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Principal Investigator (PI): Lok Lamsal, Universities Space Research Association, Columbia, MD

Nitrogen oxides (NOx=NO+NO2), produced during combustion processes, are designated as criteria pollutants by the U.S. Environmental Protection Agency (EPA) due to their negative effects on public health and the environment. They are precursors of ozone and particulate matter, both of which are also criteria pollutants that have important implications for air quality, crop yields, and climate. While several space-based instruments have made NO2 observations over the past 20+ years, the satellite-based NO2 datasets have rarely been analyzed together in a systematic way due to algorithmic, instrumental, and observational differences.

We are developing consistent long-term global data records of tropospheric and stratospheric NO2 columns as well as value-added surface NO2 concentrations and anthropogenic NOx emissions. We will achieve this by applying our mature NO2 algorithms developed for the NASA Earth Observing System (EOS) Aura Ozone Monitoring Instrument (OMI) to similar satellite spectrometers including heritage, concurrent, and upcoming instruments that observe at different times of day.

Over the past 12 years, our NASA OMI Science team has developed, implemented, and maintained the official NASA OMI NO2 product. Our OMI NO2 product, archived at the NASA Goddard Earth Sciences Data and Information Services Center (GES DISC), has been widely used to quantify tropospheric pollution levels, study decadal world-wide changes in NO2, evaluate chemical transport models, infer NOx emissions, and study NOx chemistry and lifetime. OMI NO2 is one of the most widely utilized Aura datasets with over 400 research articles. The paper describing our version 2 NO2 data set (A new stratospheric and tropospheric NO2 retrieval algorithm for nadir-viewing satellite instruments: applications to OMI, Bucsela et al., 2013) is the second most downloaded paper in the history of the journal Atmospheric Measurement Techniques. The number of users, science applications, and publications from these data continues to grow.

Objective 1
Adapt OMI operational algorithms to other satellite instruments and create and archive consistent multi-satellite Level 2 and Level 3 NO2 products. We will adapt our well-validated OMI NO2, cloud, and geometry-dependent surface reflectivity retrieval algorithms to prior and contemporaneous satellite instruments that include Global Ozone Monitoring Experiment (GOME), 1996-2003; SCanning Imaging Absorption spectroMeter for Atmospheric CHartographY (SCIAMACHY), 2002-2012; Global Ozone Monitoring Experiment 2 (GOME-2), 2007-present; and TROPOspheric Monitoring Instrument (TROPOMI), launched September 2017. The proposed adaptation of the OMI Level 2 algorithms to these instruments will provide a self-consistent, long-term records ideally suited for analysis of global trends, diurnal changes in NO2 columns, and NOx emissions.

Objective 2
Evaluate data sets developed in Objective 1 for consistency. We will assess multi-satellite data from Objective 1 using independent observations from ground-based and in-situ sensors, and characterize multi-satellite consistency, accounting for changes in satellite footprint sizes and NO2 diurnal cycles. We will conduct multi-sensor, cross-calibration analyses by

  1. Determining vicarious calibration adjustment factors,
  2. systematically evaluating the temporal stability of the satellite spectrometers, and
  3. assessing the accuracy of derived products and their consistency.

Objective 3
Generate and archive higher level (Level 4) products. Using the outcomes from Objectives 1 and 2 and recent advances in NASA’s modeling capabilities, we will generate Level 4 products to enable new science and applied projects: surface NO2 concentrations and NOx emissions.

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