Ozone and heat parts of battling Mendocino fire

SAN FRANCISCO — Firefighters were making progress on extending containment lines on the largest wildfire in Golden State history history, though unhealthy ozone levels caused by smoky conditions and 90-degree temperatures will challenge crews through the weekend, fire officials said Saturday.

The Mendocino Complex, made up of the Ranch Fire and the River Fire, grew slightly overnight on the northern edge and reached 331,770 acres.

It was 77 percent contained by Saturday, according to the California Department of Forestry and Fire Protection, or Cal Fire.

The fires in Northern California have worsened air quality in the Bay Area, prompting officials to declare the eighth Spare the Air alert of the year for today.

Firefighters working on the fire line will face declined air quality because of fine particulate matter in the air, said Kristine Roselius, spokeswoman for the

Bay Area Air Quality Management District.

A high-pressure system over the blaze is creating smoky and hazy conditions for crews on the ground and in the air, said Idamis Del Valle, a meteorologist with the National Weather Service.

Cal Fire officials said heavy smoke is making it impossible for fixed-wing aircraft to navigate, but Del Valle said another weather system is expected to push through this afternoon and last into the week, which she said should clear out much of the smoke and haze.