**2. Analyzed Objects**

We analyzed emissions from the two main combined heat and power plants in the city of Lodz (Figure 1). Lodz is the third largest city in Poland (Central Europe) in terms of the number of inhabitants (area: 293.2 km2; population density: 2292.2 people/km2; population: 672,185). In the north-west part of the city, there is a combined heat and power plant designated with the number EC-3 (Figure 2A). This combustion installation includes five coal-fired steam boilers, including one capable of co-firing 20% biomass with hard coal, one steam boiler fired with light fuel oil, and three water boilers fired with heavy oil. The total thermal power is 804 MW, and the electric power is 205.85 MW. To the north and west of EC-3 there are industrial areas, and to the east and south there are single-family and multi-family residential areas. The gross development index in the area ranges from 0.5 to 1.0.

**Figure 1.** Location of the EC-3 and EC-4 CHP plants in the city of Lodz in Poland, Europe (photo background source: Google Earth Pro).

**Figure 2.** Location and immediate surroundings of the heat and power plant EC-3 (**A**) and EC-4 (**B**) (photo background source: Google Earth Pro).

The second facility is the EC-4 CHP plant in the east of the city (Figure 2B). The EC-4 fuel combustion installation includes two coal-fired steam boilers, one biomass-fired steam boiler, one light fuel oil-fired steam boiler, and three coal-fired water boilers. The total thermal power of EC-4 is 820 MW, and its electric power output is 198 MW. In the immediate vicinity of EC-4 is an industrial and storage district. However, to the north and north-west nearby, there are single-family housing and collective housing areas. Towards the south, there are industrial areas, and towards the east and north-east, there are recreational and leisure areas with high greenery in the form of trees. The gross development index in this area ranges from 0.5 to 1.0. Significant sources of pollution in close proximity to both heat and power plants include busy roads leading to housing estates and out of the city. These line sources contribute to increasing the level of pollution in the area.
