In early 2020, as the COVID-19 pandemic spread around the globe, countries from China to Canada imposed strict lockdowns to slow the spread of the coronavirus. Unfortunately, these restrictions had the unfortunate side-effect of slowing the global economy to a crawl. The ramifications of this economic slowdown were evident in the businesses that closed their doors and the people who lost their jobs. The impact of the COVID-19 lockdowns manifested in less obvious ways too, such as in the decrease of atmospheric pollutants associated with economic activity. For example, a study led by Dr. Kazuyuki Miyazaki at NASA’s Jet Propulsion Laboratory (JPL) found that emissions of nitrogen oxides (NOx), key ingredients in the formation of ozone and a danger to human health, decreased 15 percent globally, with local reductions as high as 50 percent. As a result of the lower NOx emissions, by June 2020, global measurements of atmospheric ozone dropped to a level that policymakers thought would take at least 15 years to reach by conventional means, such as environmental regulation.
To conduct this study, the researchers used measurements of NOx, ozone, and other atmospheric gases from Earth-observing satellites and fed these data into numerical models of atmospheric chemical reactions and weather, using a data analysis and retrieval system developed by JPL’s TRopospheric Ozone and its Precursors from Earth System Sounding (TROPESS) Project.
Tropospheric soundings from Earth observing satellite instruments provide critical information about atmospheric composition and its impact on human health and climate. TROPESS uses these sounding data to generate Earth System Data Records (ESDRs) of ozone and other atmospheric constituents by processing data from multiple satellites through a common retrieval algorithm and ground data system.
TROPESS builds upon the success of the Tropospheric Emission Spectrometer (TES) instrument aboard NASA’s Aura satellite. Launched in 2004, Aura’s mission is to measure trace gases in the atmosphere by detecting their unique spectral signatures. TES was the first instrument designed to monitor ozone in the lowest layers of the atmosphere from space and its high spectral resolution radiance observations led to new measurements of atmospheric gases.
TROPESS project team members are involved in a range of activities, including the analysis, validation, and dissemination of data products produced by the TROPESS Science Data Processing System (SDPS). These data products are intended to provide a continuous record of ozone and other trace-gas species.
“We’re producing a whole suite of products of atmospheric composition, such as carbon monoxide, ozone, methane, water vapor in the atmosphere, by combining radiances from a number of satellite instruments,” said Dr. Kevin W. Bowman, the Project Scientist for the TROPESS project. “The TES team pioneered the combination of these different satellite products to generate enhanced products, particularly by combining data from TES and OMI (the Ozone Monitoring Instrument, aboard NASA’s Aura satellite). TROPESS draws on that lineage, pulls the algorithms that were developed under TES, and now applies them to a wider range of satellite instruments.”
Radiances are measurements of the absorption and scattering of molecules (e.g., water vapor, carbon dioxide, ozone) integrated across different altitudes in the atmosphere. In addition to OMI, TROPESS incorporates measurements from the Cross-track Infrared Sounder (CrIS) aboard the joint NASA/NOAA Suomi National Polar-orbiting Partnership (Suomi NPP) and NOAA-20 satellites, and the Atmospheric Infrared Sounder (AIRS) on NASA's Aqua satellite.
The TROPESS team combines these data from the three hyper-spectral thermal infrared, near-infrared, and ultraviolet atmospheric sounding instruments via a common retrieval framework known as the MUlti-SpEctra, MUlti-SpEcies, Multi-SEnsors (MUSES) science data processing system (MUSES-SDPS) to generate its ESDR data products of Earth’s tropospheric composition.
“We’re using the same algorithm across a suite of Level 1B products and instruments,” said Bowman. “Normally, satellite teams will build a bespoke algorithm for their particular instrument. Then, another team will build an algorithm for their instrument, even if those two instruments are similar. It’s unusual to use the same algorithm, particularly for instruments that measured disparate radiances such as the thermal infrared and ultraviolet.”
The result of this approach is the production of data products with sensitivities superior to measurements derived from any single instrument.
“Imagine you have binoculars and you only looked at objects from the left side or from the right side,” Bowman said. “Well, you can still see the object, and they both tell you something about the scene, but when you put the left and right together, you get a much clearer picture and really start to get a sense of depth.”
TROPESS aims to provide that clarity and depth with an expansive suite of data products offering combined measurements from three satellite instruments—CrIS, AIRS, and OMI—delivered in three modes: the Forward Stream, generated from the MUSES-SDPS; Special Collections, data products produced for specific campaigns; and a Reanalysis Stream.
The TROPESS forward processing stream generates products that include atmospheric composition measurements of ozone (O3), carbon monoxide (CO), ammonia (NH3), peroxyacetyl nitrate (PAN), methane (CH4), and deuterated water vapor (HDO) derived from CrIS, AIRS, and OMI radiances. These products offer global day and nighttime coverage.
As for the Special Collections, there are currently two. The first collection offers data products focused on the 2020 wildfires in California from August through October 2020 and the second offers data products associated with the wildfires in Australia that took place from November 2019 through January 2020. Both collections are derived from CrIS radiances, but the former provides atmospheric composition measurements of ozone (O3), carbon monoxide (CO), ammonia (NH3), and peroxyacetyl nitrate (PAN), while the latter also includes deuterated water vapor (HDO).
TROPESS plans to begin processing the Reanalysis Product, a multidecadal record generated from the MUSES-SDPS, this fall.
According to Bowman, the TROPESS data products will be of interest to anyone engaged in the study of atmospheric chemistry, air quality, or the interplay between atmospheric chemistry and the Earth System.
“TROPESS products span the overall Earth system and allows us to connect them together,” he said. “You can see, for example, that when the fires occur, ammonia is going up, ozone is going up, carbon monoxide is going up, and you can see where they go. The combustion is a single event, but it generates a lot of different pollutants that affect the carbon cycle, water cycle, and nitrogen cycle in addition to atmospheric chemistry. This interaction points to the concept of Earth System Sounding that motivates our approach.”
TROPESS data products are also ideal for ingestion into atmospheric models for chemical weather prediction.
“[These data are] very well suited for forecasting the movement of trace gasses in the atmosphere,” said Bowman. “The response of ozone to COVID-19 lockdowns is transported like temperature, rain, or clouds. It’s chemistry on the move.”
Bowman also expects these data will become useful for international products, such as the Troposphere Ozone Assessment Report, an initiative of the International Global Atmospheric Chemistry Project developed by an international team of more than 200 experts from over 35 countries. The aim of the report is to provide the research community with an up-to-date scientific assessment of tropospheric ozone’s global distribution and trends from the surface to the tropopause (the boundary in the Earth's atmosphere between the troposphere and the stratosphere).
The TROPESS data products are generated using legacy TES data processing algorithms and Level 1B inputs from either a single instrument (e.g., AIRS, CrIS, or OMI) or combinations of multiple instruments (e.g., AIRS-OMI). They are available in NetCDF format, so they can be used with the data visualization tool Panoply and the browsing and editing tool HDFView. The products also include geolocation information, estimated errors, quality flags, and other materials.
TROPESS data products are available from NASA Earthdata Search and the TROPESS project website. The website also provides documentation pertaining to tools users can access for help in extracting data. TROPESS data products are also available from NASA's Goddard Earth Sciences Data and Information Services Center (GES DISC), which manages, archives, and distributes the data, tools, and resources in NASA’s Earth Observing System Data and Information System (EOSDIS) collection that pertain to atmospheric composition, atmospheric dynamics, global precipitation, and solar irradiance. TROPESS data products are not available in the Earthdata Cloud at this time, but they are expected to be in the future.