*3.3. Total Average Number and Mass Concentrations of Particulate Matter in Wroclaw and Cracow*

The final stage of the analysis of the results of the studies carried out in Wroclaw and Cracow consisted in creating the characteristics presenting the total average concentration of particulate matter in terms of number and mass with a division into air pollution sources. The results obtained are shown in Figure 5a,b.

**Figure 5.** Total average concentration of particle number (**a**) and particulate mass (**b**) in each city (in red line marked alarm level for PM10 emission settled by Inspectorate of Environmental Protection).

Figure 5a presents an analysis of the total average number concentration (CPN) of particulate matter obtained during air quality measurements in Wroclaw and Cracow. Data were divided according to the type of source of measured immission (transport, household and point). The results obtained for individual sources were as follows:


Figure 5b presents an analysis of the total average mass concentration (CPM) of particulate matter obtained during air quality measurements in Wroclaw and Cracow. Data were divided according to the type of source of measured immission (point, household and transport). The results obtained for individual sources were as follows:


Figure 5b presents a total average mass concentration of particulate matter obtained during measurements at 1 September 2020 in Wroclaw and 3 September 2020 in Cracow. Equipment, which was used to measurements has range to 10.00 μm. This mean that prepared graph shows concentration of particulate matter to 10.00 μm (PM10). The red line in Figure 5b indicates the limit above which the smog alarm is announced.

In order to compare, the results of measurements taken on the same day by the measuring station of the Environmental Protection Inspectorate were checked. The differences

between the results from the Environmental Protection Inspectorate and those obtained during the research result from the location of the research stations. The measurements carried out by the authors were focused on points with increased emissions. Therefore, the measurements showed a large exceedance of PM10 standards and indicate the regionalization of the city's pollution. During the measurements hours, the PM10 results obtained by the Inspectorate of Environmental Protection did not exceed 40 μg/m3 for Wroclaw and 50 μg/m<sup>3</sup> for Cracow. The data was obtained from the measurement data bank of the Environmental Protection Inspectorate for the selected station located in the vicinity of the measurement points identified in the research. Figure 6a,b show the averaged results of the performed measurements. The value of the immission obtained from transport was set as the baseline. Thanks to this, the percentage differences obtained in other sectors were determined. The obtained results were also presented in terms of low and high (point) imission. Low imission is the sum of the values obtained for the transport and household sectors (Figure 7a,b).

**Figure 6.** Total average concentration of particles distribution in terms of: (**a**) number, (**b**) mass.

**Figure 7.** Low and high particle emission results in terms of: (**a**) number, (**b**) mass.

#### **4. Discussion**

The area of interest during testing was particles up to 10.00 μm in aerodynamic diameter. At each of the measurement points, both morning and afternoon particulate matter occurred over the entire measurement range. Due to the number distribution, small diameter particles (up to 0.3 μm) predominated during the tests. The largest number of particles was in the size range up to 1 μm. In the case of Wroclaw, there was a significant difference between the number of particles obtained during the morning measurement compared to the afternoon one. The weather conditions were considered the cause. Rainfall

accompanied all morning measurements in Wroclaw. Moreover, it intensified with each subsequent measurement. A relation between the degree of rainfall intensity and the accompanying wind with increased PM immission was noticed. During the rainfall, a very large number of solid particles were observed, in terms of mass and number. The authors of the study [26,27] mention the influence of humidity on air quality. In effect, that morning rain was effective in reducing the particulate immission, i.e., cleaning the air. In Cracow, on the other hand, the values obtained during the morning and afternoon measurements were similar.

The predominant share of particles with a diameter smaller than 1 μm (almost 100%) was observed during the measurements. This means that it is these smallest particles that are most abundant in the air. This effect is visible in both the Wroclaw and Cracow agglomerations. It is worth noting that the point-source measurement is also nearby a highway as well as a nearby railway station where the emissions from the train and diesel engine locomotive are present not only household exhaust emissions. Wind and wind turbulences which mix the particulate matter around the city and country also exist. The conducted assessment of pollution with particles pays particular attention to the share of the smallest particle size (up to 1 micrometer) in the total emissions. It is these particles that are not filtered by the human body and go directly into the respiratory system.

In terms of mass distribution, particles with a diameter greater than 1.5 μm represented the largest shares in the mass of particles. According to the obtained mass distributions of particulate matter within Wroclaw and Cracow agglomerations, the particles with a larger diameter, i.e., about 5 μm, have the greatest impact on the particulate matter immissions. The share of particulate matter with a diameter smaller than 1 μm is significantly decreased compared to the numerical distribution. This means that both in Cracow and Wroclaw (from the perspective of mass distribution of particulate matter) particles with larger diameters dominate.

The results in Figure 7 show that the transport sector is not at all the largest source of the measured particulate pollution immission in all cases. Due to the number of particles, it would be better to take a closer look at transport in Cracow. The obtained data show that the imission from households and the point imission are about 40% lower. On the other hand, in Wroclaw the biggest problem (during the research) was the point imissions. Due to the mass of particles, transport is the main source of air pollution with particles. It follows from the results obtained by us that the main source of PM pollution is low emission (surface and transport). Industrial chimneys, responsible mainly for point emission, are high, therefore the pollution is dispersed over a much larger area, far beyond the city limits.

Figure 5 presents the results of the particulate matters up to 10 μm. According to the legislation, these are PM10. The results obtained during the measurements were compared with the data from official sources of Environmental Protection Inspectorate. As expected, the obtained results not only significantly exceeded the values presented by the Environmental Protection Inspectorate, but also the daily PM10 standards (in some cases, even by twice). This means that despite meeting the legal requirements, it would be worth considering a more precise location of the measuring stations.

The results obtained indicate that it is necessary to improve measurement methods, especially for the smallest particles, smaller than PM2.5. As mentioned in the Introduction the number of measuring stations, not only in Wroclaw and Cracow but also across Poland, is insufficient. This also applies to the measurement of particles smaller than 2.5 μm. Our measurements were not made in accordance with the guidelines of Environmental Protection Inspectorate, however indicated that it is necessary to extend the measurements performed by the smallest particles. The assessment thus carried out highlights the shortcomings of air quality monitoring stations measuring these smallest particles. Perhaps the application of the method [28], but extended by the measurement of particulate matter, would help in determining better measuring station locations. The choice of the location of the measurement points in our research was not accidental. Similarly to [6], we were guided not only by the data from official reports, but also by taking into account subjective

factors that are not taken into account in the analyses of the Environmental Protection Inspectorate. Unfortunately, both of these cities struggle with the problem of poor air quality and nuisance smog. It is related not only to the location of both cities, but also to the habits of the inhabitants. Coal stoves are still used as the main source of heating in many homes. Fortunately, the situation is improving year by year. City authorities introduce new restrictions and activate programs aimed at achieving clean air such as replacement of stoves, development of bicycle infrastructure, restrictions on vehicle entry to city centers. This applies both to subsidies encouraging residents to use green energy, and to changing the city's infrastructure.

#### **5. Conclusions**

Nowadays, air pollution is considered to be one of the biggest problems affecting society worldwide [29–32]. Specific attention is paid to one component of pollution, i.e., excessive particulate emissions. This is a crucial contaminant since it contains other pollutants adsorbed on particle surfaces, such as heavy metals. Unfortunately, Poland is at the top of the European countries with the worst air quality. Particle immission tests were carried out in two Polish cities (Wroclaw and Cracow). A total of 12 tests were carried out during the measurements (two for each type of immission source). Each measurement location represented one type of emission: transport, household and point. The conducted research shows that it is the low immission, i.e., from transport and households, that is the largest source of air pollution in the locations selected by us. The results obtained during the measurements clearly indicate that the data are not consistent with those presented by the Environmental Protection Inspectorate. The data analyzed in this article is much larger, and additionally significantly exceeds the daily PM10 standard. Despite the fact that the Environmental Protection Inspectorate's measuring stations are arranged in accordance with legal requirements, they are still insufficiently precise. There are still places, popular on the map of Wroclaw and Cracow, where excessive PM10 emissions occur, despite satisfactory data from official sources.

Moreover, the measurements performed by the Inspectorate of Environmental Protection are not sufficient. It should be necessary to expand research to include monitoring of particulate matter PM1 and even smaller ones. The next step should be to perform further, more detailed research. On that basis, it will be possible to propose a new method for selecting the location of measurement points, especially in those places where excessive particulate emissions are a problem. Obviously, this will not directly improve air quality, but it will certainly enable better monitoring. This will enable local improvements to be made, which in the long run will have a positive impact on air quality throughout the city. Additionally, in order to reduce the level of pollution in the studied cities, it is suggested to develop social programs aimed at actively acting against air pollution. In addition, the city authorities in their environmental protection programs should focus on replacing furnaces, changing road infrastructure, expanding bicycle paths, or introducing various benefits for people using electric motor vehicles.

**Author Contributions:** Conceptualization, R.J. and M.G.-G.; methodology, R.J.; software, M.N.; validation, P.K., M.M., M.G. and K.K.; formal analysis, K.K.; investigation, P.K.; resources, M.M.; data curation, M.N.; writing—original draft preparation, K.K. and M.M.; writing—review and editing, K.K. and M.M.; visualization, M.M., K.K. and P.K.; supervision, M.G.-G.; project administration, R.J.; funding acquisition, R.J. All authors have read and agreed to the published version of the manuscript.

**Funding:** This research and APC was funded by Interdisciplinary Rector's Grant, grant number 559 ERP/33/32/SIGR/0004.

**Institutional Review Board Statement:** Not applicable.

**Informed Consent Statement:** Not applicable.

**Data Availability Statement:** Data available on request due to restriction e.g., privacy or ethical. The data presented in this study are available on request from the corresponding author. The data are not publicly available due to ongoing project.

**Conflicts of Interest:** The authors declare no conflict of interest.
