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High concentration levels of air pollutants may cause damage to plants, animals, and the health of some groups of human beings. Therefore, it is important to investigate different topics related to the high air pollution levels and to find reliable answers to the questions about the possible damages, which might take place when these levels exceed some limits. A few of the numerous questions, the answers of which are highly desirable, are listed below: (a) When are the air pollution levels dangerous? (b) What is the reason for the increased air pollution levels? (c) How can the air pollution levels be decreased? (d) Will the future climate changes result in higher and more dangerous air pollution levels? It is necessary to study carefully many issues connected with the distribution of air pollutants in a given region and with the reasons for the increases of the concentrations to high levels, which might be damaging. In order to do this, it is necessary to develop a Digital Twin of all relevant physical processes in the atmosphere and to use after that this tool in different applications. Such a tool, its name is DIGITAL AIR, has been created. Digital Twins are becoming more and more popular). Many complex problems, arising taking place in very complicated surroundings, can be handled and resolved successfully by applying Digital Twins. The preparation of such a digital tool as well as its practical implementation in the treatment of a special problem, the increase of some potentially dangerous ozone levels, will be discussed and tested in this paper. The Unified Danish Eulerian Model (UNI-DEM) is a very important part of DIGITAL AIR. This mathematical model, UNI-DEM, can be applied in many different studies related to damaging effects caused by high air pollution levels. We shall use it in this paper to get a reliable answer to a very special but extremely important question: will the future climatic changes lead to an increase in the ozone pollution levels in Bulgaria and Europe, which can potentially become dangerous for human health? [ABSTRACT FROM AUTHOR]

Lightning is one of the leading causes of weather-related fatalities worldwide and also has a strong impact on atmospheric chemistry (i.e., NOx production). Lightning can also lead to power system breakdowns, ignite forest fires, damage wind turbine and lead to perturbation of transportation, in particular to aviation. Thus, knowing when, where lightning strike and which atmospheric environments are more frequently associated with lightning is important. Furthermore, given the increase in the population density in recent decades (i.e., more people are exposed to lightning) and the increased urbanization (i.e., cities are getting larger and thus are more exposed to lightning) is essential to understand the spatial and temporal distribution of storm producing lightning and their environments in the current climate and their changes in the past and coming decades. To address these issues, in this study we analyze the changes in the number of days with atmospheric conditions leading to lightning over southeastern Europe. Here we consider the non-inductive charging mechanism as the main mechanism for cloud electrification. We search for ingredients supporting for this cloud electrification mechanism using a series of parameters (e.g., convective available potential energy, total precipitable water, heights of various isotherms) obtained from vertical profiles collected from radiosonde sites over southeastern Europe (e.g., Romania, Hungary, Bulgaria). This paper will present the changes between 1980 and 2018 in the number of days with condition supporting the occurrence of lightning in urban areas from southeastern Europe. [ABSTRACT FROM AUTHOR]