Satellite network will monitor air pollution in near real time | Science

The eastern flank of Colorado’s Rocky Mountains traps a confusing swirl of air pollution. Emissions from oil and gas wells to the north mix with car exhaust from the Denver area and sporadic wildfire smoke. Winds flow up and down the mountainsides like tides, sweeping away and returning the smog. Pinning down the sources of the pollution and understanding its hour-by-hour behavior is “very, very complicated,” says Gabriele Pfister, an atmospheric scientist at the National Center for Atmospheric Research.

Pfister should soon have a much clearer picture, thanks to a NASA sensor scheduled for launch on 7 April. She is one of many pollution watchers eagerly awaiting the Tropospheric Emissions Monitoring of Pollution (TEMPO) instrument, which is mounted to a commercial communications satellite. It will hover 36,000 kilometers above North America, orbiting in sync with Earth’s rotation.

TEMPO is one of three geostationary instruments that together will create the first network dedicated to monitoring air pollution across much of the Northern Hemisphere. With TEMPO, scientists who have relied on once-a-day snapshots from orbit will soon have hourly images for most of North America, from smog-choked Mexico City to northern Canada’s oilsands. “It brings significantly more observations into the game than we had so far,” Pfister says. “And more observations mean we can have a better understanding of what is happening.”

TEMPO’s sensors detect tiny differences in the light reflected when sunlight strikes molecules in the atmosphere and gets absorbed at specific wavelengths. It can track ozone, nitrogen dioxide, sulfur dioxide, bromine, and organic molecules such as formaldehyde, as well as tiny airborne particles called aerosols. It will measure pollutants on a fine grid of 2.1 by 4.5 kilometers, helping scientists trace them to sources such as smokestacks, exhaust pipes, and volcanoes.

In regions that don’t meet air quality standards, TEMPO could help improve forecasts used for public health alerts. The Denver area struggles to control ground-level ozone, which is linked to increased rates of asthma and other respiratory diseases. Today, Pfister relies on computer models paired with scattered data from satellites and air quality ground stations to estimate pollution levels. She hopes TEMPO will help fill in the blind spots and improve models of the sources of nitrogen dioxide, a key ingredient in ozone.

Such observations could also help scientists firm up links between air pollution and health, says Allan Just, an environmental epidemiologist at the Icahn School of Medicine at Mount Sinai. He was part of recent work correlating air pollution in Mexico City to death rates. The research relied on scarce monitoring stations and a single satellite image a day to estimate how much air pollution people are really breathing. That “isn’t enough to keep track of how things could be really changing at the ground level,” Just says.

TEMPO won’t directly measure one of the most harmful air pollutants—fine soot known as PM2.5. But scientists are working to convert the sensor’s broader measurements of aerosols into a PM2.5 estimate using models and data from air monitors on the ground, says Aaron Naeger, an atmospheric scientist at the University of Alabama, Huntsville, and a lead scientist on the TEMPO mission.

TEMPO will join South Korea’s Geostationary Environmental Monitoring Spectrometer (GEMS), which launched in 2020 and looks down on most of Asia. And in 2024, the European Space Agency is expected to launch Sentinel-4, an air pollution tracker that will focus on Europe.

So far, the GEMS satellite has delivered a view of the daily rhythms of nitrogen dioxide pollution across much of Asia. Nitrogen dioxide peaks in the morning in Beijing, for example, and in the afternoon in Shanghai. GEMS has also tracked air-fouling dust storms from northern China and climate-cooling sulfur dioxide from volcanic eruptions. “GEMS has revolutionized air quality observations,” says Jhoon Kim, an atmospheric scientist at Yonsei University who is the principal investigator for the GEMS mission.

Once complete, the trio of instruments will still have a big blind spot: the Southern Hemisphere. Although the network could in theory have nearly covered the globe, the instruments were built to zoom in on the Northern Hemisphere, says Harvard University atmospheric scientist Daniel Jacob, who is collaborating with both the GEMS and TEMPO teams. In part that reflects a “parochialism” among the countries building the instruments, says Jacob, who laments what will be missed. “All of the tropics are not going to be observed,” he says. As tropical megacities rise, “this is where we’ve got the most serious air pollution problems brewing.”

The eastern flank of Colorado’s Rocky Mountains traps a confusing swirl of air pollution. Emissions from oil and gas wells to the north mix with car exhaust from the Denver area and sporadic wildfire smoke. Winds flow up and down the mountainsides like tides, sweeping away and returning the smog. Pinning down the sources of the pollution and understanding its hour-by-hour behavior is “very, very complicated,” says Gabriele Pfister, an atmospheric scientist at the National Center for Atmospheric Research.

Pfister should soon have a much clearer picture, thanks to a NASA sensor scheduled for launch on 7 April. She is one of many pollution watchers eagerly awaiting the Tropospheric Emissions Monitoring of Pollution (TEMPO) instrument, which is mounted to a commercial communications satellite. It will hover 36,000 kilometers above North America, orbiting in sync with Earth’s rotation.

TEMPO is one of three geostationary instruments that together will create the first network dedicated to monitoring air pollution across much of the Northern Hemisphere. With TEMPO, scientists who have relied on once-a-day snapshots from orbit will soon have hourly images for most of North America, from smog-choked Mexico City to northern Canada’s oilsands. “It brings significantly more observations into the game than we had so far,” Pfister says. “And more observations mean we can have a better understanding of what is happening.”

TEMPO’s sensors detect tiny differences in the light reflected when sunlight strikes molecules in the atmosphere and gets absorbed at specific wavelengths. It can track ozone, nitrogen dioxide, sulfur dioxide, bromine, and organic molecules such as formaldehyde, as well as tiny airborne particles called aerosols. It will measure pollutants on a fine grid of 2.1 by 4.5 kilometers, helping scientists trace them to sources such as smokestacks, exhaust pipes, and volcanoes.

In regions that don’t meet air quality standards, TEMPO could help improve forecasts used for public health alerts. The Denver area struggles to control ground-level ozone, which is linked to increased rates of asthma and other respiratory diseases. Today, Pfister relies on computer models paired with scattered data from satellites and air quality ground stations to estimate pollution levels. She hopes TEMPO will help fill in the blind spots and improve models of the sources of nitrogen dioxide, a key ingredient in ozone.

Such observations could also help scientists firm up links between air pollution and health, says Allan Just, an environmental epidemiologist at the Icahn School of Medicine at Mount Sinai. He was part of recent work correlating air pollution in Mexico City to death rates. The research relied on scarce monitoring stations and a single satellite image a day to estimate how much air pollution people are really breathing. That “isn’t enough to keep track of how things could be really changing at the ground level,” Just says.

TEMPO won’t directly measure one of the most harmful air pollutants—fine soot known as PM2.5. But scientists are working to convert the sensor’s broader measurements of aerosols into a PM2.5 estimate using models and data from air monitors on the ground, says Aaron Naeger, an atmospheric scientist at the University of Alabama, Huntsville, and a lead scientist on the TEMPO mission.

TEMPO will join South Korea’s Geostationary Environmental Monitoring Spectrometer (GEMS), which launched in 2020 and looks down on most of Asia. And in 2024, the European Space Agency is expected to launch Sentinel-4, an air pollution tracker that will focus on Europe.

So far, the GEMS satellite has delivered a view of the daily rhythms of nitrogen dioxide pollution across much of Asia. Nitrogen dioxide peaks in the morning in Beijing, for example, and in the afternoon in Shanghai. GEMS has also tracked air-fouling dust storms from northern China and climate-cooling sulfur dioxide from volcanic eruptions. “GEMS has revolutionized air quality observations,” says Jhoon Kim, an atmospheric scientist at Yonsei University who is the principal investigator for the GEMS mission.

Once complete, the trio of instruments will still have a big blind spot: the Southern Hemisphere. Although the network could in theory have nearly covered the globe, the instruments were built to zoom in on the Northern Hemisphere, says Harvard University atmospheric scientist Daniel Jacob, who is collaborating with both the GEMS and TEMPO teams. In part that reflects a “parochialism” among the countries building the instruments, says Jacob, who laments what will be missed. “All of the tropics are not going to be observed,” he says. As tropical megacities rise, “this is where we’ve got the most serious air pollution problems brewing.”