(Bloomberg) — As fires raged in LA this week, concerned residents have looked to air quality measurements to help determine how safe it is to be outside. Smoke from forest fires can travel thousands of kilometers and affect air quality. making it particularly dangerous for the very young and elderly, as well as those with medical conditions that affect their breathing and circulation.
One way to understand how wildfire smoke causes dangerous air pollution is the Air Quality Index scale, which is often used by weather apps. But that's not the only way to measure it – and relying on that alone can be misleading. Here's what you need to know about air quality, AQI and wildfires.
It is the U.S. Environmental Protection Agency's official way of communicating to the public how safe the air is. It is a scale of numbers and color codes that corresponds to the concentration of five pollutants: ground-level ozone, particulate pollution, carbon monoxide, sulfur dioxide and nitrogen dioxide.
The scale is based on EPA standards for the level of pollution a person can be exposed to over a 24-hour period without harming their health. This scale runs from 'good' to 'dangerous'. The EPA says that readings at or below 100 are satisfactory in the broadest sense. As wildfires rage through Southern California, more than 300 readings have been recorded – meaning the air is dangerous to breathe.
The most dangerous and widespread pollution from a wildfire is particulate matter. These are small soot or dust particles in the air, which can come from everyday pollution sources such as gas cars and stoves, but also from forest fires. PM2.5 are the smallest particles and PM10 are larger.
That's what government websites like AirNow, as well as unofficial apps and monitoring networks, typically measure. They won't necessarily use standard PM2.5, says the California Air Resources Board — so make sure you're looking at the right thing. Short-term effects include irritation of the eyes, throat and lungs, as well as coughing and shortness of breath. In the longer term, it is linked to health problems such as asthma and heart disease.
What's going on with the LA fires and air quality?
Fires can also mean people are exposed to ash particles that are too large to be picked up by air quality monitors, said Scott Epstein, air quality assessment manager at the South Coast Air Quality Management District, which regulates air pollution in the Los Angeles area. The agency provides air quality assessments for the region, but they are only based on five pollutants: ground-level ozone, PM2.5, PM10, carbon monoxide and nitrogen dioxide.
“Our instruments are primarily designed for the pollution you can't see,” he says. “We can't measure ash,” but it is possible to see it with the naked eye, and smelling smoke means ash is probably nearby, he said.
Wildfires in urban areas also release other pollutants, said Anthony Wexler, director of the University of California Davis Air Quality Research Center. “The situation with wildfires is different because there are many other substances in the atmosphere that can be quite toxic.” Modern homes contain metals, plastics and other materials that are released into the air when burned. The most harmful are metals such as copper and chromium, as well as chlorinated compounds such as PVC, which is found in things like plastic pipes.
Unlike particulate matter, there's no good real-time way to test for these pollutants, and you won't find information about them on AQI websites or apps, but “if particulate matter is high in a wildfire smoke situation, everything is high” , says Wexler, “so the gases and all the toxic stuff will be there too.”
Why are some fires worse for air pollution than others?
Wind is a big factor, Epstein says. In the current fires, the same sea breezes that caused the fires to spread so quickly have also blown smoke out to sea, away from many people, reducing the impact on air quality. In 2020, fires near Los Angeles had a much greater effect on the city's air quality as wind direction changed and smoke began blowing onshore.
Even in neighborhoods that are quite close together, conditions can vary depending on the wind direction. In some cases, smoke may be visible high in the atmosphere, but not at ground level, making conditions look worse than they actually are.
“Our worst smoke events that we see are when we have strong offshore winds that start the fires because they are dry and hot, and then we get an onshore switch that merges all the smoke in the region,” Epstein says.
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