44/109 15/93 33/106

Air Quality Report

This chart shows the ozone levels for Ventura County. Ozone is an invisible irritant that impairs breathing. When it reaches 131 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 Tuesday forecast Coastal 33 34 Inland Coastal 36 34 Conejo Valley 26 34 Ojai Valley 28 34 Simi Valley 27 34 Fillmore/Piru na* 34

Source: Ventura County Air Pollution Control District

* Not available