Why wildfire smoke climbs high into the atmosphere

Wildfire smoke can linger in the atmosphere for days, weeks, and even months, depending on how long a wildfire is burning. When wildfires burn, a lot of smoke is released into the air. These blast clouds can send the smoke from wildfires even higher, reaching more than five miles beyond Earth’s surface in the stratosphere. At any time, changes in the weather patterns can send that hazardous smoke right back to Earth’s surface, impacting air quality thousands of miles from the initial wildfire. [Sources: 7, 8]

With larger wildfires, the smoke can travel several miles up to the stratosphere and travel over an entire region, creating air pollution in areas well beyond where the fires are burning. When forest fires burn over vast areas of land, clouds of smoke, rising as much as 14 miles (22 km) in the air in the stratosphere from strong currents, can travel around the globe. Large fires can send plumes of smoke over entire continents, even oceans. The injection means large fires can dramatically affect the air quality and visibility in cities that are located well outside of smoke origin, which then makes the urban air pollution worse, increasing the risk of health problems and deaths for people who live there. [Sources: 4, 7, 9]

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At night, falling temperatures may result in smoke plumes settling in valleys, deteriorating air quality there. The effect is to decrease the temperature differential between warmer land temperatures and cooler air above. Clouds caused by the fire are produced by the smoke plume because the intensity of the fire’s heat warms the surrounding air, which causes rapid upward movement, drawing cooler air up. [Sources: 1, 5, 12]

The smoke cloud cools down as it rises in the colder upper atmosphere, interacting with particles of ice and building up electrical charges, which may occasionally release lightning. One of the reasons wildfire smoke can create this hanging effect is that the ultra-heated smoke and ash rising in the air can cause Pyrocumulonimbus events, or thunderstorms caused by fires. A blaze that has greater energy will send smoke higher; some fires even produce towering clouds of Pyrocumulonimbus, which can send smoke up to tens of thousands of vertical feet from Earth, and even up to the stratosphere. [Sources: 1, 7, 11]

With more fuel to burn, a fire also may get hotter and more energetic enough that smoke clouds may penetrate natural layers of the atmosphere overhead, provided conditions are right. Wildfire smoke, which is made of mostly dark carbon particles, can block some sunlight from reaching the ground. When smoke is heavy for an extended time, fine particles may accumulate in your home, although you might not see them. Adding the fine suspended particles and gases of the smoke into the burning forest fires produces this grayish-brown mist. Air pollutants travel thousands of miles in the jet stream. The presence of fine particles for thousands of miles indicates that there is a powerful, complicated structure causing it to fail to respond quickly. [Sources: 1, 4, 6]

Fine, inhalable particulate matter (PM2.5) is an air pollutant that is most concerning for public health because fine particles can move deep into the lungs and may also get into your bloodstream. Smoke contains a significant amount of fine particulate matter, known by particle size as PM2.5, that may significantly affect the health of individuals. The implications for public health may be sobering; smoke includes several harmful compounds and fine particles that may make breathing difficult and contribute to illness. [Sources: 0, 1, 5]

Smoke particles may change cloud formation, acting as nuclei for ice particles, potentially impacting weather, while cloud moisture may change smoke’s chemical composition. For instance, recent studies have shown that smoke particles produce clouds with smaller droplets, making them less likely to rain. What is pretty clear at this point, says Cynthia Twohy, an atmospheric scientist, is that the reason why some clouds are as they are is due to the smoke particles — and that this is how they are making it less likely to produce rain. In parts of the Amazon, a complex set of atmospheric physics means smoke dampens clouds at low levels, but it causes storm clouds in the upper atmosphere. [Sources: 2, 5, 12]

Smoke particles, which are injected into the upper layers of the atmosphere, called the stratosphere, can move rapidly across the globe in strong winds, lingering for weeks without rainfall or clouds to draw them away. These gases, smoke, and particles slowly rise from the ground fires, as buoyant forces, exceeded by winds at the surface of the atmosphere, cause those gases to climb farther in the air. Smoke may move further as it increases in density. This smoke has the potential for an explosion caused by a Pyrocumulonimbus, which can happen in certain circumstances. At several thousand feet from the surface of the earth, these explosive clouds may propel the smoke skyward, reaching heights of more than five miles. [Sources: 4, 10]

Smoke from a forest fire may remain in the atmosphere for several weeks while spreading. As trees, brush, grass, and peat are consumed in these fires, massive amounts of smoke, soot, and other pollutants are released into the air. Oil and home burning, for example, produce black smoke, as these hot fires emit large amounts of soot and black carbon. Forest fire smoke, by contrast, tends to be gray, because these lower-temperature fires release lighter-colored organic material and brown carbon (wood and vegetation). [Sources: 3, 9]

Smoke particles may contribute to brighter clouds that reflect sunlight and generally cool the climate. Smoke also changes the temperature profile of the troposphere, which can influence precipitation. [Sources: 2, 10]

As air quality drops, smoke particles may become embedded deep within the lungs, causing a host of possible adverse health effects, says Mark Cochrane, a University of Maryland professor studying wildfires, climate change, and the earth’s systems. Fires in the Amazon, Southern Africa, and Indonesia, for example, send massive plumes of smoke high into the atmosphere, and fine particles do what they do here, just like they do across the Western U.S.: Grow clouds full of tiny droplets, stingy with their trapped water. [Sources: 10, 12]