What to know about wildfire smoke and air quality

(Bloomberg) — As fires raged across L.A. this week, worried residents are looking at air quality measures to determine how safe it is to be outside. Smoke from wildfires can travel thousands of miles and affect air quality. This makes it especially dangerous for the young and the elderly, as well as people with medical conditions that affect their breathing and circulation.

One way to understand how wildfire smoke is causing dangerous air pollution is the Air Quality Index scale, which is often used by weather apps. But it’s not the only way to measure it – and relying on it alone can be misleading. Here’s what you need to know about air quality, AQI and wildfires.

This is the US Environmental Protection Agency’s official way of telling how safe the air is for the public. It is a scale of numbers and color-codes that correspond to the concentrations of five pollutants – ground-level ozone, particle pollution, carbon monoxide, sulfur dioxide and nitrogen dioxide.

This scale is based on EPA standards for pollution levels that a person can be exposed to in a 24-hour period without causing any harm to his or her health. The scale ranges from “good” to “dangerous.” The EPA says that broadly, a reading of 100 or below is satisfactory. As wildfires spread across Southern California, readings of more than 300 were recorded – meaning the air is dangerous to breathe.

The most dangerous and widespread pollution caused by wildfires is particulate matter. These are tiny particles of soot or dust in the air, which can come from everyday pollution sources like gas cars and stoves, as well as wildfires. PM2.5 are the smallest particles and PM10 are the larger particles.

This is what government-run websites like AirNow, as well as unofficial apps and monitoring networks, are typically measuring. The California Air Resources Board says they won’t necessarily default to PM2.5 – so check you’re looking at the right thing. Short-term effects include irritation of the eyes, throat and lungs, as well as cough and shortness of breath. In the long term, it is linked to health problems like asthma and heart disease.

What’s going on with LA’s fires and air quality?

Scott Epstein, air quality assessment manager for the South Coast Air Quality Management District, which controls air pollution in the Los Angeles area, says the fires could also mean people are being exposed to ash particles that air quality monitors can detect. Too big to be picked up by. The agency provides air quality ratings for the region, but it is based on only five pollutants – ground-level ozone, PM2.5, PM10, carbon monoxide and nitrogen dioxide.

”Our instruments are essentially designed for pollution you can’t see,” he says. ”We can’t measure ash,” he says, ”but it’s possible to see with the naked eye, and the smoke. Smelling ash means that ash is probably close.

Wildfires in urban areas also emit other pollutants, says Anthony Wexler, director of the Center for Air Quality Research at the University of California Davis. “The situation with a wildfire is different because there are a lot of other things in the environment that can be quite toxic.” Modern homes contain metals, plastics, and other materials that expand into the air when they burn. The most harmful are metals like copper and chromium, as well as chlorinated compounds like PVC, which are found in things like plastic pipes.

Unlike particles, there is 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 particles are high in wildfire smoke conditions, everything is high.” Is,” says. Wexler, “So the gases and all the toxic things will be there too.”

Why are some fires worse than others for air pollution?

Wind is a big factor, says Epstein. In the current fire, the same offshore winds that caused the fire to spread so rapidly have also blown the smoke out to sea away from many people, reducing the impact on air quality. In 2020, wildfires near Los Angeles had a severe impact on the city’s air quality, as wind direction changed and smoke began billowing ashore.

Depending on wind direction, conditions can vary even in neighborhoods that are fairly close to each other. In some cases, smoke may be visible high in the atmosphere, but not at ground level, making conditions appear worse than they actually are.

Epstein says, “Our worst smoke events that we see are when we have strong offshore winds that fan the fires because they’re dry and hot, and then we get an onshore switch that stops the area. “Collects all the smoke.”

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