Science in the Sky

A Life of Science: A Series by New Scientists

Airplanes help us collect previously unattainable data by, for example, harvesting water from clouds or tracking wildfires while they’re burning.

  

I opened the door to the airplane hangar and couldn’t believe the size of the plane in front of me. To the average person, an airplane is just a transportation vehicle, used for moving humans and cargo over long distances. For a long time that was how I saw them too, chartering me from Arizona to Indiana, my parents’ home state, every couple of years. I never understood how people could distinguish different types of planes flying overhead just from their general shape or the sound they made. That was how I saw them—until I found myself face-to-face with an aircraft that reminded me of Frankenstein’s monster.

The airplane in the hangar had a dominating presence, even though it was smaller than an average commercial airliner. Part of that commanding presence came from the chill of the hangar itself. I shivered as I took my first step up the short airstair of the NASA HU-25C Guardian Falcon. I had never been on a non-commercial aircraft before, and this plane was quite different from the one I had taken from Tucson, Arizona to Hampton, Virginia just two days prior. It looked normal enough on the outside: shiny, white paint; small, rounded windows; two wings. My first look into the plane’s interior was a spooky sight, however: instead of seats, it seemed as if a whole science laboratory had been crammed into a space the size of a hallway. While it was strange, there was also something inspiring about this little flying lab, knowing how integral it was to my Ph.D. research at the University of Arizona.

My research team uses data and samples collected on airplanes to understand the complex relationships between aerosol particles, clouds, meteorology, and the environment, such as the way a cold front could change the lifespan of aerosol particles in the atmosphere. Airplanes help us collect previously unattainable data by, for example, harvesting water from clouds or tracking wildfires while they’re burning.

One aspect of my work is centered on the California fires that occurred during the summer of 2020. It was the largest wildfire season in modern history for the state, with around 10,000 fires burning over 4.2 million acres, or more than four percent of its land area. There were several factors leading to and aggravating these fires, including intense thunderstorms, a record-breaking heat wave, and the strong, dry Diablo and Santa Ana winds.

Fires are important to track and monitor for many reasons, including air quality. The Clean Air Act requires the Environmental Protection Agency to set National Ambient Air Quality Standards for six common pollutants. Two important pollutants are PM₁₀ and PM_2.5, or particulate matter that is 1/7th and 1/28th the size of a stand of hair, respectively. These aerosol particles—like dust, smoke, and sea salt—are small enough that they can be breathed in, go deep into your lungs, get into your bloodstream, and cause serious health problems. A common source for these particles is wildfires, and these supermicron particles, which are greater than 1 micron in diameter, have been shown to travel hundreds of miles from their origin point. The health impacts and the fact that these particles can traverse the entire United States mean it is important to study these particles whenever we get the chance.

In addition to air quality, supermicron particles affect our atmosphere. The particles that are generated from smoke and fires are dark, like soot and ash, and can warm the surrounding atmosphere and evaporate cloud droplets. When cloud droplets evaporate, it decreases the water content of the cloud and its reflectance, causing more radiation to reach the Earth’s surface and even more planetary warming. It is important for our health and the planet’s health to learn all we can about these fires and the particles they produce.

I use models to trace and project the movement of air masses during a given time period and can determine, for example, if the smoke from California reached almost 3,000 miles to the East Coast. I can track where these smoke plumes moved and use different monitoring stations across the country that collect aerosol samples to understand how these particles changed over their lifetime.

While I may not be helping track down a thief, I am helping to better understand how large particles impact our environment and climate change, which is still one of the biggest unsolved cases.

My job as a researcher is like being a detective. I have evidence (or, in my case, data) in front of me, but when it’s all jumbled together, the story doesn’t make a lot of sense. I have to put together the important pieces of information and start making connections. I analyze data on gases and particle types that I know come from fires to determine the atmospheric composition of a sample site. Based on witness statements, I can put a timeline together; using models and equations, I can predict the forward and backward movement of aerosol particles. By the end of the investigation, I have the culprit, timeline, and, possibly, the motive.

At the end of my project, for instance, I could pinpoint a couple of fires that acted as a source of aerosol particles. Then, I could determine that the particles were transported from California to the East Coast, and they actually gained mass during that journey and became more spherical. As a sort of conclusion, I could find that there was a corresponding increase in cloud cover when the aerosol particles were transported out of California. While I may not be helping track down a thief, I am helping to better understand how large particles impact our environment and climate change, which is still one of the biggest unsolved cases.

As I walked onto the research plane, I rubbed my eyes almost comically, shocked at what I was seeing: on either side of the narrow aisle, almost every square inch of the interior was filled with various aerosol sampling instruments. Where commercial planes would have seats, this plane had rack after metal rack containing expertly jigsawed sampling and analyzing instrumentation. There were dozens of tubes running along the ceiling and walls, from the cockpit all the way to the tail, transporting air from outside the plane to every piece of equipment. There was barely enough room for the two flight scientists to sit at their workstations—just a monitor and a keyboard—and prepare for the four-hour flight.
 

 
In order to sample aerosol particles, my fellow researchers and I don’t want to stay at a cruising altitude of 35,000 feet. We want instead to know what is happening close to the surface of the ocean, below clouds, above clouds, and everywhere in between. The atmosphere contains different amounts and types of aerosol particles at every altitude level, so we need to fly at numerous altitudes each flight to understand that day’s atmospheric profile. Additionally, both local and international meteorology influence the composition of the atmosphere. For example, dust from the Saharan Desert can get picked up by strong winds and carried all the way over to the U.S. East Coast. This can blend with emissions from domestic power plants and ships to create a mixture of aerosol particles throughout the troposphere. With the help of all of the instruments onboard the Guardian Falcon, we can sample gases, collect cloud water, and count particles to quantify the relative atmospheric abundance of different particle types and begin to trace an air mass back to its source.

A couple of hours after our small team of graduate students stepped onto the Guardian Falcon, we watched it take off from the coastal Virginia airstrip, then headed inside the research center to the “war room,” where the daily team meetings took place for the three-year Aerosol Cloud meTeorology Interactions oVer the western ATlantic Experiment (ACTIVATE) campaign. Field campaigns are an extended period of data collection aimed at answering a science question posed by the government or national organization.

While the moniker “war room” may elicit an image of a dark, foreboding, cold, and uncomfortable dungeon, this planning room was totally ordinary: big windows, a long table filled with various laptops, and multiple projector screens displaying various maps and weather forecasts. Like a room for planning a battle, this is the room where meteorologists and engineers strategize and make all their major decisions for a flight—the most important being the flight path. Using meteorological forecasts, the team meets to decide where they want the pilots to fly (depending on what air masses they want to try to sample) and the best way for the pilots to get there. The heart of the post-flight work is the data analysis, where I get to put on my detective hat again.

There are six main stations onboard the Guardian Falcon, with each station recording information such as gases and aerosol composition. Each station outputs spreadsheets with thousands of rows of data for every flight. As an investigator and researcher, I identify the type of information I need for my case and gather the appropriate spreadsheets. From there, I use programming languages like Python and MATLAB to write code to run calculations, make graphs, and generally analyze the data. Imagine, in a less glamorous way, the work I am doing is like pinning up pictures of criminals, dilapidated buildings, and key items of interest on a very overused corkboard and connecting them with red string. I am trying to find the details to explain different scenarios, like the composition of the atmosphere in a certain part of the world. Sometimes, I find an interesting trend or an unexpected result. For example, say we found there was a pocket of industrial emissions in a “clean marine” area, which is an area over the ocean with no outside contamination like ships or continental pollution, but we had only expected to find sea salt. I would then have to go to a global particle transportation model to look for where this pollution came from, go back to our archive of data to pull information on sulfate, ammonium, and black carbon, and start my whole detective process over again—as when a detective has an “aha” moment and uses a previously discarded piece of information to rearrange the red strings to finally connect everything together.

When I stepped into a commonplace United Airlines aircraft a couple of days later, I admit I was slightly disappointed to see the plane filled with people and not aerosol sampling equipment. I settled into my window seat and let my mind wander as we left Virginia. The sun had started its descent and the wispy, white clouds provided a beautiful juxtaposition to the sunset. I appreciated how there was enough room for me to store my carry-on bag overhead and to stretch my legs—not the luxuries that the crew onboard the Guardian Falcon had. I absentmindedly pulled up a picture on my phone of me and another member of my research team beaming at each other, pretending to be the flight scientists at the two aircraft workstations. While I was sad to leave the heart of the action in Virginia, I was returning to Arizona a better scientist and detective. I had a new appreciation and respect for where my data had come from and how far it had traveled from that beautiful, strange plane to get to me.