... In- vehicle Bus Indoor 25 (7) 25 (7) 26 (7) 27 775 (14079) Mall 28 (9) 28 (9) 33 ( 12) 24 2 72 (1 022 7) 40 ( 12) 40 ( 12) 50 (14) 21 4 62 (65 92) Bus-stop 35 (7) 35 (7) 43 ( 12) 51436 (13639) Sidewalk 32 ... In- vehicle Train Indoor 34 (3) 34 (3) 37 (4) 12, 789 (2, 577) Mall 27 (5) 27 (5) 32 (6) 20 ,835 (5 ,22 2) Platform 26 (4) 27 (4) 31 (5) 9,570 (1,930) 21 (4) 22 (4) 24 (4) 13,833 (2, 6 72) 28 (7) 28 (7) 30 ... PM2.5 (top) and PN (middle) concentrations, and PM2.5/PM10 ratio (bottom) during the Walk mode trip on 20 May 20 13 1 02 Figure 4 -24 : Spatial variation in PM2.5 (top) and PN (bottom) concentrations...