Should I let my kids play outside in the smog? There's a map for that

By Emily Guerin

Published Jun 22, 2017 5:30 AM

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LOS ANGELES, CA - MARCH 14: Traffic moves along the 110 freeway, after Environmental Protection Agency (EPA) Administrator Stephen L. Johnson this week announced a modest lowering of legal limits on ozone pollution standards, on March 14, 2008 in Los Angeles, California. The change angered not only industry groups who lobbied against the change but also medical, scientific and environmental groups who say that tougher limits are needed. EPA science advisors and a children's health panel had unanimously recommended tougher standards to protect the public, especially children and the elderly, from serious respiratory problems caused by breathing ground-level ozone that aggravates asthma and can lead to premature death, as shown by mounting evidence. A second proposal for more stringent seasonal limits on ozone based on its harm to forests, crops and other plants was reportedly quashed at the 11th hour by President Bush. Governments in areas where the air is declared dirty as the pollution limit of about 84 parts per billion changes to about 75 ppb over an average eight-hour period will have two decades to reduce their emissions. (Photo by David McNew/Getty Images)

Traffic moves along the 110 freeway against a smoggy downtown skyline on March 14, 2008 in Los Angeles, California.

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David McNew/Getty Images

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The South LA region was "moderate" again once the PM 2.5 monitor began working properly. Screenshot taken Wednesday, June 21 at 9:00 am.

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A snapshot of the Air Quality Index from 3:30 pm on Monday, June 20.

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It's called the Air Quality Index, and on bad days, it looks like a stoplight in traffic.

Thirty-eight air quality monitors feed data on ozone, particulate matter and other pollutants into an algorithm that converts the pollution concentrations into a single number, called an AQI value. The scale ranges from zero to an eye-watering 300.

It's rare, but not unprecedented, to see an AQI value above 200, indicated by a purple color on the map. But every day since last Friday, when the heat wave began, the South Coast Air Quality Management District has reported at least one hour of purple every day at either its Crestline or Redlands stations. In a purple area, everybody should stay indoors.

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Red is more common. In these areas, where the AQI values are above 150, pollution is so bad it can affect anyone exercising or spending significant time outside.

In orange regions, pollution concentrations are only bad enough to affect people with respiratory problems. And in yellow areas, all but the most sensitive people should be fine.

Green areas are best, and usually found along the coast or inland after a winter rain -- but the map can be misleading. For example, in the snapshot above, taken at 3:30 p.m. on Monday June 20, South LA appears to be an oasis of pure air in a sea of moderate to severe pollution.

But in reality, the particulate matter sensor at that station was broken. Once it came back online, it began registering concentrations of diesel soot and other small particulates again, bumping South LA back into the yellow zone.

Paige Newman, the Twitter user cited above, lives in Malibu and "literally drives into the smog" when she commutes to Burbank. She likes the map because it's a visual reminder of what she sees every day coming over the Sepulveda Pass.

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Kenny Uong just found out about the map. The high school senior in Glendale said he'd rather get his information from social media and text alerts, and would like to sign up for AQMD's customizable Air Quality alerts. The agency can let you know when air is bad in your neighborhood.