198 These instruments combine with ground stations to inform measurements such as the Environmental Protection Agency (EPA) air quality index (AQI). But—as wildfire smoke reminded millions of people in North America last summer—these readings can still be imprecise and arrive too late. As NASA’s first earth-observation instrument located in geostationary orbit, TEMPO, or Tropospheric Emissions: Monitoring of Pollution, sits far higher up than existing satellites and remains over a single point on Earth, allowing it to see more pollution for longer. It can take 10 to 14 scans daily, from Canada’s oil sands to Mexico’s Yucatán Peninsula, from the Atlantic Ocean to the Pacific Ocean. (TEMPO is collaborating with an international team of scientists from Canada, Cuba, Mexico, and the US.) That rhythm, of imaging Earth at a blistering pace of about once an hour, helped give the instrument its name. “Basically, it’s going to sit over the equator and scan over North America, east to west, over and over,” said Liu. “Like the tempo of a musical instrument.” Alongside its frequency and unusual height, TEMPO’s big innovation is its spectrometer. By detecting tiny differences when sunlight hits molecules in the atmosphere and gets absorbed at specific wavelengths, spectrometers allow scientists to measure concentrations of trace gases in the troposphere, the innermost part of the atmosphere. But while other space-based spectrometers in the US can only see gas concentrations at a resolution of, at most, the size of a city, TEMPO can see down to about four square miles, or about the size of the Washington Mall. Eventually, say TEMPO scientists, its data could help displace our fuzzy pollution maps with something far more detailed and accurate, like a near real-time 3D video of the air. “Now we’re able to see small, individual point sources in each city and hourly measurements for highways, with variations from hour to hour. We’re able to see a lot of details at the neighborhood scale.” — Xiong Liu, senior physicist and TEMPO’s deputy principal investigator at the Smithsonian Astrophysical Observatory and a member of the Center for Astrophysics | Harvard & Smithsonian Harming Vulnerable Communities the Most The EPA, the US Forest Service, and others have tried to enhance pollution maps by incorporating data from a growing community of citizen air watchers. But there aren’t enough devices—the community-managed air monitors tend to be in wealthier communities—and they aren’t sampled frequently enough to generate accurate, reliable pollution forecasts. And along with existing space-based sensors, community-managed monitors can provide only a limited portrait of how pollution moves in different weather conditions, for instance, or the ways it impacts the most vulnerable populations the hardest. Bad air—ground-level ozone pollution and fine particulate matter (PM2.5)—leads to more than 100,000 premature deaths and billions of dollars in annual damages in the US, according to the National Weather Service. Liu cited stats from the American Lung Association’s 2023 State of the Air report: “One-third of the American population is still affected by unhealthy air pollution,” he said. “And people of color are The Smithsonian and NASA have teamed to create TEMPO, a new air pollution sensor that’s now returning remarkable awareness. (Image courtesy of the Tempo mission)
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