Air quality officials issued a health advisory for Moorpark and Simi Valley on Tuesday, warning the elderly and the very young to stay indoors and athletes to reduce strenuous exercise because of ozone pollution.
Air Pollution Control District officials issued the warning after pollution levels in the Simi and Moorpark areas reached 138 on the Pollutant Standard Index on Tuesday afternoon. Anything above 100 on the index is considered unhealthful, and warnings are issued when the index climbs to 138.
The advisory was the third this year. Previous pollution episodes occurred May 9 and Sept. 11.
The unhealthful pollution occurs when a high-pressure ridge combines with high temperatures to heat up the air inland.
That draws pollutants that were blown offshore earlier to the inland valleys, producing ozone. Ozone forms when pollutants from cars and industry mix in sunlight.
But the ridge should move out today, leaving coastal fog, cooler temperatures and better air quality.
Temperatures inland will drop from the low 100s to the 90s or upper 80s and continue cooling into the mid-80s for the weekend. Along the coast, temperatures will drop into the high 60s.