Atmos. Meas. Tech., 11, 1061–1085, 2018 https://doi.org/10.5194/amt-11-1061-2018 © Author(s) 2018. This work is distributed under the Creative Commons Attribution 4.0 License. The CHRONOS mission: capability for sub-hourly synoptic observations of carbon monoxide and methane to quantify emissions and transport of air pollution David P. Edwards1, Helen M. Worden1, Doreen Neil2, Gene Francis1, Tim Valle3, and Avelino F. Arellano Jr.4 1National Center for Atmospheric Research (NCAR), Boulder, CO, USA 2NASA Langley Research Center, Hampton, VA, USA 3Ball Aerospace, Boulder, CO, USA 4Department of Hydrology and Atmospheric Sciences, University of Arizona, Tucson, AZ, USA Correspondence: David P. Edwards ([email protected]) Received: 15 June 2017 – Discussion started: 28 June 2017 Revised: 21 December 2017 – Accepted: 3 January 2018 – Published: 23 February 2018 Abstract. The CHRONOS space mission concept provides servations would find direct societal applications for air qual- time-resolved abundance for emissions and transport stud- ity management and forecasting to protect public health. ies of the highly variable and highly uncertain air pollu- tants carbon monoxide and methane, with sub-hourly re- visit rate at fine ( ∼ 4 km) horizontal spatial resolution across a North American domain. CHRONOS can provide com- 1 Introduction plete synoptic air pollution maps (“snapshots”) of the con- tinental domain with less than 10 min of observations. This For the end of the current decade, geostationary Earth or- rapid mapping enables visualization of air pollution trans- bit (GEO) satellite missions for atmospheric composition port simultaneously across the entire continent and enables are planned over North America, East Asia and Europe, a sentinel-like capability for monitoring evolving, or unan- with additional missions in formulation or proposed. To- ticipated, air pollution sources in multiple locations at the gether, these present the possibility of a constellation of GEO same time with high temporal resolution. CHRONOS uses a platforms to achieve continuous, time-resolved, high-density compact imaging gas filter correlation radiometer for these observations of continental domains for mapping pollutant observations, with heritage from more than 17 years of sci- sources and variability on diurnal and local scales with near- entific data and algorithm advances by the science teams hemispheric coverage (CEOS, 2011). In addition to NASA’s for the Measurements of Pollution in the Troposphere (MO- TEMPO (Tropospheric Emissions: Monitoring Pollution) PITT) instrument on NASA’s Terra spacecraft in low Earth mission (Zoogman et al., 2017), the ESA/EUMETSAT (Eu- orbit. To achieve continental-scale sub-hourly sampling, the ropean Space Agency/European Organisation for the Ex- CHRONOS mission would be conducted from geostation- ploitation of Meteorological Satellites) Sentinel-4 mission ary orbit, with the instrument hosted on a communications over Europe (GMES-GAS, 2009) and the Korean KARI or meteorological platform. CHRONOS observations would (Korea Aerospace Research Institute) MP-GEOSAT/GEMS contribute to an integrated observing system for atmospheric (Multi-Purpose Geostationary Satellite/Geostationary Envi- composition using surface, suborbital and satellite data with ronment Monitoring Spectrometer) mission over Asia (Lee et atmospheric chemistry models, as defined by the Committee al., 2010) will provide data products for ozone (O3/, nitrogen on Earth Observing Satellites. Addressing the U.S. National dioxide (NO2/, sulfur dioxide (SO2/, formaldehyde (HCHO) Academy’s 2007 decadal survey direction to characterize di- and aerosol optical depth (AOD) several times per day with urnal changes in tropospheric composition, CHRONOS ob- smaller than 10 km × 10 km spatial footprints. While these planned GEO measurements will provide new information Published by Copernicus Publications on behalf of the European Geosciences Union. 1062 D. P. Edwards et al.: The CHRONOS mission on the diurnal evolution of emissions and chemical transfor- significant impact on local air quality and human health at mation of some important pollutants, they are missing obser- locations near the sources and also downwind. Distinguish- vations of methane (CH4/ and carbon monoxide (CO). As ing the relative contributions of local and non-local pollution identified in CEOS (2011), these gases play key roles in at- sources has emerged as a fundamental challenge for air qual- mospheric chemistry, air quality and climate. ity management in the U.S. (NRC, 2004). Because CO has The planned GEO constellation will be further enhanced a medium lifetime (weeks to months), it can be transported by current and upcoming low Earth orbit (LEO) mis- globally, but it does not become evenly mixed in the tropo- sions with atmospheric composition measurement capability. sphere. This moderate lifetime makes CO an ideal tracer of These missions include OMI (Ozone Monitoring Instrument; combustion-related air pollution (e.g., Edwards et al., 2004, Levelt et al., 2006); IASI (Infrared Atmospheric Sounding 2006). Interferometer; Clerbaux et al., 2009); CrIS (Cross-track In- The CHRONOS mission is motivated by these fundamen- frared Sounder; Gambacorta et al., 2014); OMPS (Ozone tal questions regarding the emissions and transport of air Mapping Profiler Suite; Flynn et al., 2014); and the ESA pollutants. The CHRONOS gas filter correlation radiometry Sentinel-5 precursor mission, TROPOspheric Monitoring In- (GFCR) measurement technique for multispectral CO builds strument (TROPOMI; Veefkind et al., 2012). The LEO as- on 17 years of observations from the NASA Terra satellite sets allow for a transfer standard between the GEO mis- Measurements of Pollution in the Troposphere (MOPITT) sions, filling gaps in the spatial coverage, enabling cross- instrument (Drummond et al., 2010; H. M. Worden et al., calibration and validation and, potentially, combined data 2013), in addition to experience in LEO column CH4 re- products. Such an integrated global observing system for at- trievals from SCIAMACHY (SCanning Imaging Absorption mospheric composition is key to abatement strategies for air SpectroMeter for Atmospheric CHartographY; Frankenberg quality as prescribed in international protocols and conven- et al., 2005, 2011) and GOSAT (Greenhouse Gases Observ- tions (e.g., IGACO, 2004). ing Satellite; Morino et al., 2011; Schepers et al., 2012). Pollution affecting air quality is a complex mixture of The CHRONOS temporal resolution (sub-hourly) and spa- many compounds that was designated a Group 1 carcino- tial resolution (nominally 4 km × 4 km at the domain center) gen by the World Health Organization (WHO) (Loomis et are required to capture the near-surface trace gas variabil- al., 2013) amidst rising concerns about increased mortality ity, as concluded by modeling and data studies performed by and economic costs. Outdoor air pollution causes pulmonary the Geostationary Coastal and Air Pollution Events (GEO- and cardiovascular diseases, lung cancer and premature birth CAPE) (Fishman et al., 2012) science team in response to (Brunekreef and Holgate, 2002; M. C. Turner et al., 2015; the first decadal survey for Earth Science and Applications Fann et al., 2012, Malley et al., 2017). Despite improvements from Space (NRC, 2007). For CH4, the spatially and tem- in U.S. air quality in recent decades, present-day levels of air porally dense CHRONOS measurements over the entire con- pollution are estimated to decrease average life expectancy tinental U.S. measurement domain would address the need by 0.7 years and contribute to 10 % of the total deaths in for consistent assessments of CH4 emissions at decision- highly polluted areas such as Los Angeles (Fann et al., 2012). relevant scales. For CO, proven multispectral retrieval tech- In 2010, over 3 % of U.S. preterm births were attributed to niques (Worden et al., 2010) increase the information on CO air pollution at an estimated cost exceeding USD 5 billion vertical distribution and can identify vertical transport from (Trasande et al., 2016). To address the causes of air pollu- one observation to the next. Thus, CHRONOS is capable of tion effectively, decision makers need comprehensive mea- tracking pollutants from the surface, where they are emitted, surements to quantify the full suite of pollutants, including to where they degrade downwind air quality. CH4 and CO, emitted from industrial, transport and energy This paper describes the CHRONOS science, measure- sectors, as well as natural sources. CO, which allows detec- ment technique, expected performance (precision and accu- tion of combustion-related emissions, serves as the reference racy), retrieval vertical sensitivity and observing strategy. We for the emissions of many difficult-to-measure pollutants that then show how CHRONOS would complement observations impact air quality and climate. Wildfires, which emit both from other current and planned satellite instruments, and we CO and CH4, are a particular concern in the western U.S. conclude with a summary of CHRONOS features and advan- (Abatzoglou and Williams, 2016), where burn areas have in- tages. creased by a factor of 6 since 1970, with severe economic impacts (Westerling et al., 2006). CO and CH4 emissions also have significant consequences for climate change, es- 2 CHRONOS science pecially considering CH4 pollution due to recent large in- creases in natural gas production (Pétron et al., 2012; Miller 2.1 CHRONOS sub-hourly synoptic measurements et al., 2013)