Update, 2:25 p.m.: Another "Spare the Air" alert has been issued for tomorrow, July 11, the third this year.
This year's second "Spare the Air" smog alert has been declared for today, Tuesday, by the Bay Area Air Management Quality District.
"Air quality in the Bay Area is forecast to be unhealthy tomorrow, Tuesday, July 10," the district said in a news release Monday.
Dangerous ground-level ozone increases with a rise in temperature in combination with sunlight, oxygen and volatile organic compounds and nitrogen oxides caused by car exhaust, gasoline vapors, industrial emissions and household chemicals, according to the district.
The agency said ozone, or smog, can cause "throat irritation, congestion, chest pain, trigger asthma, inflame the lining of the lungs and worsen bronchitis and emphysema."
"Long-term exposure to ozone can reduce lung function," according to the district. "Ozone pollution is particularly harmful for young children, seniors and those with respiratory and heart conditions."