OZIP simulates complex chemical and physical processes of the lower atmosphere through use of a trajectory model. The physical representation is a well-mixed column of air extending from the ground to the top of the mixed layer. This idealized air column moves with the wind (along the wind trajectory), but cannot expand horizontally. Emissions from the surface are included as the air column passes over different emission sources, and air from above the column is mixed in as the inversion rises during the day. Very complex chemical mechanisms may be input into OZIP to describe the chemical processes that occur within the modeled air mass.
Besides individual trajectory simulations, the program can use the EKMA procedure to automatically estimate the amount and type of recursor emission reductions required to achieve a specified ozone level. The ozone level currently defaulted in EKMA is a one-hour average maximum concentration of 0.12 ppm, the national ambient air quality standard. In the EKMA procedure, OZIP performs multiple simulations with different levels of organic and NOx precursor emissions to estimate the effect of reduced emissions on maximum ozone concentrations.
OZIP can also perform a specified set of simulations to calculate ozone levels at fixed intervals. This allows for the plotting of fixed ozone concentration lines (isolines) as a function of initial precursors. A post-processor program using gnuplot as a visualizer is used to control isopleth diagrams, plot options, display results, and provide output to the Web interface.
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