Source of Variation d.f. T1 T5 T10 T15 T20 T25 T30 Sum Site 6 0.0001**z 0.0001** 0.0001** 0.0001** 0.0001** 0.0001** 0.5349 0.0001** Speed 2 0.0001** 0.0010** 0.1301 0.4990 0.5505 0.3388 0.3006 0.0001** Speed (site) 12 0.0040** 0.1562 0.2658 0.5586 0.6980 0.3507 0.3678 0.1486 C.V. (%)   56.4 113.8 198.4 266.1 354.32 410.8 678.1 84.8 Mean (mg/m3)   5.864 3.417 1.294 0.643 0.433 0.271 0.08 11.96 zObserved level of significance (Pr > F: **) at 0.01 is considered highly significant effect, C.V.=coefficient of variation. d.f.=degree of freedom, T1 to T30 are times readings at 1 to 30 sec

Table 6: Analysis of variance for the PM2.5 detected by the DustTrak instrument at different time intervals when a vehicle was running at three speeds at several sites in Mexico and US.