Ambient air pollution, with consequences to the environment, human health and climate change, affects regions around the world. However, with the lockdown imposed during the COVID-19 epidemic, reductions in nitrogen dioxide (NO2) concentrations - one of the main urban pollutants - have been reported in many parts of the world, by 70% and 80% in Barcelona region, 64% in other cities in Spain, about 40% in London and New York, and about 60% in New Delhi region. In this context, the present paper shows the results of monitoring NO2 concentrations within the INCERC Bucharest Branch, located in the eastern part of Bucharest, Romania. Monitoring of NO2 concentrations was performed in three stages: the period before the state of emergency (February-March 2020), during the first month (March-April 2020) and the second month of it (April-May 2020). The model HAZ-SCANNER EPAS, manufacturer SKC - United Kingdom, was the equipment used for monitoring ambient air quality, acquired under the project PN 19 33 04 02 - Sustainable solutions to ensure the health and safety of the population in concept of open innovation and environmental protection. The monitoring method consists in the qualitative and quantitative identification of the inorganic compound NO2 using the electrochemical principle and the recording continuously of its concentrations, at interval of 1 minute. The experimental average values of NO2 concentration, obtained before the state of emergency, was of 36.1ppb, with a minimum of 11.6ppb and a maximum of 57.9ppb. In the first month of the state of emergency, it was of 13.6ppb, with a minimum of 3.0ppb and a maximum of 28.7ppb. Meanwhile, in the second month, the average was of 15.5ppb, with a minimum of 4.7ppb and a maximum of 41.7ppb. The analysis of the above-mentioned values of NO2 concentrations indicated a decrease in the NO2 concentration during the two months of the state of emergency, both of the minimum values recorded and of the maximum and average values, the decrease of the average values being of 62.3%, in the first month and of 57.0%, in the second. The outcomes on declining concentrations of one of the major external pollutants may seem positive, but air quality remains an issue that requires long-term attention from communities, as air pollution affects million people worldwide each year. The conclusion is clear: it is possible to implement major interventions in cities for health reasons, as well as changing priorities so that maintaining clean ambient air becomes a key concern.