Science of Smoke Illustrated

Narration: Kirk Knobelspiesse

Transcript:

Smoke is not a monolithic thing. Smoke is a mixture of gases, liquids, and primarily particles, which are also known as aerosols. PACE is gathering data on these aerosols so that we can get a better picture of how smoke interacts with the atmosphere, and all kinds of far-reaching effects.

What a fire emits is highly variable, and it can depend on the number of factors such as fuel, moisture, and the efficiency of the combustion.

An efficiently burning fire can have dark colored smoke, releasing a lot of carbon monoxide and carbon dioxide.

A less efficient burning fire can have different colored smoke, a lighter colored smoke, and in addition to the carbon monoxide and carbon dioxide, also releases a number of other chemical compounds into the atmosphere.

Soot or black carbon, is a result of efficient burning, and soot consists of chains of elemental carbon, sort of like graphite.

Because they’re dark, soot particles absorb energy from the sun and warm up the air surrounding the particle.

Emitted alongside black carbon are volatile organic compounds. These are gases which can condense downwind from a fire onto the soot.

These created particles are called secondary organic aerosols, which means that there are not emitted at the source. Secondary organic aerosols also form when smoke interacts with the atmosphere.

So one way in which secondary organic aerosols are formed is through photochemical reactions. That means sunlight interacts with gases emitted from smoke, and those gases condense to form either particles in their own right or form onto existing particles such as the soot which was emitted originally.

Another type of aerosol from fires is called brown carbon, and in this case the smoke is, as one could expect, brownish in color, meaning it's absorbing more light towards the blue and ultraviolet portion of the electromagnetic spectrum.

Brown carbon is formed when vegetation burns, and incorporated into the smoke are what are called humic substances, and these are the remnants of vegetation material. Imagine the pigments that are in leaves as they decompose.

All of these different smoke components have different optical properties, and these optical properties describe how those particles interact with light.

The instruments on PACE can measure some of those properties, including at different wavelengths of light, at different geometries and angles.

And from that data, we can figure out the quantity, the color, the composition, the shape and the size of aerosols in the atmosphere, including smoke aerosols.

We use all of that information together, and we use that to differentiate between smoke and other types of particles in the atmosphere, such as dust or different types of smoke from each other.

The data from PACE will help inform wildfire models, but also give us a general better sense of how aerosols from smoke impact things like air quality, human health, weather, cloud formation and other aspects of how our planet Earth works.