Bay Area Air Quality warns that the air, made thick by smoke, can irritate your throat, trigger athsma, or worsen many illnesses.
VIDEO: Wildfire smoke turns Bay Area skies dark, murky
"Avoid any outdoor activities, especially if you suffer from a respiratory condition or are a child or elderly person," said Sarah Zahed.
You should also avoid the smoke if you have a heart condition.
All the iconic views of the Bay Area were blotted out by the smoky skies for much of the day. Scientists at UC Berkeley are gathering data on the smoke to learn more about everything from the atmosphere to the agriculture.
Conditions have been clearing up in the East Bay. There is at least some visibility now. You can see your shadow. Earlier Friday it was a total smoke out.
RELATED: East Bay bathed in smoke-driven smog
"We are really worried about the air quality and the effect on our health and our kids," said Davis resident Sharad Jain. "We're trying to stay inside."
It was a quiet day up in the Berkeley Hills.
If you tried, really tried, you could manage to see the outline of San Francisco beyond the campanile.
"Today we are seeing that fires in British Columbia, Oregon, and California are all mixing together and making this lovely soup that we're breathing today," said UC Berkeley Professor of Chemistry Ron Cohen.
RELATED: How to pick a mask for protection during a wildfire
Cohen is doing research on atmospheric chemistry. He says for scientists, the smoke in the air provides a chance to learn more.
"We have a big network that Berkeley manages that makes measurements from San Francisco to San Leandro to Vallejo and we will look at those observations over time," he said.
"We are making measurements in the Sacramento Delta right now and we're looking forward to seeing these measurements and how they affect our data," said UC Berkeley Bio-Meteorology Professor Dennis Baldocchi.
He says smoke reduces the light for the photosynthesis of plants, thus smoke like this could impact California agriculture. But they're also looking at how the smoke could have unintended positive effects.
"Smoke causes light to come in from many many angles compared to a sunny day," Baldocchi said. "When light comes in many angles it can penetrate deeper into the forest."
So, bottom line, the smoke could be altering our ecosystem especially if layers of smoke for days and weeks becomes a normal summer pattern with the increase of fires.
Get the latest weather updates here and recent stories and videos about the California wildfires here.
RELATED WILDFIRE STORIES & VIDEOS:
- MAPS: Wildfires burning across California
- Photos from the wildfires across California
- The latest evacuation orders for Shasta County's Carr Fire, Mendocino County's Complex Fire
- What's in wildfire smoke? Here's how it can impact your health
- VIDEO: Cal Fire says massive fire tornado killed fire inspector in Redding
- Procession held for Utah firefighter killed battling Mendocino Complex Fires
- VIDEO: Vacaville police race to evacuate animals from SPCA as Nelson Fire rages nearbys
- VIDEO: Simulation shows how quickly Carr Fire spread in Shasta County
- San Jose State climate scientists gathering data to forecast wildland fire behavior
- PHOTOS: Massive Carr Fire tears through Shasta County
- How to help Carr Fire victims in Redding and Shasta County, California
- VIDEO: What it's like to fly over the Carr Fire in a Calif. National Guard plane
- VIDEO: Drive through Carr Fire near Redding reveals apocalyptic scenes
- VIDEO: Firefighters get brief rest in neighbor's yard during 'apocalyptic' Carr Fire in Shasta County
- VIDEO: New look at destruction from Carr Fire in Redding
- Most destructive California wildfires in history
- How to prepare for a wildfire evacuation
- PG&E may cut electricity during high fire danger, are you prepared?
- The difference between containing and controlling a wildfire
- These aircraft are on the front lines of the fight against California wildfires
- Wildfire masks: How to best protect yourself from smoke during a fire
- How wildfire smoke can impact your health
- How to sign up for emergency alerts where you live
- Surviving a long-term power outage
- Safety tips to remember when returning home after wildfire
- DIY: How to make a pet carrier in case of emergency
- How to prepare your pets in case of disaster