## 1 Introduction
A recent study [24] utilized TROPOMI and MODIS satellite data to analyze the spatial distribution and temporal variation of aerosol optical depth (AOD) over eastern China, with a specific focus on the impacts of the COVID-19 lockdown. The research highlights significant reductions in AOD during the lockdown period, driven by decreased human activities, alongside seasonal variations influenced by meteorological conditions. These findings underscore the potential benefits of reducing pollutant emissions on a global scale and highlight the need for sustainable practices to mitigate the adverse effects of air pollution on human health and the environment [25; 26]. Overall, the pandemic served as a valuable case study, emphasizing the importance of understanding the anthropogenic influence on air quality and the effectiveness of emission reduction strategies [27]. This study aimed to capitalize on the unique opportunity presented by the COVID-19 pandemic to analyze the impact of anti-spread measures on PM\({}_{10}\) pollution levels during the lockdown. The research covered the period from 1 January 2017 to 31 December 2022, which includes both periods of regular commercial, traffic, and industrial activity (2017-2019 and 2021-2022), as well as the pandemic year of 2020 [28]. The results were analyzed in the context of the traffic restriction policies put in place by the government during the pandemic year of 2020. To date, no study in Romania has conducted a comparative analysis of PM\({}_{10}\) levels across the three largest cities, which are targeted by the European Commission's air quality infringement procedure, while specifically comparing the pandemic year 2020 [29]. This study sought to fill this gap in the literature, providing valuable insights into the relationship between the pandemic, air pollution, and human health within the Romanian context. Additionally, this study aimed to investigate the elevated PM\({}_{10}\) levels detected during the lockdown on 27 March 2020. Building on the insights gained from the COVID-19 lockdown's impact on air quality, it is important to address the broader challenges faced by countries with less experience in air pollution monitoring, particularly in Eastern Europe. In contrast to Western European nations, Romania began systematic air quality monitoring relatively late, only after the fall of the Iron Curtain. The national air quality monitoring network was established in Bucharest in late 2004 and gradually expanded across the country. Despite these efforts, Romania, like other countries such as Croatia and Ireland, has struggled to fully align with EU Directives and WHO guidelines on air quality within a short timeframe [30]. While Romania's legislation now mirrors EU air quality policy, the practical implementation has been less successful. [PERSON] (2021) provides an in-depth discussion of the various factors contributing to Romania's lag in adopting the EU acquis on air quality [31]. A significant challenge has been the limited experience in developing monitoring capacity, leading to outdated infrastructure, gaps in data series, limited information about the chemical composition of particulate matter, and insufficient funding for the maintenance and operation of monitoring devices, including human resources. These issues have frequently resulted in Romania facing infringement procedures from the European Commission for exceeding permissible levels of particulate matter and nitrogen oxides. The cities of Bucharest, Brasov, and Iasi are among the most polluted in Romania and are under scrutiny by the European Commission due to their high levels of PM\({}_{10}\) pollution. This context underscores the importance of the present study, which not only addresses the immediate impacts of the COVID-19 lockdown on air quality but also offers insights that may be valuable for other countries facing similar challenges in air quality management and compliance. This article is structured as follows.