Exposure to green space and pollen allergy symptom severity: A case-crossover study in Belgium, Stas, Michiel, Aerts Raf, Hendrickx Marijke, Delcloo Andy, Dendoncker Nicolas, Dujardin Sébastien, Linard Catherine, Nawrot Tim, Van Nieuwenhuyse An, Aerts Jean-Marie, et al. , Science of The Total Environment, Jan-08-2021, Volume 781, (2021)