Two Air Quality Regimes in Total Column NO2 Over the Gulf of Mexico in May 2019: Shipboard and Satellite Views.

The Satellite Coastal and Oceanic Atmospheric Pollution Experiment (SCOAPE) cruise in the Gulf of Mexico was conducted in May 2019 by NASA and the Bureau of Ocean Energy Management to determine the feasibility of using satellite data to measure air quality in a region of concentrated oil and natural gas (ONG) operations. SCOAPE addressed both technological and scientific issues related to measuring NO2 columns over the outer continental shelf. Featured were nitrogen dioxide (NO2) instruments (Pandora, Teledyne API analyzer) at Cocodrie, LA (29.26°, −90.66°), and on the Research Vessel Point Sur operating off the Louisiana coast with measurements of ozone, carbon monoxide, and volatile organic compounds (VOCs). The findings: (a) all NO2 observations revealed two atmospheric regimes over the Gulf, the first influenced by tropical air in 10–14 May, the second influenced by flow from urban areas on 15–17 May; (b) comparisons of OMI v4 and TROPOMI v1.3 TC (total column) NO2 data with shipboard Pandora NO2 column observations averaged 13% agreement with the largest difference during 15–17 May (∼20%). At Cocodrie, the satellite–Pandora agreement was ∼5%. (c) Three new‐model Pandora instruments displayed a TC NO2 precision of 0.01 Dobson Units (∼5%); (d) regions of smaller, older natural gas operations showed high methane readings from leakage; elevated VOCs were also detected. Neither satellite nor spectrometer captured the magnitude of ambient NO2 variability near ONG platforms. Given an absence of regular air quality monitoring over the Gulf of Mexico, SCOAPE data constitute a baseline against which future observations can be compared. Plain Language Summary: The Satellite Coastal and Oceanic Atmospheric Pollution Experiment (SCOAPE) cruise in the Gulf of Mexico (GOM) conducted on the Research Vessel Point Sur in May 2019 investigated the feasibility of using satellite data to measure air quality in a region of concentrated oil and natural gas (ONG) operations. SCOAPE addressed both technological and scientific issues related to measuring NO2 columns in a prototypical coastal environment. The results are as follows. First, measurements from SCOAPE demonstrated that satellite NO2 data can be used to monitor ONG activity over the GOM. Second, during SCOAPE both OMI and TROPOMI TC (total column) NO2 amounts were higher over land and sometimes the near‐shore ONG‐rich Gulf, than over deepwater regions farther offshore. This was confirmed by Pandora spectrometer "ground truth" TC NO2 data measured throughout SCOAPE on shore and on ship. Third, SCOAPE established the reliability and precision of a new generation of Pandora spectrometers. Fourth, comparisons of satellite and Pandora TC NO2 data in SCOAPE confirm previous land–water interface studies that point to limitations in satellite NO2 in coastal regions. Finally, neither satellite nor spectrometer captures the magnitude of ambient ("nose‐level") NO2 variability in a region dotted with hundreds of ONG platforms. Key Points: Shipboard Pandora NO2 columns and surface O3, NO2, CO, and volatile organic compounds (VOCs) over the Gulf of Mexico (GOM), May 2019, displayed two air quality (AQ) regimesGOM AQ was dominated by continental NO2 sources and near‐shore VOC; deepwater oil platforms were in a clean marine regimePandora and satellite total column NO2 over GOM agreed overall within 5% in clean, clear‐sky conditions along the coast and 13% over water [ABSTRACT FROM AUTHOR]