COUNTYWIDE : Breezes From Baja Bring Clearer Air

A weather system moving north from Baja California helped improve air quality in Ventura County on Thursday, and pollution is expected to stay in check today, officials said.

Air pollution in Simi Valley was expected to remain unhealthful by state and federal standards today, but it was forecast to stay well below 132 on the Pollutant Standard Index, the point at which the first health warnings are issued.

A health warning was issued for Simi Valley and Fillmore/Piru on Wednesday, the smoggiest day in Ventura County this year, and another warning was issued for Thursday afternoon in Simi Valley and Moorpark.

But pollution levels on Thursday, which remained at 119 in Simi Valley and 97 in Piru, did not reach the point at which it is assumed that air contaminants can damage lungs of young children, the elderly and healthy people engaged in vigorous exercise.

Air quality in the rest of the county was in the moderate level on Thursday and was predicted to remain moderate today.

Wednesday’s pollution episode occurred when a high pressure system, essentially a band of warm air in the atmosphere, trapped the pollutants below. Warm temperatures allowed the contaminants to cook into ozone, a colorless gas that can harm lungs and inhibit breathing. In addition to contaminants produced in Ventura County, winds were drawing more pollution from Los Angeles.

But Thursday, a cooler weather system blew north from Baja and weakened the high pressure system, allowing the pollutants to disperse into the atmosphere.