The thousands of acres burning up northern California created some of the dirtiest air Merced County has seen, San Joaquin Valley Air Pollution Control District officials reported.
Although air quality "improved greatly" on Thursday, officials expect smoke to drift back into Merced County late Thursday or early Friday, said Anthony Presto, outreach and communication representative for the Valley Air District.
The Valley Air District issued an air quality alert until Saturday.
"It is very rare that we see air pollution reach such high levels for particulate matter in the northern region of the San Joaquin Valley as we did yesterday," Presto said in an email to the Sun-Star. "It usually happens very briefly on the evening of the Fourth of July, but that is normally the only time."
On Wednesday, the air reached level 5 in particulate matter, which is considered unhealthy for everyone, according to the Valley Air Districts Real-Time Air Advisory Network, or RAAN. Particulate matter, smoke, dust, ash and soot, can cause "serious health problems, aggravate lung disease, cause asthma attacks and acute bronchitis, and increase risk of respiratory infections," officials said.
Because the winds changed, smoke from the fires in Napa, Sonoma and Solano counties were pushed to the coast on Thursday, Presto said.
Schools in Merced are closely monitoring the air quality and "will take all necessary precautions to protect the health and well-being of our students," said Sara Sandrik, public information officer for Merced City School District.
The Tubbs Fire in Napa County has reached 34, 270 acres as of Thursday afternoon and is 10 percent contained, according to CalFires website. The Patrick Fire, also in Napa County, has burned 10, 817 acres and is 2 percent contained.
The Atlas Fire, in Napa and Sonoma counties, is 3 percent contained and has burned 43, 762 acres. Also in Sonoma County is the Pocket Fire, now at 8, 130 acres with no containment, and the Nuns and Norbbom Fire that's 3 percent contained and has burned 14, 698 acres.
At least 26 people have died and 3,500 homes and businesses have been destroyed by the blazes.
People can go to www.valleyair.org/RAAN to check local air quality conditions.
Monica Velez: 209-385-2486, @monicavelez21