## 2 Materials and Methods
The one from 2020 was chosen because of its higher R\({}^{2}\) value: y = 1.689x + 22,932 (R\({}^{2}\) = 0.71). A similar level of agreement between the ground and satellite station data was obtained by [PERSON] et al. (2013), [PERSON] et al. (2010), and [PERSON] et al. (2013). Figure 1: Location of tourist reception areas. (a) National parks: A—Babiogóski, B—Bialowieski, C—Biebrzanski, D—Bieszczadzki, E—Drawierski, F—Gorczanski, G—Kampinoski, H—Karkonoski, I—Magurski, P, [PERSON]—[PERSON], [PERSON]—[PERSON], [PERSON]—[PERSON], [PERSON]—[PERSON], N—[PERSON], O—[PERSON], P—Poleski, Q—Roztoczanski, R—Slowinski, S—Swietokrzyski, T—Tatrzanski, U—Wielkopolski, V—Wigierski, and W—Wolinski. (b) Tourist regions: I—Brodnica, II—Gdarsk, III—Gorce–Lubar, IV—Gorice, V—Iwas-Ostroda, VI—Jelenia Gora, VII—Kazimierz Dolny-Nalcezow, VIII—Klodzko, IX—Kolobrzeg, X—Koscierzyna-Kartuzy, XI—Krakow-Czestochowa, XII—Lagow, XIII—Rymanow-Zdroj, XIV—Novy Sacz, XV—Suwäski-Augustow, XVI—Szczecin, XVII—Swietokrzyskie, XVIII—Tatra-Podhale, XIX—Wabrzych, XX—Great Mazurian Lakes, and XXI—Zywiec. (c) Provincial capitals. (d) Health resorts: 1—Augustow, 2—Busko-Zdroj, 3—Ciechocinek, 4—Cieplice, 5—Czerniawa-Zdroj, 6—Dabki, 7—Dhugopole-Zdroj, 8—Dusznik-Zdroj, 9—Goczalkowice-Zdroj, 10—Goldap, 11—Horyniec-Zdroj, 12—Innowroclaw, 13—Iwonicz-Zdroj, 14—Jedlina-Zdroj, 15—Kamien Pomorski, 16—Kolobrzeg, 17—Konstancin-Jeziorna, 18—Krasnobrod, 19—Krynica-Zdroj, 20—Kudowa-Zdroj, 21—Ladek-Zdroj, 22—Muszyna, 23—Nalcezow, 24--Piwniczna-Zdroj, 25—Polancz-Zdroj, 26—Polanczyk, 27—Polczyn-Zdroj, 28—Przzerzczyn-Zdroj, 29—Rabka-Zdroj, 30—Rymanow-Zdroj, 31—Solec-Zdroj, 32—Sopot, 33—Suprash, 34—Swoszowice, 35—Szczawnica, 36—Szczawno-Zdroj, 37—Swieradow-Zdroj, 38—Swinoujš  
The annual mean NO\({}_{2}\) concentration limit, 40 \(\mathrm{\SIUnitSymbolMicro}\)g/m\({}^{3}\) (2008/EC/50), set by the EU and GIOS [35], corresponds to 91 \(\mathrm{\SIUnitSymbolMicro}\)mol/m\({}^{2}\) (satellite data). In turn, research by [PERSON] et al. [36] suggests that the effect of NO\({}_{2}\) on COVID-19 mortality was already evident at the level of about 20 \(\mathrm{\SIUnitSymbolMicro}\)g/m\({}^{3}\), which corresponds to about 57 \(\mathrm{\SIUnitSymbolMicro}\)mol/m\({}^{2}\) for the satellite data. Even lower values were indicated in September 2021 by the World Health Organization, according to which the mean NO\({}_{2}\) concentration should not exceed 10 \(\mathrm{\SIUnitSymbolMicro}\)g/m\({}^{3}\)[37]. This corresponds to 40 \(\mathrm{\SIUnitSymbolMicro}\)mol/m\({}^{2}\) in the case of satellite data. In the analyses carried out in the present study, we referred to this concentration as a limit. At this point, it should be noted that, according to a study by [PERSON] et al. [33], TROPOMI sensor data are slightly underestimated compared to ground-based measurements in the case of high pollution. The adoption of lower concentrations as a limit is justified from this point of view. In addition to assessing the spatial and temporal variation in NO\({}_{2}\) content in tourist reception areas, an attempt was also made to evaluate the impact of the amount of nitrogen dioxide air pollution on the number of deaths.