## 3 Results
### Variation in Air Quality in Tourist Reception Areas  
The mean annual concentrations for all national parks were changing from 28.4 \(\upmu\)mol/m\({}^{2}\) (2020) to 30.1 \(\upmu\)mol/m\({}^{2}\) (2021) in the period under study. In three parks, it exceeded 40 \(\upmu\)mol/m\({}^{2}\). The following national parks had the greatest NO\({}_{2}\) content in the air (in 2021): Kampinowski (48 \(\upmu\)mol/m\({}^{2}\)), Ojcowski (46 \(\upmu\)mol/m\({}^{2}\)), Ujscie Warty (41 \(\upmu\)mol/m\({}^{2}\)), \begin{table}
\begin{tabular}{c c c c c c} \hline \hline
**Month** & **Mean** & **Median** &
\begin{tabular}{c} **Standard** \\ **Deviation** \\ \end{tabular} & **VC [\%]** & **Maximum** \\ \hline January & 39.48 & 32.56 & 30.21 & 76.5 & 383.55 \\ February & 56.46 & 56.86 & 16.80 & 29.7 & 145.42 \\ March & 37.03 & 35.95 & 12.68 & 34.3 & 126.86 \\ April & 33.26 & 31.86 & 9.61 & 28.9 & 105.33 \\ May & 27.54 & 26.53 & 7.89 & 28.7 & 94.76 \\ June & 25.45 & 24.89 & 5.05 & 19.9 & 78.36 \\ July & 24.05 & 23.52 & 6.63 & 27.5 & 88.46 \\ August & 27.40 & 26.68 & 6.71 & 24.5 & 83.60 \\ September & 31.92 & 31.01 & 7.59 & 23.8 & 74.45 \\ October & 48.57 & 48.34 & 11.46 & 23.6 & 130.77 \\ November & 50.34 & 49.21 & 13.85 & 27.5 & 115.29 \\ December & 55.08 & 54.39 & 17.10 & 31.0 & 132.39 \\ \hline \hline \end{tabular}
\end{table} 
Table 1: Monthly variation in nitrogen dioxide concentrations over Poland in 2019 [\(\upmu\)mol/m\({}^{2}\)]. Figure 4: Mean annual NO\({}_{2}\) concentrations by type of tourist reception area for 2019–2021: A—national parks, B—landscape parks, C—tourist regions, D—health resorts, and E—provincial capitals. Wielkopolski (40 umol/m\({}^{2}\)), and Swietokrzyski (37 umol/m\({}^{2}\)). The best quality of the air occurred in the following national parks: Bieszczakoki (18 umol/m\({}^{2}\)), Tatrzanski (23 umol/m\({}^{2}\)), Babiogorski (24 umol/m\({}^{2}\)), Wigierski (24 umol/m\({}^{2}\)), and Slowinski (24 umol/m\({}^{2}\)). The trends for 2019 and 2020 are the same, but the values are slightly lower. Compared to 2020, the greatest increase in mean values in 2021 occurred in the following national parks: Bory Tucholskie (22%), Kampinowski (18%), Gor Stolowe (16%), Ojcowski (15%), and Swietokrzyski NP (12%). The greatest decrease in NO\({}_{2}\) concentration occurred in Poleski (7%), Roztoczanski (7%), and Wielkopolski (2%) national parks. When comparing the 2021 data with the data for 2019, the decreases for these national parks range from 8 to 16%, with the biggest being in Wielkopolski NP, whereas the declines in 2020, in relation to 2019, exceed 10% (3-5 umol/m\({}^{2}\)) for Magurski, Ojcowski, Wielkopolski, and Gory Stolowe national parks. The mean annual NO\({}_{2}\) concentration for all landscape parks ranged from 34 umol/m\({}^{2}\) (2020) to 36 umol/m\({}^{2}\) (2020). It exceeded 40 umol/m\({}^{2}\) in the case of 40 parks. In 2021, it ranged from 20 to 60 umol/m\({}^{2}\). The mean annual NO\({}_{2}\) content for all tourist regions changed from 28.6 umol/m\({}^{2}\) (2020) to 31.5 umol/m\({}^{2}\) (2021). It exceeded 40 umol/m\({}^{2}\) in only two regions. The highest NO\({}_{2}\) concentrations occurred in the following tourist regions: Krakow-Czestochowa (55 umol/m\({}^{2}\)), Swietokrzyski (42 umol/m\({}^{2}\)), Walbrzych (38 umol/m\({}^{2}\)), Kazimierz Dolny-Naleczow (37 umol/m\({}^{2}\)), and Lagow (37 umol/m\({}^{2}\)). The lowest concentrations were found in the following regions: Rymanow-Zdroj (22 umol/m\({}^{2}\)), Tatra-Podhale (24 umol/m\({}^{2}\)), Gorice (24 umol/m\({}^{2}\)), Gorice-Luban, and Suwakli-Augustow (25 umol/m\({}^{2}\)). The highest increase (in 2021 compared to 2020) was found in the following regions: Koscierzyna-Kartuzy and Iawa-Ostroda (17%), Krakow-Czestochowa, Brodnica, and Walbrzych (15%). A 1% to 4% increase occurred in the Zywiec, Rymanow-Zdroj, Lagow, and Gorce-Luban regions. In 2021, mean NO\({}_{2}\) content in these regions fell by 4% to 8% in relation to 2019.