Source of Variation d.f. Pr > F F value Site 6 0.0001*z 21.57 Speed (Site) 7 0.0001** 5.22 Height (Site) 7 0.0001** 16.58 Speed*Height (Site) 7 0.0168* 2.51 C.V. (%)   80.89   Mean (mg/m3)   1.035   zObserved level of significance (Pr > F: *, **) at 0.05, and 0.01 significant effect, C.V.=coefficient of variation, d.f.=degree of freedom

Table 9: Analysis of variance for the PM measured with sticky tape technique at different time intervals when a vehicle was running at three speeds at sites in Mexico and the US.