Cooler, Cleaner Air to Relieve Smoggy Haze, Forecasters Say

The hazy, unhealthful air mass that has hovered over Southern California for the past several days will begin lifting today as a “kinder” low-pressure system moves in from the northwest, bringing cooler and cleaner air, meteorologists said Monday.

The smog alerts in the Southland over the past week were caused by a dome of high-pressure that is expected to begin breaking up today, said Michael Schlesinger, a meteorologist for WeatherData Inc., which provides forecasts for The Times.

A first-stage alert is predicted for today in the eastern San Gabriel Valley, and health advisories are predicted for Pomona, and communities in the western and southern San Gabriel Valley.

But for most of the region, the haziness--which is caused by a mixture of humidity, ozone and particulate matter--will start to disappear. But meteorologists caution that smog will be replaced by cloudy conditions over the region. Daytime temperatures were predicted to drop back into the 70s for most areas, and 60s along the coast for most of the week.

“What’s been happening the last few days is business as usual for this time of year, but a little later than usual,” said Paula Levy, spokeswoman for the South Coast Air Quality Management District.

This year’s smog season was late in arriving, Levy said, noting that the initial first-stage alert this year was recorded June 9 in Glendora. Previously, the latest date for a first-stage alert in the Southland was May 13 in 1983. Last year, the first such event was recorded on May 6.

First-stage episodes are considered “unhealthful” and occur when the Pollutants Standard Index reaches 200. During these alerts, health officials advise against vigorous outdoor exercise and recommend that people with health problems stay indoors.

This year, state air officials have added a new category of alert, called a “health advisory,” which occurs at a PSI level of 138. When this advisory is issued, healthy adults and children are urged to avoid vigorous exercise outdoors. People with health problems also are urged not to exercise outdoors.

The new category, Levy said, was instituted because health studies indicated that lower levels of smog can be harmful.

On Monday, there was a first-stage smog alert in Burbank, and health advisories for Central Los Angeles, West Los Angeles, Pasadena, Azusa, Glendora, Pomona, Newhall, Riverside, Upland, Fontana, Redlands and Reseda.