Tropospheric emissions: Monitoring of pollution (TEMPO)

Highlights

• TEMPO is under development to collect geostationary air quality measurements.

• TEMPO will measure every hour during daylight over greater North America.

• TEMPO will have the spatial resolution to measure sub-urban variability.

• The mission’s primary data products include tropospheric ozone and related species.

• TEMPO’s time-resolved observations form a revolutionary data set for air quality.

Abstract

TEMPO was selected in 2012 by NASA as the first Earth Venture Instrument, for launch between 2018 and 2021. It will measure atmospheric pollution for greater North America from space using ultraviolet and visible spectroscopy. TEMPO observes from Mexico City, Cuba, and the Bahamas to the Canadian oil sands, and from the Atlantic to the Pacific, hourly and at high spatial resolution (~2.1 km N/S×4.4 km E/W at 36.5°N, 100°W). TEMPO provides a tropospheric measurement suite that includes the key elements of tropospheric air pollution chemistry, as well as contributing to carbon cycle knowledge. Measurements are made hourly from geostationary (GEO) orbit, to capture the high variability present in the diurnal cycle of emissions and chemistry that are unobservable from current low-Earth orbit (LEO) satellites that measure once per day. The small product spatial footprint resolves pollution sources at sub-urban scale. Together, this temporal and spatial resolution improves emission inventories, monitors population exposure, and enables effective emission-control strategies.

TEMPO takes advantage of a commercial GEO host spacecraft to provide a modest cost mission that measures the spectra required to retrieve ozone (O₃), nitrogen dioxide (NO₂), sulfur dioxide (SO₂), formaldehyde (H₂CO), glyoxal (C₂H₂O₂), bromine monoxide (BrO), IO (iodine monoxide), water vapor, aerosols, cloud parameters, ultraviolet radiation, and foliage properties. TEMPO thus measures the major elements, directly or by proxy, in the tropospheric O₃ chemistry cycle. Multi-spectral observations provide sensitivity to O₃ in the lowermost troposphere, substantially reducing uncertainty in air quality predictions. TEMPO quantifies and tracks the evolution of aerosol loading. It provides these near-real-time air quality products that will be made publicly available. TEMPO will launch at a prime time to be the North American component of the global geostationary constellation of pollution monitoring together with the European Sentinel-4 (S4) and Korean Geostationary Environment Monitoring Spectrometer (GEMS) instruments.

Introduction

Over the past decades, observation of the atmospheric species from space has become an increasingly powerful tool for understanding the processes that govern atmospheric composition and air quality. However, while past and present satellite measurements provide global coverage, their coarse spatial and temporal sampling preclude answering many of the current questions relevant to air quality concerning emissions, variability, and episodic events. Conversely, the in situ measurements from surface sites that are currently used for air quality monitoring have limited spatial density and coverage. The Tropospheric Emissions: Monitoring of Pollution (TEMPO) geostationary (GEO) mission is planned to address many of the shortcomings of the current atmospheric composition observing system.

The TEMPO instrument will be delivered in 2017 for integration onto the nadir deck of a NASA-selected GEO host spacecraft for launch as early as 2018. TEMPO and its Asian (GEMS) and European (Sentinel-4) constellation partners make the first tropospheric trace gas measurements from GEO, building on the heritage of six spectrometers flown in low-Earth orbit (LEO). These LEO instruments measure the needed spectra, although at coarser spatial and temporal resolutions, to the precisions required for TEMPO. They use retrieval algorithms developed for them by TEMPO Science Team members and that are currently running in operational environments. This makes TEMPO an innovative use of a well-proven technique, able to produce a revolutionary data set.

The 2007 National Research Council (NRC) Decadal Survey “Earth Science and Applications from Space” included the recommendation for the Geostationary Coastal and Air Pollution Events (GEO-CAPE) mission to launch in 2013–2016 to advance the science of both coastal ocean biophysics and atmospheric-pollution chemistry [78]. While GEO-CAPE is not planned for implementation this decade, TEMPO will provide much of the atmospheric measurement capability recommended for GEO-CAPE. Instruments from Europe (Sentinel 4) and Asia (GEMS) will form parts of a global GEO constellation for pollution monitoring within several years, with a major focus on intercontinental pollution transport. Concurrent LEO instruments will observe pollution over oceans [125], which will then be observed by these GEO instruments once they enter each field of regard [130]. TEMPO will launch at a prime time to be a component of this constellation, and is also a pathfinder for the hosted payload mission strategy.

Section 2 outlines the TEMPO mission and provides the historical and scientific background for the mission. Section 3 describes the instrument specifications, design, and expected performance. 4 TEMPO implementation, 5 TEMPO operations give a brief overview of TEMPO implementation and operations, respectively. Section 6 describes TEMPO in the context of a global GEO constellation and international partnerships in North America. Section 7 outlines the trace gas, aerosol, and other science products TEMPO produces along with detailing the state-of-the-science ozone profile retrievals TEMPO performs. Section 8 describes the validation efforts that are part of the TEMPO mission. Section 9 details the various science studies that are enabled by TEMPO. Section 10 outlines the public outreach and education opportunities that we are pursuing related to TEMPO.