Fig. 7b shows a weak correlation between PM2.5 and coarse PM for the light-rail stations and train (R2 = 0.21), suggesting that they do not share a common source. However, given the temporal variation of ambient air and its strong influence on the personal PM exposure levels of the light-rail line (Fig. 5c and d), the data points presented in the figure, which represent the average of the 7 days of sampling, do not account for this significant factor. To account for the day-to-day variation of light-rail line PM concentrations, a linear regression of the daily fine and coarse PM levels was conducted for each station and the train (N = 7).