WEST LAFAYETTE, Ind. — The Midwest’s summer storms, known for their sudden ferocity and towering clouds, are making headlines for a different reason this year. New research reveals that these storms are propelling wildfire smoke into the stratosphere, a typically undisturbed layer of the atmosphere, with potentially concerning implications for the ozone layer and global climate.
This discovery was made through a study conducted in partnership with NASA, utilizing high-altitude research aircraft to measure the presence of aerosols and burning biomass in the stratosphere. Led by Dan Cziczo, a professor in Purdue University’s Department of Earth, Atmospheric, and Planetary Sciences, the research highlights how these powerful storms are breaching atmospheric boundaries.
Breaking Through the Atmospheric Ceiling
The Midwest, often overshadowed by the Indian subcontinent’s famous monsoon season, experiences its own version of monsoons. These storms, fueled by warm, moist air from the Gulf of Mexico, can become so intense that they break through the troposphere into the stratosphere in formations known as overshooting tops. This phenomenon was observed by Cziczo and his team, who noted that these storms can carry pollutants and aerosols from wildfires into the stratosphere.
“In the summer, particularly in the Midwest, we receive numerous air quality warnings due to wildfires,” Cziczo explained. “We assumed these particles remained close to the surface, but our research aircraft found them in the stratosphere, littering it with biomass particles.”
Implications for the Ozone Layer and Climate
The stratosphere, home to the ozone layer, plays a crucial role in protecting Earth from the sun’s harmful radiation. Typically, only rare events like volcanic eruptions or meteor impacts introduce particles into this layer. However, the study’s findings suggest that human-induced climate changes are impacting the stratosphere’s chemistry and stability.
“This could be a really big deal for a number of reasons,” Cziczo said. “For one thing, for so long, we’ve assumed the stratosphere is a pristine area. But what this shows is that human impacts through a changing climate can affect the chemistry and the radiative ability of the stratosphere.”
These particles can absorb sunlight, warming the stratosphere and potentially affecting its stability, which is vital to maintaining Earth’s climate balance.
The Role of Wildfires
It’s not just the storms that are responsible for these atmospheric breaches. Wildfires themselves can generate storm clouds, known as pyrocumulus, which are capable of launching ash and biomass directly into the stratosphere. Cziczo noted that this was observed during the 2019 Australian bushfires and is becoming more frequent as storm seasons grow warmer and drier.
“There are actually two ways for this stratosphere puncture to happen,” Cziczo explained. “It can be the one severe fire, but it can also be a bunch of little fires that are just constantly perturbing the stratosphere in a way that we didn’t recognize before.”
Exploring the Stratosphere
To study these phenomena, NASA employed a variant of the Lockheed Martin U-2 aircraft, the ER-2, which is capable of reaching altitudes of 70,000 feet. This aircraft, based at NASA’s Armstrong Flight Research Center in California, was temporarily stationed in Kansas to monitor Midwest storms.
“What’s kind of interesting about this, and this is one of these things that I’m not sure that everybody knows about, is that North America has a monsoon,” Cziczo said. “The Midwest has something analogous to that, and it is called the North American monsoon.”
The ER-2’s sophisticated instruments allowed Cziczo and his team to track changes in air quality and chemistry, providing valuable insights into how these storms and fires are affecting the stratosphere.
“Using these very sophisticated tools, we were able to tell that it’s not that we’re just throwing a bunch of tropospheric air and putting it in the stratosphere,” Cziczo said. “Putting this particulate matter in the stratosphere changes the dynamics; it changes the chemistry, and it changes the way that part of the atmosphere works.”
This research, funded by NASA’s Earth Science Project Office, underscores the need for further investigation into the impact of human activities on the stratosphere and its implications for climate change.
As Purdue University continues to lead in scientific research, the findings from this study highlight the importance of understanding atmospheric dynamics in the face of a changing climate. With ongoing efforts to protect the ozone layer, this research serves as a reminder of the delicate balance that sustains life on Earth.
