**1. Introduction**

The monitoring and evaluation of ambient air quality is the first important step in controlling air pollution. Monitoring pollutant concentrations in air is pivotal to properly manage air quality [1,2]. Air pollution can be defined as a phenomenon harmful to the ecological system and the normal conditions of human existence and development when some substances in the atmosphere exceed a certain concentration [3]. Air pollution comes from a wide variety of sources, which discharge of harmful substances into the atmosphere, causing adverse effects to humans and the environment. They can be natural or anthropogenic [4]. One of harmful pollutants are particulate matters. Fine particulate matters of aerodynamic diameter lower than 2.5 μm (PM2.5) are considered to be one of the most important environmental factors contributing to the global human disease burden [5]. As half of the world's population (55%) lives in urban areas, the environmental degradation produced by cities threatens the health and quality of life of a fair share of the world's population [6]. Many articles focus on explaining the connections between pollutants and their toxicological effects on the environment [7]. Outdoor air pollution led to an estimated 4.2 million premature deaths worldwide and half a million in the European Union (EU) in 2016 [8,9]. Exposure to ambient PM2.5 particulate matter has been found to be associated with different negative health endpoints, from minor respiratory symptoms to premature mortality. This worldwide burden of disease includes 7–10 million premature deaths, mostly in developing countries [10]. Acute lower respiratory infections (ALRI), including pneumonia and bronchiolitis of bacterial and viral origin, are the largest single cause of mortality among young children worldwide and thus account for a significant burden of disease worldwide [11]. Outdoor air pollution has been associated with increased symptoms and increased ALRI mortality.

**Citation:** Jasi ´nski, R.; Galant-Goł ˛ebiewska, M.; Nowak, M.; Ginter, M.; Kurzawska, P.; Kurtyka, K.; Maciejewska, M. Case Study of Pollution with Particulate Matter in Selected Locations of Polish Cities. *Energies* **2021**, *14*, 2529. https:// doi.org/10.3390/en14092529

Academic Editor: T. M. Indra Mahlia

Received: 31 March 2021 Accepted: 25 April 2021 Published: 28 April 2021

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Toxicologic evidence suggests that exposure to particulate air pollution can cause pulmonary inflammation and affect host defenses against infection [12]. The World Health Organization (WHO) estimated, that in 2016, 91% of the world population was living in places where the WHO air quality guidelines levels were not met. According to WHO, about 440,000 people die every year due to air pollution in Europe. In Poland only, which is at the forefront of European countries with the most polluted air, it is about 44,000 people a year [8]. Based on the specificity of formation and the influence of particles on the human body it can be stated that one of the basic issues in assessing air quality is the concentration of particles. Particulate matter is a term generally used to describe a type of air pollutant consisting of a complex of various mixtures of suspended particles that vary in size, composition and place of formation [13]. The main sources of this type of pollution are factories, power plants, incinerators, motor vehicles and many others. The basic division of particles is based on their aerodynamic diameter, which allows for the determination of two main groups: PM2.5 and PM10, i.e., particulate matter with diameters smaller than 2.5 μm and 10 μm, respectively [14].

Air quality monitoring is carried out in Poland by the Environmental Protection Inspectorate. On the basis of the reports and their analyses, it was concluded that the air in Poland is one of the most polluted in Europe. In 2018, the WHO published a list [15] of the 50 most polluted cities in Europe. Unfortunately, Poland is at the top of this list. In terms of PM2.5 as many as 36 of those cities are located in Poland. One of them is Cracow, which is the subject of this article's analysis. As mentioned, the assessment of air quality in Poland is carried out by the Inspectorate of Environmental Protection. Measurement stations and measurement methods are established in accordance with the relevant Regulations of the Environment Ministry.

On problem is the insufficient number of measuring stations in Poland and the fact that only a small part of them measures PM2.5 particles and none of them measures particles up to 1 micrometer in diameter (e.g., in the city of Poznan there are five measuring stations, and only three of them allow the measurement of both PM10 and PM2.5). The ambient air pollution is particularly noticeable in urban agglomerations, but unfortunately it is not limited to them. The deterioration of air quality is already observable in much smaller towns and even villages. In the case of the developing countries, the problem is more serious due to overpopulation and uncontrolled urbanization along with the development of industrialization [16]. The author of [17] pointed out that in Poland the particularly negative impact on air quality is related to households and transport. The transport sector is being developed in the direction of electromobility, however, Polish roads are still dominated by vehicles equipped with conventional engines. Recent scientific studies [18–20], carried out in Poland, analyse the impact of particulate emissions from both road and air transport. The authors of [19] have made an analysis to classify the vehicles and also to identify the advantages of the latest developments in conventional, hybrid and electric vehicles.

The aim of the article was the assessment of particulate air pollution in two selected cities in Poland. Firstly, the particle emission sources were identified in selected locations in two Polish cities (Wroclaw and Cracow), and then measurement of particles in terms of their mass distribution and numbers was performed.
