## 2 Materials and Methods  
### Emission Data for Scenarios  
Emission reductions due to potential interventions in each scenario were based on an analysis of the Energy Efficiency in Poland Report (EE) created by the Polish Institute of Environmental Economics [23]. This report consists of various publicly available data in Poland, and, additionally, it consists of a national survey based on a representative group providing unique data on the shares of boiler types in households. The first part of the information was about the share of heating boilers types. There is currently no obligation or system for recording the number of solid fuel-fired boilers in Poland. Therefore, data from the survey were the only available information at the time of analysis. Since the lowest quality solid-fuel boilers were analyzed in Scenarios 1 and 2, data on wood or coal boilers were used. The majority of solid-fuel boilers used in households are highly emitting, approximately 81.5%, which was the number used for Scenarios 1 and 2. Data on the emission per boiler were used to calculate the potential reduction. Data from the national study were used to take into account the solid fuel characteristics in Poland [24]. Emission per unit of energy was used (g/GJ), as shown in Table 1.  
Scenarios 1 and 2 assume that hard coal of the lowest quality was replaced. The EE provides additional information about the age of the boiler; taking this into account, boiler emission was set to 420 g/GJ, new units were assumed to be a mix of automatic and manual with 100 g/GJ, and gas was set to 0.5 g/GJ. Since particulate emission from burning gas \begin{table}
\begin{tabular}{c c c c c c c} \hline \hline \multirow{2}{*}{**Pollutant**} & \multirow{2}{*}{**Unit**} & \multicolumn{4}{c}{**Hard Coal**} & \multicolumn{2}{c}{**Other Fuels**} \\ \cline{3-6}  & & **Manual Boilers,** & **Manual Boilers,** & **Automatic** & **Stove** & **Gas** & **Oil** \\ \hline PM\({}_{10}\) & g/GJ & 460 & 130 & 70 & 450 & 0.5 & 3 \\ PM\({}_{2.5}\) & g/GJ & 448 & 121 & 61 & 448 & 0.5 & 2.7 \\ \hline \hline \end{tabular}
\end{table} 
Table 1: Particulate emission factors for household boilers used for Scenarios 1 and 2.  
compared to coal and biomass is negligible, we assumed that whole household PM\({}_{10}\) and PM\({}_{2.5}\) come from solid fuels. Therefore, for Scenario 1, 81.5% of manual boilers of low quality with emission of 420 g/GJ were upgraded to gas 0.5 g/GJ, and for Scenario 2 to new high-quality boilers with 100 g/GJ. Scenario 3 concerned the thermal refurbishment of households. For insulation data, the age of the building was selected. The assumption was that the houses were built according to the existing standards and materials available at the time of building. The age of buildings was collected from the Polish census of 2011 [25]. Data on energy consumption were taken from the EE, which is based on the energy standards in each period. Detailed information is presented in Tables 2 and 3. The differences between the two regions are due to destruction during World War II. Data come from the Polish census of 2011 and are the latest available with regional distribution. The thermal refurbishment scenario used an energy consumption per household of 45 kWh/m\({}^{2}\) annually, which represents a low-energy building. It was assumed that households in buildings dating from before 1944 and during 1945-1988 need better insulation. A limitation of this approach is that it does not consider the existing refurbishment of houses. Since this information does not exist in Poland, it could not be included. Emission reduction results produce a flat spatial difference, due to a lack of local data. Therefore, there is a single percentage reduction value for each scenario per region. However, the contribution of household emission is different in each cell of the grid used in the air quality modeling. Therefore, the same emission percentage reduction produces different concentration percentage reductions.