A Spare the Air alert takes effect Wednesday, Sept. 9, across the Bay Area as temperatures in San Mateo could reach 90 degrees and stalled winds trap ozone at ground level.
The Bay Area Air Quality Management District (BAAQMD) issued the alert Tuesday, Sept. 8, citing a forecast of unhealthy air quality driven by high temperatures and light winds. The air district said the Wednesday alert is for ozone and is separate from smoke impacts tied to a prescribed burn on Angel Island that took place Tuesday.
Elevated smog is expected especially in the Eastern Zone and Santa Clara Valley, according to the air district, though the Spare the Air alert applies Bay Area-wide. Temperatures regionwide are running 15 to 20 degrees warmer than normal, according to the Mercury News. Some inland locations could reach 105 degrees.
National Weather Service meteorologist Joe Merchant told the Mercury News that high pressure building over the region is driving the heat wave. "There's no ventilation," Merchant said. "The on-shore flow is basically getting cut off at the coastline if it exists at all."
That stalled sea breeze is also what produces the ozone buildup. The air district said high inland temperatures, combined with light surface winds and a delayed afternoon sea breeze, are expected to elevate smog concentrations.
Ozone health risks
Ozone is different from wildfire smoke.
It can cause throat irritation, congestion and chest pain, according to the air district. It can also trigger asthma, inflame lung tissue and worsen bronchitis and emphysema. Children, older adults and people with respiratory or heart conditions face the highest risk.
The air district advises exercising outdoors only in the early morning hours, when ozone concentrations are lower. Residents should also limit driving, carpool or take transit, refuel vehicles after dusk and avoid idling.
Heat advisory through Thursday
The National Weather Service issued a Heat Advisory running from 10 a.m. Wednesday through 10 p.m. Thursday, Sept. 10. Coastal highs could reach the low 90s, with overnight lows in the mid-60s to mid-70s.
The weather service urged residents to stay out of direct sunlight when possible, stay hydrated and move strenuous outdoor activities to cooler parts of the day. Pets and children should never be left inside parked vehicles, even with the windows down.
The Spare the Air alert covers Wednesday only. No extension had been announced as of the evening of Sept. 8. Residents can sign up for future alerts at SpareTheAir.org.
