The grass pollen season 2015: a proof of concept multi-approach study in three different European cities - Kmenta Maximilian; Bastl Katharina; Berger Uwe; Kramer Matthias F; . Heath Matthew D; Pätsi Sanna; Pessi Anna-Mari; Saarto Annika; Werchan Barbora; Werchan Matthias; Zetter Reinhard; Bergmann Karl-Christian (BIOMED CENTRAL LTD, 2022)