Averaged upwind residence time distributions over different geographical regions (a)and vertical levels (%) (b) for 3 hourly retroplumes in 2010 simulated by FLEXPART. Note that not all transport sources and heights are included in the legends, and therefore total percentages are less than 100% in the upwind days. NA: North America; NATL: North Atlantic; AF:Africa; EU: Europe. DOI: https://doi.org/10.1525/elementa.194.f2