As to collect samples of fine and ultrafine particle concentration before introducing the smoking-ban, first study measurements were performed from April to October 2019 in 40 randomly chosen, well frequented catering facilities of different types, such as pubs, restaurants, bars, discotheques and cafeterias in Vienna. 11 From November 2019 to March 2020, the measurements were repeated, visiting the same venues considering approximately similar settings, including the same rooms, related time of the recordings and similar weekdays (differencing between days during a week and the weekend), however, to well frequented times (cafes in the afternoon, discotheques at night). One venue of the first study had to be excluded in the second study, because it was closed, whereas recordings were taken in 39 gastronomy facilities before COVID-19 shutdown started. Each facility had separate smoking and non-smoking areas before November 2019, hence in each area a measurement was undertaken. Each recording lasted 20-30 minutes and, such as to avoid selection bias from permission, was unannounced and hidden while consuming. As devices, GRIMM® Aerosol Spectrometer 1.108 for fine particulate matter, detecting particles bigger than 300 nanometres, and MiniDiSC®, detecting particles of 10-300 nanometres in diameter, for ultrafine particulate concentration were chosen. Measurement methods were described earlier. 16171819

After collecting the data, the differences of concentrations between these two (formerly) areas were analysed and the differences of concentrations before to after introducing the smoking ban. The various mean concentrations of both studies were compared using statistics, including primarily paired t-testing as well as visual descriptions like boxplots via IBM SPSS Statistics Subscription®. The results were assessed to a confidence interval of 95%, therefore, contrasted against the significance level of p=0.05.

Contrasted against p=0.05, statistics show statistically significant declines of fine particle concentrations of PM10, PM2.5 and PM1 in former smoking areas as well as of PM2.5 and PM1 in former non-smoking areas, as shown in Table 1 and Figure 1. As for ultrafine particle concentration, statistically significant declines of PNC were registered in former smoking areas. In former non-smoking areas, the PNC decline was not significant. Considering LDSA, in both areas statistically significant declines were shown (Table 2, Figure 2, Figure 3).

Fine and ultrafine particle concentrations after introducing the smoking ban were not significantly different between the former smoking and former non-smoking areas. (Table 3 and Table 4, Figure 4, Figure 5, Figure 6)

Overall, concerning the comparison before to after the introduction of the smoking-ban, in each area were found remarkable declines of fine as well as ultrafine particle concentrations, statistically significant in smoking areas for PM10, PM2.5, PM1, PNC and LDSA and in non-smoking areas for PM2.5, PM1 and LDSA. No statistically significant declines were registered in non-smoking areas for PM10 and PNC. After the ban, there were no significant differences of concentrations found anymore between former smoking and non-smoking areas.

In comparison to the smoking areas before the ban statistically significant declines of fine and ultrafine particle concentrations indicate reduced passive smoking in the Viennese hospitality industry, which is a successful development. Also, these results underline the effectiveness of the new legislation to protect the population against the harmful effects of fine and ultrafine particles from second-hand smoke. The decline of PM10 in former non-smoking areas was not significant, which might be due to renovation and other sources of PM10, stirred up and resuspended by walking of guests and waiters. The high variance of PNC in the non-smoking area might have been due to illegal smoking shortly before the air sample was taken, which could explain some very high concentrations at single venues, especially if concomitant with high LDSA and PM1 in the room. But the big variance of PNC in the non-smoking area could partly be explained also by other possible combustion (e.g. candles which have been excluded at the table of the researcher only) and condensation products, highly variable in time and space.

Prior to the smoking ban indoor smoke exposures were highest in the smoking rooms, followed by adjacent rooms and lowest outdoors. There were no significant differences in concentrations between the smoking and non-smoking areas after the smoking ban entered into force. Therefore, one could diagnose that the indoor air quality was considerably improved. 1112 However, some outliers in this study after the ban show the necessity of repeated controls in Vienna. Also, outside Vienna the compliance with the law should be controlled in the Austrian hospitality industry. The goal should be the enforcement of the law in all hospitality venues, complete disappearance of ash trays indoors and at the entrance, indoor air concentrations of PM2.5 below 25 µg/m^³3 and PNC below 10,000 pt/cm^³18.