“…Additional published data from 18 countries were included from a European-wide trend study concerning Ambrosia pollen (Sikoparija et al, 2017). Further data were included from studies conducted in Germany (Buters et al, 2015;Höflich et al, 2016;Melgar et al, 2012), Croatia (Bokan et al, 2007;Liu et al, 2016;Menut et al, 2014;Peternel et al, 2006;Puljak et al, 2016), Turkey (Acar et al, 2017;Altintaş et al, 2004;Bicakci and Tosunoglu, 2015;Tosunoglu and Bicakci, 2015), Romania (Leru et al, 2018), Russia (Severova et al, 2015;Shamgunova and Zaklyakova, 2011), Serbia (Josipović and Ljubičić, 2012), Ukraine (Maleeva and Prikhodko, 2017;Rodinkova, 2013;Turos et al, 2009), Bosnia (Turos et al, 2009) and Slovakia (Hrabovský et al, 2016). All these sites are located within urban zones and data are collected from the top of a building, typically 10 m-20 m above ground level.…”