Figure S1. Histagram showing the fequency of the percentage of 500 HYSPLIT particles released for each flask receptor that remain inside the HYSPLIT domain over 10 day back trajectories, separated by season (subpanels) and region (colors correspond to Figure 1 ). The mean percentage across flask receptors is shown within each panel, along with the mean elapsed time (in days) of particles that either reach the boundary (< 10 days) or stay within domain (10 days). This shows that a very small percentage of particles (< 10%) stay within the domain in winter, independent of region, with most particles exiting the domain in ~5 days. More particles stay within the domain in summer, but the percentage is more variable across regions than in winter.