An empty airport tells you more than you might think.

With the spread of COVID-19 limiting takeoffs, researchers are using sensors to better understand how coronavirus-related travel bans and lockdown orders are impacting air quality around airports. The scientific instruments, which are part of NASA’s Pandora Project , identify harmful chemicals in the air.

To record the atmospheric observations, Dr. Jennifer Kaiser at Georgia Institute of Technology in Atlanta and Elena Lind at Virginia Polytechnic Institute in Blacksburg placed sensor instruments at two airports: Baltimore-Washington International Airport (BWI) and Hartsfield-Jackson Atlanta International Airport.

BWI’s overall traffic has decreased by approximately 60 percent, and Atlanta’s departures have declined by 70 percent.

The Pandora Project, begun in 2005, implements ground-based spectroscopy instruments to determine atmospheric interactions and composition. One of Pandora's major objectives is to validate the environmental observations made from sensing satellites in low-earth orbit, like the Sentinel 5P .

The airport spectrometers, each propped up with a tripod, use ultraviolet and visible wavelengths of light to detect ozone, nitrogen dioxide, and formaldehyde at different altitudes of the atmosphere.

Airports are usually some of the hottest spots for nitrogen dioxide, says Kaiser, as the gas is released when airplanes burn large amounts of fuel. Nitrogen dioxide reacts with other chemicals and forms ozone, which can cause chest pain, coughing, and throat irritation.

Kaiser is comparing the on-the-ground sensor data with satellite information from the European Space Agency (ESA)’s TROPOspheric Monitoring Instrument  (TROPOMI), aboard the Copernicus Sentinel-5 Precursor satellite. Launched in 2017, Copernicus is managed by the European Commission in partnership with ESA, the EU Member States, and EU agencies.

The airport observers want to verify satellite observations by "ground-truthing" them with the newly-installed Pandora sensors.

"We want to help our stakeholders, like policymakers, improve their understanding of the air we breathe," said Kaiser in a recent press release . "People are looking at COVID-19 impacts and seeing better air quality with less traffic. They might wonder if this is what the future could look like if we relied more heavily on electric vehicles than we do now."

Observations began near the airports in early April. The data is just now coming in, and all environmental factors must be considered before determinations are made about air quality, says the Georgia Tech researcher.

"It will be important to figure out the role of meteorology in shifting pollutant concentrations and vertical profiles before arriving at any conclusions," Kaiser told Tech Briefs.

In a short Q&A with Tech Briefs below, Kaiser explains why satellite data, combined with ground-based instruments, gives us a more complete picture of air quality.

Tech Briefs: When did the Pandora Project begin, and what are its objectives?

Dr. Jennifer Kaiser: ​The Pandora project  began in 2005. It has grown into a large, collaborative effort with instruments deployed across the globe. A main objective is to provide a vast spatial network which can be used to better understand satellite-based observations.

Tech Briefs: Why was the Pandora Project well suited to give us information about the effects of lockdown orders and travel bans?

Kaiser: Pandora instruments are especially well suited for measuring the total amount of pollution in a vertical column (as opposed to only ground-level concentrations). This is comparable to the information satellites provide. So while satellite-based observations give us a more spatially complete picture of what's happening to pollution in near-real time, the Pandoras can be used to ground-truth the observations at specific locations.

Our study focuses on airports. Flight numbers are drastically lower than the pre-COVID world, and we anticipate that satellite-based observations will be able to see the changes in air quality near airports world-wide.

Tech Briefs: Why are airports such a valuable location to study?

Kaiser: Airports are especially interesting because the vertical distribution of pollutants may be different than those near an urban core. Estimates of that vertical distribution are baked into the satellite retrievals. In addition to total columns, Pandora instruments can piece out vertical distributions. This allows us to test and refine our initial estimates.

Tech Briefs: What kinds of instruments make these conclusions possible?

Kaiser: SciGlob , [a science and engineering company based in Elkridge, MD], makes and distributes Pandora instruments. We were lucky enough that the labs are just a short distance from BWI. The instruments were already there, we just needed to point them in the right direction!

The ATL measurements are generously hosted by the Georgia Environmental Protection Division. It just so happened that they are also located extremely close to the airport, and had an unused measurement facility that could support our work.

A map of average tropospheric nitrogen dioxide (NO2), March 15-April 15 2020, southeast U.S. (Credit: NASA's Scientific Visualization Studio)
A map of average tropospheric nitrogen dioxide (NO2), March 15-April 15 2015-2019, southeast U.S.. (Credit: NASA's Scientific Visualization Studio)

Tech Briefs: What can these conclusions teach us about the best policies to enact going forward, and the best ways to go about our lives?

Kaiser: We don't have any conclusions yet. My hope is that these observations will help with the interpretation of satellite data and our understanding of airport-related pollution so that policy makers can do their job with the best available information.