TEMPO (Tropospheric Emissions: Monitoring of Pollution)
TEMPO is a spaceborne instrument mission which was selected in November 2012 through NASA’s first EVI (Earth Venture Instrument) solicitation. NASA's EVI is part of the agency’s ESSP (Earth System Science Pathfinder) program. The goal of the TEMPO mission is to monitor major air pollutants from geostationary orbit across the North American continent hourly during daytime. The competitively selected TEMPO proposal is led by Kelly Chance of SAO (Smithsonian Astrophysical Observatory), Cambridge, MA, USA. The instrument will be developed at BATC (Ball Aerospace and Technologies Corporation), the project management is provided by NASA/LaRC. Other collaborative institutions are: NASA/GSFC, NOAA, EPA, NCAR, Harvard, UC Berkeley, St. Louis University, University of Alabama, Huntsville, and the University of Nebraska. International collaboration is provided by KARI and NIER (Korea), ESA (European Space Agency), and Canada. 1) 2) 3) 4)
As PI (Principal Investigator), Kelly Chance is responsible for developing an instrument that will measure major air pollutants over Greater North America, from Mexico City to the Canadian tar sands, and from the Atlantic to the Pacific, every daylight hour. The measurements will be taken from geostationary orbit, which will enable continuous data collection over this region. A unique aspect of this mission is that the instrument will be a hosted payload flown on a commercial geostationary satellite. TEMPO will be the North American geostationary component of an international constellation for air quality monitoring. 5) 6)
The TEMPO mission builds on the science team’s experience with the European GOME (Global Ozone Monitoring Experiment) and SCIAMACHY (Scanning Imaging Absorption Spectrometer for Atmospheric Cartography) missions and with the OMI (Ozone Monitoring Instrument) flying on NASA’s Aura spacecraft. All of these missions measure atmospheric pollution from a sun-synchronous polar orbit. If the projected 2018-2019 launch timeframe holds for TEMPO, its observations should coincide with measurements from Europe’s Sentinel-4 mission, planned for launch in 2019, and Korea’s MP-GEOSat (Multi-Purpose Geostationary Satellite), planned for launch in 2018. The Sentinel-4 mission will consist of an UVNS (Ultraviolet-Visible-Near-Infrared Spectrometer), a sounder accommodated on MTG-S (Meteosat Third Generation Sounder) platforms of EUMETSAT. All three missions will have similar geostationary orbits and similar air quality observation objectives. The three satellites will comprise a constellation for observing continental air quality and estimating transcontinental transport of pollu-tion across the Atlantic and Pacific oceans. 7)
Table 1: Overview of sun-synchronous nadir heritage instruments
Table 2: Alignment with 2007 Decadal Survey
The TEMPO science objectives result from many years of experience with requirements developed by the air quality community, using observations of pollution from sun-synchronous, polar orbits. TEMPO’s advanced capabilities over heritage instruments are designed to answer the following science questions:
1) What are the temporal and spatial variations of emissions of gases and aerosols important for air quality and climate?
2) How do physical, chemical, and dynamical processes determine tropospheric composition and air quality over spatial scales ranging from urban to continental, and temporally from diurnal to seasonal?
3) How does air pollution drive climate forcing, and how does climate change affect air quality on a continental scale?
4) How can observations from space improve air quality forecasts and assessments for societal benefit?
5) How does intercontinental pollution transport affect air quality?
6) How do episodic events (e.g., wild fires, dust outbreaks, and volcanic eruptions) affect atmospheric composition and air quality?
Each of these questions has been explored from polar orbit using data from OMI onboard Aura of NASA, SCIAMACHY on the Envisat mission of ESA, and the GOME instruments flown on EUMETSAT missions. These instruments have surveyed key atmospheric constituents that relate to air pollution and quality and include tropospheric and stratospheric ozone (O3), which in the troposphere is a pollutant and a greenhouse gas; sulfur dioxide (SO2); formaldehyde (H2CO); nitrogen dioxide (NO2); glyoxal (C2H2O2); water vapor; cloud properties; aerosol characteristics, including AOD (Aerosol Optical Depth); and UV-B radiation. TEMPO will also measure the same atmospheric constituents, but from geostationary orbit, thereby allowing better spatial and temporal resolutions.
The heritage satellite data have revealed how air quality changes from day-to-day and year-to-year. They have shown improvements in air quality over North America because of regulation of power plant and automobile emissions, and also have tracked recent severe pollution events originating over urban locations from Asia to North America. These observations have more recently shown the degradation of air quality with high amounts of pollution over the Canadian tar-sand oil excavation fields. An example of NO2 data collected from OMI over the course of a year is shown in Figure 1. These data show urban and industrial hot spots that typically result from auto emissions and power plants.
Figure 1: OMI tropospheric NO2 data (1015 molecules cm-2) collected in 2010 of North America (image credit: NASA)
Instrument concept and mission capabilities:
TEMPO is an imaging Offner grating spectrometer measuring solar backscattered Earth radiance. The design will incorporate many of the features and lessons learned from heritage spectrometers flown by Europe and the U.S. The key instrument characteristics and capabilities are:
• Spectral range: 290–690 nm (UV, VIS); spectral sampling: 0.2 nm; spectral resolution: 0.6 nm. A 2D detector (2 k x 2 k pixels) images the full spectral range for each geospatial scene.
• Spatial resolution: 2 km/pixel in the north-south direction, 4.5 km /pixel in the east-west direction at the center of the FOR (Field of Regard) — 36.5° N, 100° W. Co-add/cloud clear as needed for specific data products.
• Hourly measurements stepping east to west of the entire FOR (2.5 x 106 spectra/hour).
• Standard data products and sampling rates:
- NO2, O3, aerosol, and cloud products sampled hourly, including eXceL O3 for selected target areas
- H2CO, C2H2O2, SO2 sampled 3 times/day (hourly samples averaged to get S/N)
- Product spatial resolution ≤ 8 km N/S x 4.5 km E/W at center of domain
- Signal/noise requirements met at SZA (Solar Zenith Angles) less than 50° for all products—and at angles up to 70° for NO2, clouds, and aerosols.
- Ozone profile products include 0–2 km O3, free tropospheric O3, and the stratospheric O3 column.
TEMPO measurements will capture the high variability in the diurnal cycle of emissions and their evolving chemistry, which occurs mostly during the day. TEMPO’s footprint — smaller than for previous missions measuring air quality — will resolve pollution sources at suburban scales. With both high temporal and spatial resolution, TEMPO data will improve emission inventories, monitor population exposure to pollution, and make possible effective emission control strategies by regulatory agencies.
An example of the TEMPO temporal capability is shown in Figure 2. The figure depicts a CMAQ (Community Multi-scale Air Quality) model calculation of column amounts of NO2 over the course of two days based on emissions, photochemistry, and the local meteorology. Two observations from OMI over the same location are also indicated, illustrating the limitations of a polar-orbiting satellite for observing evolving time-of-day processes. The TEMPO observational period shown will be similar to the model calculations, but limited to daytime and cloud-free scenes. TEMPO’s near-continuous observations will be superior to polar orbiting satellite data for verifying model predictions and likely observe features not seen in the model. It is also anticipated that data in the boundary layer will be significantly improved with TEMPO’s higher spatial resolution, which is made possible by longer integration times from geostationary orbit.
Figure 2: Hourly NO2 surface concentration and integrated column calculated by CMAQ air quality model: Houston, TX, June 22-23, 2005 (image credit: TEMPO collaboration)
The mission’s key capabilities are:
• Geostationary location at 100° W longitude—proposed to cover Greater North America.
• Planned data latency is two hours (near real-time) for air quality products developed with the EPA and NOAA.
• A two-year operations (Phase-E) period, driven by the cost cap. The instrument life-time — allowing extended operations — is much greater.
TEMPO will observe the components of pollution and their source gases over all major cities and industrial areas in Greater North America. EPA (Environmental Protection Agency) has designated O3, SO2, NO2, and aerosols as criteria pollutants, and are recognized to be harmful to health and the environment and cause property damage. Major proxies for air pollution include formaldehyde and glyoxal in the atmosphere, indicating the presence of non-methane volatile organic compounds (NMVOC) emissions. The short lifetime of NMVOCs make them ideal for locating the source of emissions from natural and anthropogenic processes, including biomass burning. Figure 3 illustrates the TEMPO instrument’s FOR for a one-hour measurement cycle.
Figure 3: Illustration of the TEMPO instrument’s FOR for a one-hour measurement cycle (image credit: BATC)
Legend to Figure 3: TEMPO’s FOR is outlined in green. The spread with increasing latitude is due to the projection of the FOR as seen from a geostationary orbit where the satellite is over the equator. The narrow white band is an exaggeration of TEMPO’s field of view,nominally 4.5 km, which scans from east to west over the course of an hour. The coverage from south to north will include the range from Mexico City to the Canadian tar sands.
Launch: A launch of TEMPO is planned for 2018. NASA will arrange launch and hosting services.
Orbit: Geostationary orbit, altitude of 35,786 km, an equatorial spacecraft location of 90-110º W is preferred, 80-120º W acceptable.
TEMPO is a low risk mission with significant space heritage:
• All proposed TEMPO measurements have been made from LEO (Low Earth Orbit) satellite instruments to the required precisions
- NASA TOMS-type O3
- SO2, NO2, H2CO, C2H2O2 from AMF (Air Mass Factor)-normalized cross sections
- Absorbing Aerosol Index, UV aerosol, Rotational Raman scattering cloud, UV index eXceL profile O3 for selected geographic targets.
A single geostationary satellite views only one sector of the globe, limiting the capability to observe sources of pollution outside the instrument FOR. Fortunately, both Korea and Europe (ESA and Eumetsat) plan to develop and launch their own instruments to fly on geostationary satellites to measure air composition and quality in the 2017-2022 timeframe. These missions will have measurement capabilities and science objectives similar to TEMPO. Therefore, it will be possible, with a minimum of three geostationary satellites positioned to view Europe, East Asia, and North America, to collectively provide near-global coverage in the Northern Hemisphere. The synergy of contemporaneous satellite missions having similar observing capabilities and data distribution protocols will provide unique opportunities to advance understanding of the interactions between regional and global atmospheric composition in the troposphere. This would include assessments — not possible before — of emission sources, intercontinental pollution trans-port, and regional interactions between air quality and climate. These activities would address several societal benefit areas of GEOSS (Global Earth Observation System of Systems).
In addition to TEMPO, the European Sentinel-4 and the Korean MP-GEOSat missions have been approved. By harmonizing these missions it is possible to improve the scientific return and societal benefit of each of the individual missions while beginning a global observing system that will be impossible for any one country to implement alone. Best efforts to cooperate on defining common requirements and data products can enable improved designs for all instruments and allow cost savings by minimizing duplication of effort. While recognizing that unique requirements likely exist for individual missions, this approach defines common objectives that build a foundation for a future integrated observing system for atmospheric composition, as envisioned in 2004 by the IGOS (Integrated Global Observing System).
Figure 4: The potential global coverage of the three geostationary missions, separated by roughly 120º in longitude (image credit: J. Ziemke, GSFC, and the OMI and MLS instrument and algorithm teams)
Legend to Figure 4: The 3 images show simulation of average tropospheric ozone — an indicator of poor air quality — using data from Aura’s OMI and MLS (Microwave Limb Sounder) when viewed from three geostationary positions over major continents for May-July 2008. The three geostationary missions (i.e., originated by NASA, ESA, and Korea) however, will focus on the Northern Hemisphere only. Shades of purple and blue correspond to 10-20 DU (Dobson Units), representing low ozone amounts, while lighter shades correspond to 35-50 DU. Green, yellow, and red indicate high-pollution areas.
The simultaneous development of these individual missions to acquire data over Earth’s major industrialized regions presents a real opportunity for international collaboration to improve the preparation for these missions and their combined capabilities within a global system. Best efforts are all ready underway to cooperate on defining common measurement requirements, retrieval algorithms, validation, data quality, and access to achieve the above goals. Consistency of data products will result in better understanding of the science, improved application capabilities, and subsequent use by regulatory agencies.
1) Steve Cole, “New Space Sensor as a Hosted Payload to Track Air Pollution Across North America,” NASA Release: 12-390, Nov. 08,2012, URL: http://www.nasa.gov/home/hqnews/2012/nov/HQ_12-390_TEMPO_Instrument.html
2) “Langley-Led Project to Build Space-Based Pollution Monitor, NASA/LaRC, Nov. 19, 2012, URL: http://www.nasa.gov/centers/langley/science/TEMPO.html
3) “Ball Aerospace Selected by NASA for TEMPO Air Pollution Mission,” BATC, Nov. 19, 2013, URL: http://www.ballaerospace.com/page.jsp?page=30&id=501
4) Andrea Martin, “TEMPO, the Recently-Selected Earth Venture Instrument for Daytime Pollution Monitoring, Enabled by Key Early Technology Investments,” NASA, Dec. 2012, URL: http://esto.nasa.gov/news/news_TEMPO_12_2012.html
5) Kelly Chance, Brad, Pierce, “TEMPO, keeping the beat with Air Quality, Tropospheric Emissions: Monitoring of Pollution,” CIMSS Science Symposium, Madison, Wisconsin, USA, Dec. 12, 2012, URL: http://www.google.de/url?sa=t&rct=j&q=tempo%20(tropospheric%20emissions%3A%20monitoring%20of%20pollution)
6) Kelly Chance & the TEMPO Team“Tropospheric Emissions: Monitoring of Pollution (TEMPO)”, April 6, 2013, URL: http://www.google.de/url?sa=t&rct=j&q=tempo%20(tropospheric%20emissions%3A%20monitoring%20of%20pollution)
7) Ernest Hilsenrath, “NASA Ups the TEMPO on Monitoring Air Pollution,” The Earth Observer Newsletter, Harvard-Smithsonian Center for Astrophysics, March-April 2013, Volume 25, Issue 2, URL: http://www.google.de/url?sa=t&rct=j&q=geo-cape%2C%20tempo&source=web&cd=4&cad=rja&sqi=2&ved=0CEsQFjAD&
The information compiled and edited in this article was provided by Herbert J. Kramer from his documentation of: ”Observation of the Earth and Its Environment: Survey of Missions and Sensors” (Springer Verlag) as well as many other sources after the publication of the 4th edition in 2002. - Comments and corrections to this article are always welcome for further updates.