Factory smokestacks belch plumes of chemicals. Roaring wildfires saturate the skies with a smoky haze. Clouds of tailpipe emissions waft from roadways. Each day, these and many other sources add to a stew of air pollutants harmful to human health and the environment—and it’s a problem that’s not always easy to spot.
But thanks to a collaboration between NASA and the Smithsonian Astrophysical Observatory (SAO), part of the Center for Astrophysics | Harvard & Smithsonian, a revolutionary new tool will soon offer a more detailed analysis of air pollution that will keep an eye on the air we breathe from more than 22,000 miles above the ground.
The satellite-based Tropospheric Emissions: Monitoring of Pollution (TEMPO) instrument will monitor the chemistry and changing dynamics of many major pollutants hourly, at extremely detailed resolutions. TEMPO will track the ways air pollution is created, and how it evolves and disperses, throughout the atmosphere and across the entirety of North America.
“TEMPO is a satellite mission that consists of a spectrometer, using technology that we’ve been developing for more than 30 years, to use the spectrum of light to measure air pollution,” explains Kelly Chance, the project’s principal investigator with SAO, who first proposed the mission a decade ago. “We have a sort of motto that says, ‘TEMPO: It’s about time.’ But it means that we measure North America hourly during the daylight hours, at a spatial resolution a little larger than the [National] Mall in Washington, D.C.”
Launch from Florida’s Cape Canaveral Space Force Station is slated for April, when a Falcon 9 two-stage rocket will lift off and, at 7,000 miles per hour, deliver its satellite payload to geostationary orbit, meaning the satellite will maintain a position 22,236 miles directly over the United States, Mexico and Canada. TEMPO’s washing machine-sized suite of instruments, resembling a framework of tubes topped with a disc-shaped turntable, will be housed on the Earth-facing side of a massive Intelsat 40e communications satellite.
“Down here where we live, in the air that we breathe, there’s a lot of different things to be concerned about,” notes Kevin Daugherty, a project manager at NASA’s Langley Research Center in Hampton, Virginia. “Getting this high resolution … all the way across the country, I think, is going to be a really big step forward in being able to piece together where our major sources of pollution are and how that pollution moves.”
Air pollution is dramatically impacted by weather of all types; wind distributes pollutants, rain can wash them away, warm air and sunshine can spark or speed up chemical ratios in the air. Lightning can generate nitrogen oxides, which are associated with the formation of harmful ozone. TEMPO’s tracking will reveal the interactions between weather and atmospheric pollutants like never before, to the benefit of scientists, citizens who hope to avoid bad air quality days and even those tasked with improving the air we breathe.
“When managers are trying to figure out how to most effectively clean up the air quality, having that understanding of what’s going on in their area, on a particular day, under a particular set of conditions. That’s the information they need to make the most effective decisions,” says Arlene Fiore, an atmospheric and planetary scientist at MIT, who is not associated with the project.
“TEMPO will measure atmospheric pollution every daylight hour from the Atlantic to the Pacific, and from Puerto Rico and Mexico City to the Canadian oil sands in Alberta,” says Chance.
The satellite’s continental coverage will also be in tremendous local detail, with a spatial resolution of four square miles, representing an enormous upgrade from current satellite capabilities of roughly 155 square miles. The fine focus will help directly identify which areas have higher or lower levels of pollution, and spot the specific sources of different air pollutants such as factories or farms.
Most orbiting air-quality-monitoring systems observe air pollution at a particular location just once a day, and usually at the same time, as they pass over while circling the Earth. But air pollution, whether from vehicles, power plants or wildfires, is emitted at many different times. Pollutants are also dynamic; they are quickly transported by winds to locations away from their sources, and they undergo chemical reactions when airborne. Current satellites lack the ability to keep track of this ever-changing atmospheric milieu.
“We’re aware that at certain times of the day it’s higher, and at other times it’s lower,” says Daugherty. “Existing satellites can’t really see how the pollution is changing throughout the day, and might even miss the peak of the pollution. Being able to scan every daylight hour, we’ll be able to see those effects as it comes and goes throughout the day.”
The NASA-funded mission will measure pollution concentrations of ozone, nitrogen dioxide, sulfur dioxide, formaldehyde and aerosols in the troposphere—the lower atmosphere from the Earth’s surface to about 10 miles up. These hourly reports will help model sources and movements of pollution, and how our atmosphere is changing, in real time and over longer periods of time.
By tracking evolving variations in air pollutants throughout the day, a kind of “chemical weather,” TEMPO will deliver data that can produce air quality forecasting across the continent to alert the public when levels of particulate matter, volatile organic compounds, nitrogen dioxide or other chemicals make the air especially unhealthy. Ground-based sensors enable these kind of alerts in some major urban centers, based on the U.S. Environmental Protection Agency (EPA) Air Quality Index, but people in most of North America have no such resource to know when their local air is clean.
The team envisions practical use measures like a cellphone app for people who are sensitive to air pollutants, who would be able to use the data in real time. “One of the things that we hope to do is to have people look up the air quality where they are and be able to open an app and ask, ‘Can I go for a run this morning?’” says Chance.
TEMPO, described as an orbiting atmospheric chemistry lab, employs a spectrometer sensitive to both visible and ultraviolet wavelengths. The system’s light-collecting mirror will make a complete east-to-west scan of the continent every single daylight hour. Different pollutants will be viewed through the sunlight reflected from the Earth back to TEMPO’s detecting instruments by the way they absorb frequencies from sunlight.
“We are carefully looking at that light and measuring with such accuracy that we can piece out what types of molecules it came from,” says Daugherty. By identifying the where, what and when of air pollution in tremendous detail, TEMPO will help guide policy makers hoping to mitigate the harmful effects of pollution at the source.
TEMPO is the first of NASA’s Earth Venture Instrument programs—small, targeted science investigations designed to complement the agency’s bigger research missions. Working with SAO’s Chance is a top-notch science team including experts from NASA’s Langley Research Center and Goddard Space Flight Center, the National Oceanic and Atmospheric Administration, Ball Aerospace and the EPA.
The project is also a valuable commercial partnership. The communications satellite housing TEMPO, built by Maxar in Palo Alto, California, will provide Intelsat’s commercial aviation customers with more than 40 gigabytes per second of internet connectivity while it flies over North America. Those same capabilities will be tapped by the TEMPO mission, a partnership that saved millions of dollars compared to the cost of launching TEMPO aboard a standalone spacecraft.
And TEMPO’s continental scale is only part of a larger picture. The satellite joins a constellation of pollution-monitoring satellites, including one launched by the Korea Aerospace Research Institute in 2020 and one the European Space Agency plans to set in motion next year. Together, this air quality constellation will scan Europe, North America and Asia, and track air pollution across many of the world’s population centers, from neighborhood to intercontinental scales.
Daugherty says a massive California wildfire would be a prime opportunity to leverage TEMPO’s unique capabilities. Such fires create significant air pollution for people living in the surrounding areas, but that’s only a small part of the picture—wildfire pollution also travels the air currents, spreading far from the source, researchers have found.
“It’s important to understand how these sources are generating pollution and where pollution is being transported,” Daugherty explains. “One of the things we’ll be able to do is actually see some of that moving, track it as it flows across the country.”
And when an exceptional and dynamic source of pollution flares up, like a volcanic eruption or an industrial accident, TEMPO can shift gears to capture the event, allowing analysis of its unique pollution signature in tremendous detail. “We can focus in on a smaller area, just one-sixth the size of the continent, and then produce scans every ten minutes,” Daugherty explains.
The plan is for TEMPO to routinely monitor more common sources of air pollution, keeping track in tremendous detail of the ebbs and flows of pollutant production emitted from factory facilities and rising from rush hour traffic. Those repeated observations will reveal patterns, such as which weather conditions might cause more nitrogen oxide pollution after farm fertilization.
TEMPO is also targeting ozone in the troposphere. Unlike upper atmosphere ozone, which acts as a protective shield to absorb damaging UV radiation produced by the sun, ozone in the air we breathe plays a role in the formation of smog and is damaging to human lungs.
Such ozone isn’t always easy to detect because it’s not produced directly but forms through chemical reactions involving sunlight in the atmosphere with key ingredients called nitrogen oxides and volatile organic compounds. “So the really neat thing about TEMPO is that it’s our first instrument that senses these species that are so relevant to the format of ozone, continuously throughout the daylight hours,” says Fiore.
Despite its high altitude, TEMPO will retrieve ozone readings from the ground to just 1.25 miles up, which haven’t been available in such detail before. For that advance, Chance credits the dedicated efforts of the project’s Deputy Principal Investigator Xiong Liu, a physicist at SAO and a leading expert in ozone pollution retrieval from space.
“The satellite is way up there, and seeing all the way down to here, where we’re sitting, is tough, because the atmosphere is complicated and there’s a whole bunch of it in between,” says Chance. “Measuring tropospheric ozone from satellites looking down is not an easy thing to do. But Xiong Liu did it.”
Even before launch, TEMPO’s capabilities have inspired scientists to suggest a score of other creative ways to employ the system. TEMPO might study the impacts of lightning on producing ozone, or how oceans and lakes produce chemicals that may deplete ozone. The system could chart atmospheric rivers, the airborne corridors of moisture that move enormous amounts of moisture, like the famed Pineapple Express that flows from Hawaii to the West Coast. The possibilities are vast, that's an exciting prospect.
“The funny thing is, there is more to the satellite and the science that I don’t know than I do know,” he says. “When good scientific instruments go up, they do so much more than people planned or even thought of.”