EKMA model

FIGURE 16.14 Typical peak ozone isopleths generated front initial mixtures of VOC and NO, in air. (a) Two-dimensional depiction generated from the EKMA model (Dodge, 1977a) (b) three-dimensional depiction prepared by B. Dickerson. The VOC-liniited region (e.g., at point D) is found in some highly polluted urban centers while the NOA (e.g., at point A) is typical of downwind suburban and rural areas (adapted from Finlayson-Pitts and Pitts, 1993). 

From Carter and Atkinson (1989) calculated using the EKMA model with low dilution and an eight-component surrogate mixture of organics chosen to be representative of emissions into California s South Coast air basin. Note that the absolute values used may have changed for some components since the original publication due to further refinement of the model. 

Fig. 7.11 Ozone isopleths for the maximum concentration of O3 obtained by (a) a smog chambtr experiment after long-time irradiation to reach ultimate maximum (Sakamaki et al. 1982), and (b) EKMA model with limited-time irradiation to simulate daily ozone (Dodge 1977)...

For the purpose of EKMA modeling, hydrocarbons include only nonmethane hydrocarbons (NMHC), or nonmeihane organic carbon (NMOC) methane is excluded due to its comparatively low reactivity. The concentration of NMHC in an air sample is usually expressed in terms of the moles of carbon per mole of air, denoted ppmC or ppbC (parts per million carbon or parts per billion carbon). For any hydrocarbon, its air concentration in ppm(v) or ppb(v) can be converted to ppmC or ppbC by... 

Using Fig. 4.41 and the above concentrations of NO and NMHC, the corresponding ozone concentration is 0.16 ppm. Actual values in this open rural area would probably be lower, because the EKMA model is based on steady-state conditions, which may not be achieved during the relatively short travel time from the well to the point of measurement. Furthermore, chemical dilution due to plume dispersion is not accounted for in EKMA modeling. 

Box models (including EKMA) One type of simple model that has been applied to predict pollutant concentrations is known as the box model (Fig. 16.19) (e.g., Schere and Demerjian, 1978). The air mass over a region is treated as a box into which pollutants are emitted and undergo chemical reactions. Transport into and out of the box by meteorological processes and dilution is taken into account. 

The kinetic modeling nomenclature arises from the incorporation of chemical kinetic submodels in EKMA. The empirical term comes from the use of observed 03 peaks in combination with the model-predicted ozone isopleths to develop control strategy options. Thus, the approach historically was to use the model to develop a series of ozone isopleths using conditions specific for that area. The second highest hourly observed 03 concentration and the measured... 

Because the values of IR and MIR shown in Tables 16.8 and 16.9 were developed using the EKMA box model tested against environmental chamber data (vide... 

Dimitriades, B., and M. Dodge, Eds., Proceedings of the Empirical Kinetic Modeling Approach (EKMA) Validation Workshop, EPA Report No. EPA-600/9-83-014, August 1983. 

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