Of the nitrogen oxides, NO2 has the greatest impact on humans. The areas with its highest concentrations within the EU are these most populated and industrialised ones. Excessive nitrogen dioxide concentrations are responsible for around 75,000 premature deaths of EU residents each year; in Poland, this value reaches almost 1,900. Since 2017, there have been new possibilities to measure NO2 concentration, made as part of the Copernicus Sentinels-5P Programme. Hence, it is purposeful to analyse changes in nitrogen dioxide emissions in the most important Polish cities against the EU in spring and summer 2020. The basis for the analysis was satellite data collected during the Copernicus Sentinels-5P Programme. In 2020, there were huge changes in NO2 concentration, which were the consequences of the implementation of restrictive safety measures relating to the COVID-19 pandemic: a significant reduction in road traffic and the closure or limiting of production in many industrial plants. It was found that, as a result of lockdown, nitrogen dioxide concentrations in Poland's largest cities fell to a much lesser degree than in cities of similar size in southern or western Europe. The analyses indicated that data obtained from the Copernicus Sentinel-5P satellite will play a key role in monitoring changes in nitrogen dioxide concentration throughout the EU. Ground-based observations of nitrogen dioxide concentrations, which have dominated until recently, will remain only of comparative importance in the assessment and analysis of the compound concentration.

26.4.2021