Info

" See Title 13, California Code of Regulations, Section 1960.1(g)(1).

h RF-A is industry-average gasoline; RFG is California reformulated gasoline; M85 is a mixture of 85% methanol, 15% gasoline, CNG = compressed natural gas; LPG = liquefied petroleum gas.

supra), it is important to establish whether the same values for the various reactivity measures would be obtained using an airshed model. Russell and coworkers have applied the C1T airshed model to this problem and concluded that there is some difference, but it is small, < ± 15%, and is primarily due to temporal and spatial differences in the emission patterns (McNair et al., 1994; Russell et al., 1995). Chang and Rudy (1990a) have also shown that this approach should be valid even if the total VOC emissions are substantially altered. Other uncertainties in the reactivities due to uncertainties in the kinetics and mechanisms are discussed by Yang et al. (1995, 1996).

This approach has also been applied to sources other than automobiles to assess the relative importance of various organics and sources. For example, Blake and Rowland (1995) used the concept of maximum incremental reactivity to assess the relative importance of various organics in Mexico City. They concluded that liquefied petroleum gas was a major contributor to ozone formation and that relatively small fractions of highly reactive alkenes in the gas contributed disproportionately to ozone formation.

The application of reactivity approaches to consumer products is discussed in detail by Dimitriades (1996).

Analogous approaches to assessing VOC reactivities have been developed by Derwent and co-workers (e.g., see Hough and Derwent, 1987; Derwent and Jenkin, 1991; and Derwent et al., 1996) where a trajectory model is used to calculate the additional ozone production due to the addition of a particular VOC under conditions typical of air masses advected across northwest Europe toward the British Isles. The photochemical ozone creation potential (POCP) index thus calculated is a measure of the reactivity of the particular VOC in terms of 03 formation. Andersson-Skold and co-workers (1992) followed a similar approach for the summer conditions in southern Sweden.

Table 16.12 compares the POCP values derived by Derwent et al. (1996, 1998) and Andersson-Skold et al. (1992) to the MIR approach of Carter (1994). While the general trends in reactivities predicted by each approach are qualitatively similar, there are quantitative differences. For example, the POPC values for the simple alkanes relative to ethene are larger than the MIR values. This reflects in part the details of the mechanisms used in the calculations and the time scale over which the reactions are followed as well as differences in the assumed pollutant mix into which the VOC is injected, such as the VOC/NO, ratio.

In short, the application of the principles of varying reactivities of organics as one component of the development of cost-effective control strategies is increas-

TABLE 16.12 Some Measures of Reactivity for Various Organics"

HC or VOC

MIR11

POCP'

POCPrf

Methane

0 0

Post a comment