Assessing High-Resolution NO2 Retrievals from EMIT over the Middle East

Abstract

Nitrogen dioxide (NO2) is a key pollutant in the troposphere that alters atmospheric composition and poses a significant risk to human health. Therefore, continuous monitoring of NO2 is essential for air quality assessment and environmental decision making.

Satellite observations of NO2 have advanced substantially over the past three decades, with major developments from early missions such as GOME to current sensors like TROPOMI. In addition, geostationary missions including GEMS, TEMPO, and Sentinel-4 now provide hourly observations, enabling detailed analyses of temporal variability. While these advances have improved the monitoring of localized emissions and regional pollution patterns, the achievable spatial resolution remains limited to the kilometer scale.

Recently, low spectral resolution hyperspectral imagers with bandwidths of about 5 to 10 nm have emerged, offering contiguous spectral coverage combined with meter-scale spatial sampling. Although primarily designed for surface applications, these instruments have demonstrated potential for trace gas retrievals, including NO2, as shown for the EnMAP mission (e.g., Borger et al., 2025). However, EnMAP's sparse spatial coverage limits its applicability for broader, systematic analyses.

An instrument with similar characteristics to EnMAP is the Earth Surface Mineral Dust Source Investigation (EMIT) mission. Installed aboard the International Space Station, EMIT provides continuous global coverage and repeated observations with a ground pixel size of 60 x 60 m2.

Here, we build on the previous EnMAP study and assess the potential of NO2 retrievals from EMIT. For our investigations, we select the Middle East, where observation conditions are favorable due to high surface albedo and strong emission sources. In particular, we focus on megacities, many of which act as so-called "area sources" and are located in coastal regions. Both cases pose distinct challenges, with current spatial resolution often limiting detailed emission monitoring and source localization.

References: Borger et al.: High-resolution observations of NO2 and CO2 emission plumes from EnMAP satellite measurements, Environ. Res. Lett., 20, 044034, https://doi.org/10.1088/1748-9326/adc0b1, 2025.