Wildfires are expected to bring unhealthy air to more than 120 million people this weekend, but the smoke and its toxic particles may not always be clearly visible. Some skylines are shrouded in obvious abnormal orange tinges with faint burnt odors. Other horizons may carry no visible indication that something is afoul in the atmosphere — but that doesn’t necessarily mean the air is safe.

Air Quality Monitors

Air quality monitors can accurately track the number of pollutants in our atmosphere. That’s why it’s essential to follow local safety guidance — staying indoors, running air filters and wearing an N95 mask — even if everything looks clear.

When a tree burns, the heat breaks down plant material and releases flammable gases. Some of those gases react with oxygen and become carbon dioxide and water vapor in the air. But if the fire doesn’t have enough oxygen to fully burn the gases, it can produce more thick smoke filled with countless tiny particles and chemicals.

Particulate Matter

The signature yellow, orange and brown-ish color of wildfire smoke comes from a group of pollutants called “brown carbon.” These pollutants tint the sky because they absorb sunlight at shorter wavelengths — responsible for blues and ultraviolet — and allow the longer wavelengths behind reds, yellows and oranges to pass through the atmosphere and reach our eyes.

Brown carbon falls under a class of pollutants known as particulate matter 2.5 (PM 2.5), named because they span about 2.5 micrometers in diameter — about 30 times smaller than the width of a human hair. These fine particles can evade our body’s natural defenses and travel deep inside our lungs, causing breathing or heart issues.

Original reporting: KEYT (Ventura/Santa Barbara) — read the source article.