environmental exposure measurement time spent outdoors measurement true https://doi.org/10.1101/2021.09.02.21262942 0000-0001-8222-008X https://biobank.ndph.ox.ac.uk/crystal/field.cgi?id=1050 https://biobank.ndph.ox.ac.uk/crystal/field.cgi?id=1060 Quantification of time an individual spends outside.