The San Joaquin Valley Air Pollution Control District said the Air Alert for eight counties in the Valley has been extended through today.
High pressure and atmospheric recirculation had prompted district officials to declare a new Air Alert for Sept. 29.
The alert includes the counties of Merced San Joaquin, Stanislaus, Madera, Fresno, Kings, Tulare and portions of Kern.
Air Alerts are called when conditions may lead to ozone formation that results in exceeding health-based ozone standards of 125 parts per billion (ppb) and triggering substantial federal monetary penalties.
This would be the fourth episode of the season and may be the last of the year, as ozone season is ending. Despite a violation of the 1-hour ozone standard this month — which exceeded the limit by just one hour — the past two summers have been the cleanest on record for the air basin for both the 1-hour and the more stringent 8-hour federal ozone standards.