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In the spring of 2023, the Center for Astrophysics | Harvard & Smithsonian and NASA are launching a scientific instrument into space dedicated to measuring air quality across the United States. Just like how weather satellites measure precipitation and temperature, this new instrument, called TEMPO, will measure all the major air pollutants across North America every hour in high resolution. But TEMPO is not the only space-based scientific instrument built for monitoring air quality. In 2020, South Korea shot its Geostationary Environment Monitoring Spectrometer (GEMS) instrument into space, which is already collecting data on air quality across much of Asia. Then, in 2024, the European Space Agency is sending its Sentinel-4 satellite into space to measure air quality over Europe and North Africa. Together, these three instruments and their low Earth orbit counterparts will collect a global constellation of data about air quality to help scientists understand the causes, movement, and effects of air pollution across some of the world’s most populated areas.

These three instruments are not the first to measure air quality from space. Early air quality instruments circled the Earth once per day in line with the sun, which meant they could only measure air quality over a particular region every 24 hours. The GEMS, TEMPO, and Sentinel-4 instruments, in contrast, will sit in geostationary orbit, which means they revolve in line with the Earth, allowing them to remain over their target regions and measure air quality once per hour during daylight hours. Each instrument will feature similar capabilities, but scientists will use them differently as they study the pollutants and other atmospheric conditions of greatest concern to each region.

GEMS in Asia

According to a recent analysis, every person in South Korea breathes unhealthy air every day, reducing national life expectancy by more than six months. GEMS will help South Korea address the pollutants that contribute most to this problem, including aerosols and ozone. Gases such as nitrogen dioxide are produced by burning fossil fuels and they threaten the environment and human health in many ways. For example, some degrade the stratospheric ozone layer that protects Earth from harmful UV radiation, and they also serve as ingredients for ground-level ozone that irritates the lungs and can cause breathing difficulties in people with emphysema and asthma. Some pollutants, including ozone can travel long distances; therefore, the pollutants that affect South Korea may be produced locally or may come from neighboring countries. GEMS’ wide field of view allows it to monitor some of the largest pollution emitters in the world, including China and India.

TEMPO Across North America

Once it reaches geostationary orbit in space, TEMPO will begin monitoring air pollution across North America, from southern Mexico to northern Canada and from the Atlantic to the Pacific. The U.S., specifically, is the second largest polluter in the world behind China. Air quality is worsening in the western United States due to more frequent wildfires among other environmental factors, leading to spikes in hospital visits for respiratory issues. For example, in September 2020, amid a spate of wildfires in the Cascade Mountains in Oregon, hospitals in the state reported a 38% increase in emergency room visits due to respiratory issues compared to the previous month.

TEMPO will help scientists to address several questions about the origin of air pollution caused by wildfires as well as human activity and how it affects environments and people all over the continent. Scientists will use TEMPO to measure the environmental impacts of automobile emissions during rush hour in urban and suburban areas and biomass burning in forest, grassland, and agricultural areas. It will also track emissions from oil and gas fields, drilling platforms, and ships. Other unique agricultural applications for TEMPO include assessing the extent to which water released from corn and the soil worsens heat waves and contributes to air pollution in the Midwestern United States. Scientists could also potentially use the instrument to measure the release of nitrogen oxides from farms, which happens when it rains shortly after farmers apply fertilizer to their fields.

With these data, scientists will be able to forecast air quality throughout the day, just like the weather, to serve public health and inform policymakers about changes they could implement to reduce air pollution across the continent.

Sentinel-4 for Europe and Northern Africa

Expected to launch in 2024, the Sentinel-4 satellite from the European Space Agency (ESA) will measure air quality over Europe and Northern Africa. This region faces many of the same air pollution threats as North America and Asia, including ozone and nitrogen dioxide. Recently, the European Environment Agency (EEA) found that air pollution led to 238,000 premature deaths in the European Union (EU) in 2020.

ESA is launching Sentinel-4 as part of the European Earth Observation Program "Copernicus," which the ESA runs together with the EU in cooperation with the EEA. Over the long term, the data this instrument collects will serve the Copernicus Atmosphere Monitoring Service, which provides continuous data on the composition of the atmosphere over Europe and the rest of the world. The ESA will launch two Sentinel-4 instruments in series to reach a total lifetime of 15 years.

Preserving Healthy Air Quality for All

According to a recent study, most of the world is breathing unsafe air, taking more than two years off of global life expectancy. After the launch of TEMPO and Sentinel-4, the “constellation” of space- based instruments monitoring air pollution across the globe will help us assess the causes, movement, and impacts of air pollution in unprecedented detail. Data collected by these instruments will be made freely available to all scientists who are seeking to understand the dynamics of air quality. The near-real-time data these instruments provide will drastically improve our ability to forecast air quality changes throughout the day and protect the most densely populated areas in the Northern Hemisphere from exposure to harmful pollutants so everyone can ultimately breathe a little easier.