200 apps and a backpack full of sensors—confronted the threat in person. For eight hours, they tracked (and breathed the air within) a 1.5-mile-high plume of ozone moving downwind across Long Island Sound and the Connecticut shoreline, at pollution levels above what the EPA deems hazardous. “A lot of pollution can be transported from the source region a long distance, affecting the chemistry and pollution somewhere else,” Liu said. The other major threat PM2.5, made of microscopic particles that can enter the bloodstream and cause heart and lung disease, strokes, and even premature death. After years of decline, PM2.5 started increasing again around 2016. When AQI values for NO2 or PM2.5 are above 100, air quality is unhealthy, according to the EPA—first for certain sensitive groups of people and then for everyone as AQI values get higher. TEMPO can’t directly measure PM2.5. And it has other limitations too, Liu points out. Pollution varies by altitude, but TEMPO only measures the columns of air it can detect from above. And it doesn’t work with cloudy skies or at night. (In the dark, TEMPO will be used to measure light pollution.) Still, TEMPO’s more precise data on location and chemistry will help build better pollution models and forecasts. Ongoing advances in artificial intelligence could extend the data even further, Liu said. “There’s a lot of interest in using AI and machine learning algorithms [with TEMPO data] to produce source especially major cities. Nitrogen dioxide (NO2) is the major culprit. Emitted by the burning of fuel and wildfires, industrial activities, and agricultural fertilization, NO2 is a key ingredient in ozone pollution and fine particulate matter. Ozone high in the atmosphere—the ozone layer—protects Earth from dangerous solar radiation, but ground-level ozone, a main ingredient in smog, aggravates respiratory diseases. And as it moves through the air, NO2 can be particularly hard to measure with existing monitoring stations. That point was driven home in June 2024, when TEMPO was powered on. That same day, Liu got an alert from the Smithsonian Institution as the smoke of Canadian wildfires descended on Washington, DC, and other cities across the northeast. On one hot July day in 2024, thousands of miles below TEMPO, on the streets of New York, teams of field researchers helping validate and enhance TEMPO’s data—and armed with Eventually, TEMPO 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.
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