**1. Introduction**

According to data from the European Commission's Joint Research Center (JRS) [1], as much as 75% of the world's population lives in urban agglomerations. In Europe, the urbanization rate was 72% in 2015 [1]. Therefore, the state of air quality in large urban agglomerations is a matter of key concern. According to a European Environment Agency (EEA) report from 2020 [2], the most frequently analyzed pollutants are PM10, PM2.5, and SO2. This is because large populations are exposed to these pollutants at concentrations higher than recommended by the EU and WHO. According to an EEA report [2], as much as 48% of the population living in urban agglomerations is exposed to concentrations of PM10 above the acceptable level of 20 μg/m3 (average annual concentration) set by the WHO in 2005 [3], and 15% of the urban population in Europe is exposed to concentrations of PM10 above the EU standard of 40 μg/m3 (average annual concentration of PM10) [4]. Moreover, 74% of the urban population is exposed to average annual concentrations of PM2.5 above the permissible level of 10 μg/m3 established by the WHO, and 19% of people are exposed to an average daily concentration of SO2 above the recommended limit of 20 μg/m3. Using less restrictive EU standards, only 4% of the European population is exposed to levels of PM2.5 beyond the permissible concentration of 25 μg/m<sup>3</sup> and less than 1% of the European

**Citation:** Cichowicz, R.; Dobrza ´nski, M. Analysis of Air Pollution around a CHP Plant: Real Measurements vs. Computer Simulations. *Energies* **2022**, *15*, 553. https://doi.org/10.3390/ en15020553

Academic Editors: Francesco Nocera and Robert H. Beach

Received: 25 November 2021 Accepted: 10 January 2022 Published: 13 January 2022

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population is exposed to SO2 at levels above the recommended limit of 125 μg/m3 (24-h limit). However, in 2021, the WHO [5] updated its statements regarding permissible levels of pollutants. For PM10 and PM2.5, the permissible annual average concentrations were reduced by 25% and 50%, respectively, to 15 μg/m3 and 5 μg/m3. In the case of SO2, the permissible level was increased by 100% from 20 μg/m3 to 40 μg/m<sup>3</sup> (average daily SO2 concentration), but this is still well below the limit permitted by the EU.

The main emitters of pollutants are the energy industry [6,7], agriculture, individual heating systems [8], and road transport [9,10]. According to the EEA [2], 41% of PM10 emissions are produced by secondary energy consumers (the commercial and public sectors, as well as private households), 10% by road transport, and 3% by the energy industry. The energy industry is responsible for as much as 47% of the emissions of gaseous pollutants, including SO2. Other industries are responsible for 33% of gaseous pollutants, while households together with the service sector and trade sector contribute 15%. This information is based on statistical data collected by air quality monitoring systems situated in all European Union member states and varies between nations. The monitoring system consists of stationary ground stations that measure pollutant concentrations in a manual daily system and an automatic continuous system [11]. Due to the low density of air quality monitoring stations, the data they collect cannot be used for a detailed analysis of the impact of individual pollution sources on local air quality. For example, in Poland there are about 0.00062 stations/km2 (in 2017, the number of PM10 measurement stations was 194). In Europe overall, the figure is about 0.00060 stations/km2 (there were 2551 PM10 measurement stations in 2017) [12]. For this reason, air quality tests carried out with mobile measurement devices [13] or using numerical programs for calculating/simulating pollutant dispersion in a selected local area are very important. Mobile measuring equipment, such as unmanned aerial vehicles, can be used to transport measuring devices [14,15] or small stationary devices [16]. Numerical programs available include Aero 2010, Emitor, OPA03 [17], AERMOD [18], ENVI-met, and Austal 2000 [19,20].

In this study, we analyzed various anthropogenic sources of pollutants in a selected area, using numerical calculations and real measurements.

#### **2. Methodology**

### *2.1. Analyzed Area*

The analysis was focused on an urban area in the city of Łód ´z. Łód ´z is the third largest city in Poland (central-eastern Europe) in terms of the number of inhabitants (population density: 2292.2 people/km2, population: 672,185, area: 293.2 km2). The area comprises a thoroughfare running from the west to the east along Pojezierska Street, on the intersection between Aleja Włókniarzy and Zgierska Street (Figure 1).

Figure 2 shows the selected fragment of the street (no. 1) is about 1.5 km long and runs through areas of different types and purposes. We distinguish between shopping areas with large-area stores (no. 2), green areas and parks (no. 3), single-family housing areas (no. 4), multi-family developments (no. 5) and industrial areas (no. 6). The gross development index in the area ranges from 0.5 to 1.0. The analyzed street plays an important role as a road transport route connecting two main streets in the city in the east–west system. It is both a local access route to residential and industrial areas and a transit route through the city. According to [21], the average traffic volume on this road section for every 15 min is between 500 and 750 vehicles (between 2000 and 3000 vehicles per hour). In the close vicinity, there is one of the two main heat and power plants in the city, called EC-3 (Figure 2). The EC-3 combustion installation includes 9 boilers: five coal-fired steam boilers, one steam boiler fired with light fuel oil, and three water boilers fired with heavy oil. The total thermal capacity is 804 MW, and the electrical capacity is 205.85 MW [22].

**Figure 1.** Location of the research area in the city of Łód´z in Poland, Europe (photo background source: Google Earth Pro).
