Study Explores the Effect of Smoke on Weather and Climate

A DC-8 flying laboratory developed by NASA was flown recently to initiate an elaborate study into the life cycles of smoke caused by fires in the United States.

This two-month investigation aims to gain a better understanding of the impact of smoke on climate and weather and give information that will result in better air quality forecasting.

A joint campaign—headed by NASA, the National Oceanic and Atmospheric Administration (NOAA), and Fire Influence on Regional to Global Environments and Air Quality (FIREX-AQ)—is targeting extensive questions regarding the physical and chemical characteristics of fire smoke, how it transforms from the moment of combustion to its last fate hundreds or thousands of miles downwind, and how it is quantified. All these factors hold implications for public health.

Ultimately, our goal is to better understand complex smoke-atmosphere interactions to improve the models for air quality forecasts, leading to increased accuracy and earlier notification, which are critical for communities downwind of fires. That common purpose is what brought our agencies together several years ago when we started planning for this major effort.

Barry Lefer, Co-Investigator, FIREX-AQ

Lefer is also a tropospheric composition program manager at NASA Headquarters, Washington.

“We’ve pulled together an outstanding team of scientists who will be using the most sophisticated suite of instruments and models ever assembled to examine the nature of fires and smoke,” stated David Fahey, director of NOAA’s Chemical Sciences Division. “Our long partnership with NASA has taken us literally around the planet and produced too many major scientific discoveries to count. I expect this will be no different.”

The initial phase of the campaign focuses on monitoring smoke arising from wildfires in the western United States. Many aircraft based in Boise, Idaho, are integrated with sophisticated remote sensing and in-situ instruments.

These will operate together to sample the smoke plumes and also their varying chemistry along with weather dynamics, thus monitoring the plumes from combustion to destinations that are usually several states away.

The DC-8 flying laboratory of NASA is a long-distance-traveling scientific workhorse. Two NOAA Twin Otters will be joining in this flying laboratory. In addition, the stratosphere-reaching ER-2 aircraft will be flying out of Armstrong Flight Research Center in Palmdale, California.

The base of operations will shift to Salina, Kansas in mid-August and flights will be directed at smoke arising from agricultural fires in the southeast United States.

Hundreds of these fires occur each year and they are proximally located in population centers; however, their compact size in relation to satellite observational capability means they are not usually detected by the satellites that offer the basis for several estimates of the amounts of smoke emission.

The aircraft observations are equally important for interpreting the dynamics of the small-scale plume and their scientific effects.

Moreover, smoke forecasts are predicated on many different forecast models that utilize satellite inputs and other data, for example, the amount of area which is burned in agricultural fires.

Information like burn scar area, fire intensity, and fuel type, together with temperature, wind, and other weather variables are provided by NOAA and NASA satellites. This information is fed into models that predict the amount of smoke, speed, and direction.

Smoke chemistry begins with the type of fuel, be it a sage brush, oak forests, or pine forests. Apart from gases like carbon monoxide and carbon dioxide, burning will discharge different types and quantities of short-lived gases known as volatile organic compounds, or VOCs.

These compounds mix with sunlight and other types of gases to create ground-level ozone—a harmful gas that damages crops and has an adverse impact on human beings.

Apart from fuel type, the burn’s temperature also has an impact on the ensuing chemistry; on the whole, more carbon monoxide, VOCs, and particulate matter are produced by cooler, smoldering fires but these byproducts are dangerous to human health.

By contrast, hotter, flaming fires create fewer amounts of carbon monoxide, VOCs, and total particulates but it also produces more amounts of black carbon—a type of aerosol material that has additional climate warming potential and is associated with negative health outcomes.

What’s burning matters, but how it’s burning matters maybe even more. Now, with this campaign, we’re taking our understanding from the laboratory to smoke from large fires happening in the field where the atmospheric dynamics change greatly over time and distance. From here, we can continue our work to improve the models.

Carsten Warneke, FIREX-AQ Mission Scientist, NOAA and University of Colorado

In 2016, Warneke and his NOAA colleagues burned different types of fuels at different temperatures in the Missoula Fire Science laboratory. This was done to obtain a more thorough understanding of those factors.

Furthermore, resolving those misgivings in fuel chemistry plays into another area of focus for the joint campaign—that is, plume injection height. That said, plume injection heights rely on an intricate interaction between fire dynamics and the surrounding geography and weather conditions.

More often, cooler fires happen at nighttime and inject smoke low in the air, where it presents a health risk to communities downwind. On the other hand, hotter fires inject smoke into higher altitudes, where it is likely to move farther laterally but more probably stays clear of populated regions.

Considering the significance of their data to forecasting models, many satellites are used for retrieving plume injection heights. While some satellites equipped with LIDAR instruments can be used for direct measurement of injection height, they are not capable of observing the fires more often.

Similarly, infrared instruments integrated on other satellites are used for deriving a measure of the intensity of the fire, and this, in turn, is used to estimate the amount of smoke discharged as well as the injection height, but detection is usually obstructed by clouds and other smoke cover.

The aircraft are directly monitoring plume injection heights and will evaluate them against other direct measurements such as atmospheric conditions, smoke chemistry, and fire radiative power at different altitudes.

This will give a deeper understanding of plume height as a function of chemistry and various other factors, for example, weather.

We’re growing the compendium of observations that can give us confidence that, when we estimate plume rise for the sake of smoke forecasting, we’re going to create a more accurate model that will lead to better air quality forecasts.

Jim Crawford, FIREX-AQ NASA Mission Scientist, NASA Langley

A key focus of the joint campaign is a longer-term enhancement of air quality forecasting. However, FIREX-AQ will also deal with the wider impacts of smoke on climate and weather.

Smoke particles, for instance, can help in initiating clouds. Also, smoke affects the amount of sunlight clouds that is reflected back into the atmosphere. Moreover, the optical characteristics of the smoke particles—the amount of light absorbed and scattered by smoke—relies on their composition and sizes, and also establishes their climate effects.

FIREX-AQ will help in addressing one of the key uncertainties about fire emissions—that is, the materials accountable for the absorption of light in smoke. Conventionally, black carbon is responsible for all light absorption. Joshua Schwarz, a research scientist at NOAA, is aiming to support these aerosol-pertinent aspects of the mission.

Joshua Schwarz, Co-Mission Scientist at FIREX-AQ said, "In recent years, there has been recognition of non-black carbon, light-absorbing aerosol species such as brown carbon. Biomass burning is a major source of brown carbon, and this is a really exciting opportunity in FIREX-AQ because we’ve got the instrumentation necessary to answer the question of fire-smoke brown carbon and how it changes in the atmosphere."

The enhancement that FIREX-AQ brings to interpreting the satellite retrievals of aerosol characteristics over North America will also enhance the value of those observations made over other globe areas.

“If we can improve our understanding of fire emissions in North America, we’ll help take a big step forward on biomass burning’s net global climate impact,” concluded Schwarz.

NASA, NOAA, and university partners are taking to the skies, and the ground, to chase smoke from fires burning across the United States. The Fire Influence on Regional to Global Environments and Air Quality (FIREX-AQ) is starting in Boise, Idaho, with a long-term goal of improving our understanding of how smoke from fires affects air quality across North America. (Video credit: NASA/ Katy Mersmann)