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No, The Rain Isn't 'Toxic.' But Here's What to Do When the Smoke Clears

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Bay Area residents will soon breathe a healthy sigh of relief. Rain is forecast to start washing away the region’s toxic air as early as tonight. The National Weather Service predicts rain and southerly gusts for the Bay area through Friday evening.

Air quality experts are not predicting a toxic deluge, as some have suggested on social media.

“Although Paradise experienced a large wildfire, that’s not enough smoke to cause acid rain,” says Dar Mims, meteorologist for the California Air Resources Board. As the winds and rain start to arrive you’re going to wash out the pollution. We will end up with a clean environment after this storm.”

Mims also says the Bay Area’s current haze is much less toxic than in previous days because the most hazardous material from homes and commercial landscapes burnt in the initial days of the Camp fire. The remaining smoke likely emanates from vegetative matter such as smoldering tree trunks, which Mims says is not as bad for human health. He does acknowledge, however, that it’s difficult to assess exactly what kind of particles are carried in wildfire smoke.

“We are all in unchartered territory,” says Mims. “We have never had a smoke event like this. Usually, the rain would have arrived by this time of year.”


Gina Solomon, a physician and air quality expert at UC San Francisco, agrees that residents should not worry about a noxious torrent.

“The first rain will react with the acidic particles and create an acidic and slightly oily mixture on outdoor surfaces, which will be somewhat corrosive and irritating,” says Solomon. “I wouldn’t call the mixture terribly toxic to humans, but it’s best to avoid ingesting it or getting it on your skin until enough rain has fallen to dilute the mixture.” 

Solomon roughly estimates that a half-inch or more of local precipitation would likely be enough water to safely dilute the mixture.

Precautions to Take Once the Rain Arrives

To err on the side of caution, Solomon suggests washing out birdbaths and pet dishes thoroughly. If the rains are lighter than expected, Solomon advises rinsing outdoor furniture with a little soap and water. This is likely not necessary if the storm is a soaker. Either way, it’s probably a good idea to wash cars to prevent potential corrosion.

If you have little ones, Solomon says playgrounds and outdoor play is likely safe, but she does recommend washing children’s hands diligently after any time outside.

Inside the home, Solomon recommends vacuuming carpets, mopping floors,  wiping down hard surfaces with a damp cloth, and then opening the windows to air out the house once it starts raining.  

“Check and replace the filters in your central air system,” recommends Jeff Williams, an air pollution specialist for the California Air Resources Board.

Williams advises wearing respiratory protection like an N95 mask if you’re cleaning an area with a noticeable odor or an area that has visible ash, though he says the risk of toxic exposure is pretty minimal.

Until the first drops arrive, Williams advises residents in the Bay Area continue to stay primarily inside and continue running indoor air filters.

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