Smog Alerts Declared in Northern Part of County

First-stage smog alerts were declared in northern Orange County Sunday, the second day in a row that ozone reached unhealthful levels.

On Saturday, first-stage alerts were called in the northern and central areas of the county.

The South Coast Air Quality Management District declared Sunday’s alert at 2 p.m. at its West Lambert Road station in La Habra. Other first-stage alerts had been declared earlier in the east San Fernando and San Gabriel valleys, AQMD spokesmen said.

A first-stage alert, in which air quality is considered unhealthful for everyone, is declared when the ozone level reaches .20 parts per million for one hour, said Jeb Stuart, AQMD executive officer.

Ozone, which is colorless, is often accompanied by minute particles, but not always, Stuart said. This weekend’s weather conditions--summerlike temperatures, a strong inversion and a light wind--are ideal for producing ozone, Stuart said. (A temperature inversion occurs when a layer of warm air prevents the cooler air below it from rising.)

An AQMD spokeswoman said the air quality should improve noticeably in many areas today and that first-stage alerts are predicted only for the San Gabriel and Pomona valleys. The AQMD recommends that schools in those areas cancel outdoor physical activities.