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Third day of ozone-heavy air expected across Bay Area

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EPA expects a code orange as East Bay, South Bay heat up

The San Francisco skyline, smothered in unhealthy gray smoke, as seen from Coit Tower.
San Francisco during some of the worst of 2018’s air crisis. Today’s forecast is not nearly this dire.
Via Shutterstock

Update, 8-16-19: For the third day in a row people in Contra Costa and Santa Clara counties will be breathing a little harder on Friday, while less troublesome but still tepid malaise lingers across San Francisco, Oakland, and the North Bay and Peninsula regions.

The EPA’s AIRNow tool again predicts that air quality around cities like Antioch and San Jose will be “unhealthy to select groups” (USG), while “moderate” air stifles the rest of the Bay Area.

Unsurprisingly, the Bay Area Air Quality Management District [BAAQMD] has issued a Spare the Air Alert for Friday. The district notes:

From April to October, warmer temperatures and longer days can cause ozone to build up to unhealthy levels. [...] On Spare the Air Alert days, Bay Area residents should consider limiting outdoor activities. There are everyday behavior changes, such as taking public transit, carpooling, or biking, that can improve air quality year round. These actions are particularly important on days when a Spare the Air Alert is called.

BAAQMD’s own air forecast for Friday predicts similar results as the federal agency’s, with the region’s Eastern Zone—mostly Contra Costa County—rising to 104 and the Santa Clara Valley Zone to around 101 on the 500-point Air Quality Index scale, the very lowest end of the “USG” part of the spectrum.

The EPA notes that “on hot sunny days ozone can reach unhealthy levels” and that “people most at risk from breathing air containing ozone include people with asthma, children, older adults, and people who are active outdoors, especially outdoor workers.”

Exposure to air with excess ozone can make it difficult or even painful to breathe, inflame airways, and “aggravate lung diseases such as asthma, emphysema, and chronic bronchitis.”

Just like the weather, air quality forecasts are a prediction, and the actual AQI may vary throughout the day.

A color-coded map of air quality in the Bay Area, with Contra Costa and Santa Clara Counties colored orange to indicate worsening conditions. BAAQMD

Update, 8.15.19: Wednesday’s air quality forecast turned out to be a little less dire than anticipated, with the Air Quality Index running into the orange in only a few East Bay locales.

Air qualify in San Francisco was worse than anticipated Wednesday, but still only within the “moderate” range of the scale.

However, once again EPA air monitors have predicted much the same for Thursday, with tepid “moderate” air across nearly the entire region and potentially unhealthy USG air—”unhealthy to select groups”—proliferating across the East Bay and South Bay.

Although things could once again prove more mild than anticipated, those who live in affected areas should take reasonable precautions once again.


The Environmental Protection Agency’s (EPA) AIRNow online tool indicates that air quality across the Bay Area is as clean and pristine as ever on Wednesday morning, but according to the forecast that will all change throughout the day, as an unhealthy haze descends on the East Bay and South Bay, accompanied by dangerous triple-digit temperatures.

The EPA site warns that air quality will be “unehealthy to select groups” (USG) across a wide swath of the Bay Area on Wednesday, including cities like Antioch, Livermore, and San Jose.

On the 500-point Air Quality Index (AQI), the USG designation covers the range between 100 and 150, meaning that “although general public is not likely to be affected at this AQI range, people with lung disease, older adults and children are at a greater risk from exposure to ozone, whereas persons with heart and lung disease, older adults and children are at greater risk from the presence of particles in the air.”

Exposure to this degree of pollutants is certainly not good for the general population, but neither does it pose a marked health risk. If possible, those in affected areas may want to minimize time spent outside, doing heavy labor, or with windows open as a precaution.

Air quality will be “moderate” through almost all of the rest of the Bay Area—worse than usual, but still not a problem except “for a very small number of people who are unusually sensitive—but San Francisco is expected to remain clear, as will Oakland and surrounding cities.

In 2018 the Bay Area suffered historically, dramatically terrible air on account of enormous wildfires in other Northern California counties, but right now Cal Fire (unusually) reports only two active burns in the entire state.

As a spokesperson for the Bay Area Air Quality Management District told Curbed SF in 2017, although it’s unusual to see unhealthy air centered on the region it’s also at some points inevitable, as a few bad days and dramatic outliers are simply part of the process, particularly during a heat wave.