A Spare the Air alert has been issued for the Bay Area for Wednesday, with "unhealthy" air expected, according to the Bay Area Air District.
The problem is ozone. It was expected to be very hot on Wednesday owing partly to the lack of wind. That will result in high ozone levels, especially in the Santa Clara Valley as well as the Eastern Zone, defined by the air district as including eastern parts of Alameda, Contra Costa and Solano counties.
"When a Spare the Air Alert is issued, outdoor exercise should be undertaken only in the early morning hours when ozone concentrations are lower," the air district said.
Map: California Air Quality Tracker
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Ozone, the air district said, "can cause throat irritation, congestion and chest pain. It can trigger asthma, inflame the lining of the lungs, and worsen bronchitis and emphysema. Long-term exposure can reduce lung function."
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This article originally published at Spare the Air alert issued for Bay Area on Wednesday as intense heat builds up ozone.