Detailed mapping of NO₂ pollution sources with the TROPOMI instrument operated in zoom-mode

Abstract

Anthropogenic nitrogen dioxide (NO₂) in the troposphere is mainly produced by combustion engines in traffic, industry and energy production, and continues to affect air quality, human health and environment. Daily global measurements of tropospheric NO₂ columns are obtained by satellites with increasing spatial resolution and signal-to-noise levels, to improve monitoring of emission sources and air quality forecasting. The recently launched TROPOMI instrument on-board ESA’s Sentinel-5 Precursor satellite measures tropospheric NO₂ with a spatial resolution of 7.1 km by 3.6 km. During its commissioning phase, the instrument was temporarily operated in ’zoom-mode’ to measure at a resolution of 2.4 km by 1.8 km. This research presents the processed results from this unique data-set, which allows mapping NO₂ pollution sources from space with unprecedented detail. Comparison to measurements at operational resolution shows the improvement in spatial information content, at the cost of increased noise and uncertainty. The benefits and possibilities of measuring tropospheric NO₂ at high resolution are explored with several case studies. Comparisons with chemical transfer model forecasts show the improved ability of these measurements to capture local NO₂ enhancements and possibly improve emission inventories. The found correlations with co-located space-borne CO₂ column observations and the performance of a plume detection algorithm applied to the data-set provide additional support for simultaneous high resolution measurements of co-emitted CO₂ and NO₂, planned for future satellites to improve CO₂ emission monitoring. Finally, test retrievals with the zoom-mode data, using experimental high resolution surface reflectivity and NO₂ profile shape input, demonstrate the potential impact of high resolution a priori databases on the retrieval performance.