Abstract:In public places many countries banned smoking as the most important indoor source of fine airborne particulate matter. In Austria partial bans have been in force since 2009, with exemptions for the hospitality industry. From February to October 2010 we investigated PM 2.5 concentrations in the breathing area of guests in well frequented Viennese establishments of all sizes, and compared these chance indoor samples with PM 2.5 concentrations measured during the same half hour at the next outdoor monitoring station. The laser particle counter (OPC1.108, Grimm ® ) used for indoor measurements had been calibrated by ß-attenuation (FH 62 I-R, Eberline ® ), which was used outdoors. 48% of 112 venues visited did not fully comply with the law, notwithstanding its weakness. Highest median concentrations (in µg/m³ ) were found in bars (443.7), followed by nightclubs/discotheques (421.1), pubs (147.7), cafes (106.1) and restaurants (23.4). Concentrations increased with number of smokers present (p < 0.01), with medians of 282.4/241,3/67.6/6.9 µg/m³ in smoking venues/smoking rooms/adjacent non-smoking rooms/exclusive non-smoking venues. Only for the latter, a significant correlation was found with outdoor concentrations (r = 0.48, p < 0.01), while concentrations in non-smoking rooms were higher (p < 0.01) and unrelated to outdoor concentrations, but significantly dependent on concentrations in the adjacent smoking room (r = 0.64, p < 0.01). In conclusion, the partial smoking ban failed and guests of Viennese hospitality venues continue to risk disease from passive smoking, even in so-called "non-smoking rooms", which are second-hand smoke rooms. OPEN ACCESSAtmosphere 2011, 2 172