While most people Could be attracted by the perpetually sunny sky, the nearby ocean, or the mountains that embrace the Los Angeles basin, environmental engineer Annmarie Eldering was attracted by the smog of the city. “It’s the best place to go,” she says. “You have tons of pollution!”
Urban areas release more than 70 percent of man-made carbon dioxide emissions that are released into the atmosphere, and LA is no exception. With more than 13 million residents in its largest metropolitan area, a sophisticated highway network, and an international transportation hub, LA produces the fifth most CO2 of all the cities of the world. This makes it a sweet place to study the role of man in climate change.
Eldering is the project scientist for NASA’s Orbiting Carbon-3 Observatory, or OCO-3, an instrument that measures atmospheric CO2 levels from space to better understand the impact of human activity on the natural carbon cycle, the process by which plants, land, oceans, and the atmosphere exchange carbon between them. In a paper published this month, Eldering and colleagues published a paper showing the most detailed variations of CO2 emissions over the LA basin never seen from space. This research shows that space-based monitors can be used to collect large chunks of data on pollution hotspots, information that could help inform policy to combat climate change.
“What’s exciting about the OCO-3 result is that this is the first time we’ve got this kind of area map on a city like LA from space,” says Joshua Laughner, a postdoctoral fellow in Caltech working on a global ground-based surveillance system called the Total Coal Column Observation Network. While they are useful for observing precisely how atmospheric carbon concentrations change over time, instruments such as the TCCON are expensive to manage and require partnerships with qualified scientists, so their data collection is limited to specific areas. An observatory in orbit, on the other hand, can scan parts of the planet that are difficult to study from the ground, such as volcanoes or cities with high-carbon footprints but few surveillance resources.
Launched in 2019, OCO-3 is now mounted on the International Space Station, where it will see almost every city on Earth in an average duration of three days, according to a NASA press release. It’s an improvement over its ever-active predecessor, OCO-2, which can only collect a 10-kilometer-wide data band and is locked in a synchronous orbit of the sun that passes over LA at the same time each day, meaning which can verify only the atmospheric CO of the city2 levels at 1:30 in the afternoon.
“With OCO-3, we have much better spatial coverage, as well as temporary coverage, so you can now look at the city at different times,” says Dalt Wu, a Caltech postdoctoral scholar who works closely with the team in the analysis of urban emissions. OCO-3 can do more sweeping on a single location, drawing a snapshot of about 80 square miles in just two minutes.
The color of each pixel above this card created by the Eldering team represents atmospheric CO2 concentration in an area on land that is about 1.3 miles wide. Because carbon dioxide absorbs certain wavelengths of light, scientists can use this information to deduce how much is present in the Earth’s atmosphere. OCO-3 observed changes in the intensity of the sun as it passed through a vertical column of air and created a reading for how much CO2 he was in that place.
Next, the OCO-3 team compared these satellite data to “clean air” readings already collected by a ground-based TCCON instrument at NASA’s Armstrong Flight Research Center in the desert north of LA, far from and local emission sources. It uses a baseline of about 410 parts per million (or 410 CO.)2 molecules per million molecules of dry air), OCO-3 was able to identify the differences up to an average part per million. They have seen excessive amounts of CO2 at more than five parts per million over the LA basin. It may seem small, but it is equal to the amount that these emissions grow on a global scale every two years.