SAN FRANCISCO (KRON) — On Saturday, the Bay Area Air Quality Management District issued its 21st Spare the Air Alert for smog in 2016, for Sunday, September 18.

Air quality is forecast to be unhealthy again on Sunday. Hot temperatures and light winds will cause air quality to reach unhealthy levels. These conditions combined with motor vehicle exhaust from traffic will cause unhealthy ozone accumulation in the region. Air quality conditions are expected to improve early to mid-week as temperatures drop and winds strengthen.

“The Bay Area can experience heat waves and smog, even as we move into fall,” said Jack Broadbent, executive officer of the Air District. “If we choose to not drive alone, we can reduce air pollution, traffic congestion and protect public health.”

Spare the Air Alerts are issued when ozone pollution is forecast to reach unhealthy levels. Ozone, or smog, can cause throat irritation, congestion and chest pain. It can also trigger asthma, inflame the lining of the lungs and worsen bronchitis and emphysema. Long-term exposure to ozone can reduce lung function. Ozone pollution is particularly harmful for young children, seniors and those with respiratory and heart conditions. When a Spare the Air Alert is issued, outdoor exercise should be done only in the early morning hours when ozone concentrations are lower.

To improve air quality, residents are encouraged to carpool, bike, walk or take transit to work instead of driving alone, not just on Spare the Air days, but every day. The public is encouraged to consider an all-electric vehicle as their next vehicle purchase to help the region reduce the amount of gas powered vehicles that contribute to unhealthy smog. Residents can visit www.stacommutetips.org to find a list of commute programs available where they live and work.

To find out when a Spare the Air Alert is in effect, residents can register for email AirAlerts at www.sparetheair.org, call 1(800) HELP-AIR, download the Spare the Air app or connect with Spare the Air on Facebook or Twitter.

Residents urged to find alternatives to driving alone.

There is no free transit tomorrow and there is no wood burning ban in place.