Portland’s Air Quality Crisis
In early August, the skies over Portland, Oregon, took on an increasingly familiar sepia hue as easterly winds carried plumes of gas and smoke from nearby wildfires into the city. At one point, Portland’s air quality was reported as the worst in the world, leading to the closure of summer camps and public swimming pools, as well as the cancellation of outdoor concerts. This summer, characterised by intense heat and wildfires, mirrored similar situations across cities in North America, including New York, Denver, Chicago, and Toledo.
Above it all, a NASA satellite observed the dynamic swirl of gases and particles that fuelled these air quality crises. Positioned at an altitude of 35,000 kilometres (22,000 miles) above the equator, the TEMPO (Tropospheric Emissions: Monitoring of Pollution) satellite has been providing hourly, near real-time snapshots of the pollutants that originate, migrate, and dissipate in the daytime atmosphere over North America since September 2025.
Unlike previous pollution-tracking satellites that captured only one or two images of air quality daily, this continuous continental view has significantly enhanced researchers’ and regulatory authorities’ understanding and response to some of the most unpredictable and uncontrollable atmospheric pollutants. TEMPO demonstrates that pollution, much like weather, is not static. “Pollution varies from hour to hour, day to day,” states Laura Judd, a NASA research scientist at the Langley Research Center in Hampton, Virginia. “What we get from TEMPO is this illustration of what we call ‘chemical weather’.”
Challenges in Reducing Air Pollution
Since the Clean Air Act was enacted in 1970, the United States has made substantial progress in reducing levels of six common hazardous air pollutants. However, the reduction of two specific pollutants – ozone and particulate matter smaller than 2.5 micrometres in diameter, known as PM2.5 – has stagnated over the past 15 years. Both are secondary pollutants formed through chemical reactions in the atmosphere influenced by sunlight, heat, and other variables.
Due to their complex chemistry and the fact that their precursors come from diffuse sources such as airports, agriculture, and wildfires, secondary pollutants have proven particularly challenging to understand and control. They remain significant contributors to approximately 100,000 premature deaths, 10,000 preterm births, and 200,000 cases of childhood asthma attributable to air pollution in the United States. Furthermore, a 2023 review in the Annual Review of Pharmacology and Toxicology highlighted increasing evidence that air pollution may contribute to neurodevelopmental disorders such as schizophrenia, as well as neurodegenerative diseases like Alzheimer’s and Parkinson’s.
Unlocking Potential with TEMPO
TEMPO’s ability to track how secondary pollutants form throughout the day holds substantial potential for reducing these alarming statistics. State and local governments can utilise TEMPO to identify and mitigate precursors, thereby helping them better comply with federal air quality standards. Scientists can develop predictive models for secondary pollutants and issue more timely alerts regarding hazardous air quality. Public health researchers can base pollution control measures on more accurate information about when and where secondary pollutants impact human health.
TEMPO collects data using a spectrometer that measures the absorption patterns of ultraviolet and visible light in the atmosphere, allowing for estimations of concentrations of nitrogen dioxide (NO2), formaldehyde, aerosols, and tropospheric ozone with a resolution of approximately four square miles (around 10 km²). The satellite fills the gaps left by the United States Environmental Protection Agency’s (EPA) ground monitoring system, which provides high-quality data but covers only about a third of the more than 3,000 counties in the United States.
“It represents a revolutionary change,” asserts Tracey Holloway, an atmospheric scientist at the University of Wisconsin-Madison and lead of NASA’s Air Quality Applied Sciences Team. “It will really change our perception of who is breathing what.”
The Impact of Wildfire Smoke
Last summer, across North America, that “what” was often the smoke from wildfires. Especially in the western United States, air quality districts constantly faced the tremendous impacts of devastating wildfires. A study revealed that 23% of PM2.5 in the atmosphere during the summer of 2020 originated from record-breaking wildfires. Consequently, there were 3,720 instances where the EPA’s National Ambient Air Quality Standards (NAAQS) for six key pollutants were exceeded.
TEMPO is aiding researchers in demonstrating precisely how smoke from distant wildfires transports the precursors of secondary pollutants across hundreds or thousands of miles, assisting air quality managers in determining when local sources are responsible for pollution spikes and when they are not.
“In smoke columns, there are always high concentrations of formaldehyde,” explains Shobha Kondragunta, a physical scientist at NOAA’s Center for Satellite Applications and Research in College Park, Maryland. This occurs because, in the presence of sunlight, volatile organic compounds break down to form this chemical. Subsequently, formaldehyde reacts with nitrogen oxides in the atmosphere to produce ozone and PM2.5. TEMPO tracks both precursors.
Enhancing Regulatory Responses
The satellite also enables researchers to estimate the height of smoke columns, which can help them calculate how much sunlight penetrates the haze and promotes the formation of ground-level ozone that people breathe. TEMPO’s hourly, high-resolution data also facilitates the documentation that agencies require to monitor the contribution of wildfire smoke to air quality, particularly over long distances. This could help avoid the imposition of unnecessary restrictions.
“We don’t want to declare an area as being in non-compliance due to wildfire smoke or dust storms, situations that a state can never resolve,” states Mary Uhl, executive director of the Western States Air Resources Council, an association of 15 air quality agencies from western states.
Amanda Fritz, an air pollution control engineer at the Connecticut Department of Energy and Environmental Protection in Hartford, notes that smoke columns from wildfires in Canada, hundreds of miles away, contributed this summer to many —though not all— of the 13 instances of ozone limit exceedances recorded in her state by July 4, marking the earliest date the region has reached this alarming milestone. Ozone has always been an issue in Connecticut due to smog drifting northeast from New York City. Even a small amount of smoke can provide just enough additional precursors to trigger an exceedance of ozone limits.
Identifying Local Ozone Sources
With TEMPO, researchers can ascertain “where the ozone is being produced,” says Jennifer Kaiser, an air quality researcher at the Georgia Institute of Technology in Atlanta. “We’ve never before measured ground-level ozone from a satellite,” she adds. This information can highlight key local sources of ozone precursors that regulatory authorities can then target for action.
TEMPO has already assisted air quality managers in Maryland in understanding how local factors combine to generate harmful air and prevent their jurisdictions from meeting air quality standards. In 2022, Maryland met all NAAQS for the first time. However, this year, the state had already recorded 10 days of ozone exceedances by August.
Given the fragility of this state achievement, Joel Dreessen, an air quality meteorologist at the Maryland Department of the Environment, utilised TEMPO to determine the origins of ozone masses. Since ozone formation intensifies with high temperatures, Dreessen and his colleagues compared TEMPO’s NO2 data on hot mornings with and without ozone peaks. They found that NO2 was a key determinant in local ozone formation, with sources primarily from industrial areas and the heavily trafficked Interstate 95 corridor.
Real-time Monitoring in Urban Areas
Iván Gutiérrez Ávila, an environmental medicine professor at the Icahn School of Medicine at Mount Sinai in New York, has found that TEMPO measurements of NO2 peak during the morning rush hour in Mexico City, the most populous city in North America, located in a mountainous valley that naturally traps atmospheric pollutants close to the ground. Prior to TEMPO, the best available satellite estimates of NO2 only provided one reading per day, in the early afternoon.
“If we use information that isn’t most relevant to exposure, we will miss important details for health epidemiological models,” indicates Allan Just, Gutiérrez Ávila’s colleague and an environmental epidemiologist at Brown University in Rhode Island.
Moreover, Gutiérrez Ávila and Just have demonstrated that emergency room visits increase during NO2 peaks, providing authorities with useful information about the relationship between exposure and health effects. “Communities need to be able to make decisions: should we cancel the football match, move recess indoors, or advise people to take protective measures outdoors?” Just emphasises.
Empowering Communities with Air Quality Data
Nasa aims for citizens to utilise TEMPO. To this end, Erika Wright, an education specialist at the Smithsonian Astrophysical Observatory near Boston, assisted in designing TEMPO Lite, an online mapping tool accessible to anyone. TEMPO Lite provides satellite NO2 data on an interactive map that allows users to observe continental-scale patterns throughout a day or delve deeper to investigate the local impacts of traffic, wildfires, industrial