Satellite Monitoring of Nitrogen Dioxide: From Retrieval Uncertainties to Emission Sources

Satellite observations of NO2 offer daily global coverage of air quality that ground-based networks cannot achieve. Instruments such as the Ozone Monitoring Instrument (OMI) and the Global Ozone Monitoring Experiment-2 (GOME-2) have collected multi-decadal records essential for detecting atmospheric composition trends. However, retrieval uncertainties — from spectral fitting, stratosphere-troposphere separation, and air mass factor computation — can obscure real emission changes and weaken policy assessments. This thesis investigates such uncertainties by evaluating spectral fitting algorithms from the EU's QA4ECV project, intercomparing OMI and GOME-2A NO2 and formaldehyde retrievals, and refining corrections for stratospheric contributions, air mass factors, and temperature dependencies. Applying these improved retrievals reveals striking NO2 declines over the Netherlands with concurrent rising ozone, signalling chemical regime shifts. Over China, combining OMI NO2 and SO2 observations enables classification of emission source types and their spatiotemporal redistribution. Now extended by TROPOMI, these long-term records establish satellite NO2 as an essential tool for monitoring emissions, evaluating air-quality policies, and tracking Earth's changing atmosphere from space.