It is evident that f0 is the value of function (3) for the instant t =0 [namely:f0=fcold (t =0)], but it would be very hard a matching with the measured cold emissions at initial time, because of an imprecise continuous sampling during the first instants of the cold transient. The usefulness of this value, instead, is derived from the remark that it can be intended constant with the variation in driving cycles, as it represents the emission level at the initial instant and then it’s function only of the particular vehicle, pollutant and ambient temperature. In effect, it is evident in Table3 that the values of f0
calculated with this method vary not meaningfully with the diverse driving cycles. In order to validate all these procedures, the cold-start extra emission was successively calculated by employing the cold cumulative emission Eq. (4) for t =Treg, so achieving EC * (5), and the cold emission factor, in terms of mass per time unit, was calculated asecold * =EC * /Treg (6).