Air quality officials say ozone levels are expected to reach unhealthy levels in the Sacramento region this week.
The Sacramento Metropolitan Air Quality Management District says ozone levels will be "unhealthy for sensitive groups" through Saturday. The region typically has higher ozone levels in the warmer summer months.
Christina Ragsdale with the district says anyone can be affected by ozone.
"Often times people have a reaction to ozone and they're not even realizing that's what's going on, they may have some shortness of breath or some little bit of burning in their lungs if they're exerting outdoors," says Ragsdale.
Ragsdale says the most vulnerable are children, the elderly or people with lung illness or heart disease.
She says as the days get shorter, there's less time for ozone to develop in the atmosphere.
Ragsdale says it's possible there could be a "Spare the Air" day Thursday or Friday, when temperatures are forecast to reach 105 degrees or higher.
On those days, people are asked to cut back on driving.