## 1 Introduction
During the last period, many articles discussed the pollution level in Romania ([PERSON] et al., 2016; [PERSON] et al., 2016; [PERSON] et al., 2016; [PERSON] et al., 2016; [PERSON] et al., 2016; [PERSON] et al., 2016; [PERSON] et al., 2016). However, only a few addressed the pollution in urban or industrial zones ([PERSON] et al., 2002; [PERSON] et al., 2016; [PERSON] et al., 2016). The present study aims to evaluate the degree of pollution with VOCs in the area of an oil refinery in the northern part of the Romanian Litttoral. As explained in the following section, the study area's strategic importance, added to by the presence of hazardous substances regulated by Romanian Law No. 59/2016, emphasizes the relevance of understanding emissions in this context. The research offers important insights into VOC emissions in a refinery during maintenance in the context of the environmental implications and impact on the workers and people living in the Navodari and Mamaia cities and neighboring villages. An extended statistical analysis of 41 series of pollutants recorded in three zones of the storage tanks during a maintenance period (one month) is performed. The series' correlation and similarities are assessed to understand the series characteristics, which are the basis of grouping the observation sites into clusters. Considering ten statistical futures, the series from each zone are clustered using the k-means algorithm. We show that this procedure allows a more effective assignation of each series in the groups than when using the raw data series for the same purpose. Its advantage lies in its adaptability to various case studies. It emphasizes that knowledge of some basic statistics allows a fast analysis of the pollution level during a specific period, providing valuable insights and information. Our search of the statistical literature did not return results on similar attempts. Moreover, our study aligns with or advances current trends in air quality management in industrial settings by:  
* _Involvement of VOCs in Global Environmental Challenges._ VOC emissions contribute significantly to the formation of tropospheric ozone and other particles present in the atmosphere, affecting human health and ecosystems. Our study makes an important contribution by highlighting emissions from a critical operational phase--the verification period for high-volatility petroleum storage tanks--which is often overlooked in environmental reports. * _Alignment with the General International/National Regulatory Framework._ The analysis of atmospheric pollutant concentrations with respect to the EU and Romania's standards is based on measurements taken at fixed sampling points. Our research provides an analytical framework adapted to meet the requirements of European, national, and local regulations. Since emission/immision monitoring differs by parameters of interest, the limit concentrations, and observation frequencies, the regulations in the field are different. The reference documents taken into account, which present the codes and regulations required in the design of both petroleum storage tanks under atmospheric pressure and those under pressure are the Decision (EU) 2017/1757 of the Council of 17 July 2017, regarding the acceptance, on behalf of the European Union, of an amendment to the 1999 Protocol to the 1979 Convention on Long-Range Transboundary Air Pollution to reduce the degree of acidification, eutrophication, and the level of tropospheric ozone [29] and Law no. 264 of 20 December 2017, regarding the establishment of technical requirements to limit emissions of volatile organic compounds (VOCs) resulting from gasoline storage and distribution from terminals to gas stations, as well as during vehicle refueling at gas stations [30]. Identifying critical areas and classifying data series based on their statistical characteristics facilitates decision-making for compliance and pollution reduction in industrial areas.