Implementing EKMA: Step 3

Several documents are available for your perusal prior to running the OZIP model. This document attempts to provide a "quick start" to use of the modeling tool. The documents below are intended as a reference resource and/or for those who wish to download, compile, and run the OZIP code on your own machine:

OZIP is a modeling tool that is used to prepare isopleths (lines of equal concentrations) as a function of the concentrations of the precursors NOx and VOCs. In general, the following input variables are required:

  1. Light intensity
  2. Dilution
  3. O3 transport
  4. Precursor transport
  5. Emissions
  6. Reactivity

Light intensity

Light intensities are calculated within the OZIP program as a function of the inputted variables of latitude, longitude, day of the year, and time zone. The program uses a concept of local civil time, or LCT. LCT is the same as local standard time for areas that do not switch to Daylight Savings Time.

In addition to the values provided by the user, the modeler also has the option of two zenith sets, one generated by a program called JSpec640 by Harvey Jefferies at UNC-Chapel Hill, and the other used by the Regional Acid Deposition Model (RADM). This scenario has been developed using the JSpec640 values, but the RADM zenith set is included for other studies not addressed in this scenario.

Both zenith set options generate best-fit values of the photolytic rate constants. The first reaction in ozone formation is:

NO2 + hv -----> NO + O

which proceeds at a rate determined by the light intensity. Light intensity is, as described briefly above, dependent on location and time of year. These values are provided under Title and Initial Settings in the OZIP Web interface form

Dilution

Dilution depends on the rise of the mixing height, defined as the top of the column of air which originates at the surface. The air within this column is assumed to be well-mixed from mechanical and thermal turbulence. Mixing height is determed by four variables in OZIP:

  1. the 0800 LCT mixing height
  2. the maximum mixing height (either given or calculated)
  3. the time at which the mixing height begins to rise
  4. the time at which the mixing height reaches its maximum

The OZIP Web Interface provides the modeler with the opportunity to supply these values under the Meteorological Conditions section.

O3 transport

Ozone can be transported into the study area by two mechanisms:

  1. advection of ozone along the earth's surface
  2. advection of ozone aloft, typically at night and during the early morning hours

Of the two, overnight transport of ozone aloft is the most significant. The recommended procedure for EKMA/OZIP is to set the O3 transport value at the surface for 0.00 ppm. O3 transport aloft is set at the height at which the ozone enters the column and the concentration in ppm.

Precursor transport

Typically, transport of precursor pollutants into the column are not considered important, but can occur at the surface and aloft, in a manner similar to ozone. NOx, VOCs, and CO are the common precursor pollutants described under the Transport section of OZIP.

Emissions

In OZIP, we need to describe the emissions coming into the column once the column begins moving, typically after 0800 (8 am). There are a number of recommended procedures for generating this "emissions inventory" for inclusion into OZIP and other photochemical models. In OZIP, an emission is provided for each emitted species at the beginning of each hour of the simulation. The bad news is that this emissions inventory must be converted into an emissions fraction inventory. The good news is that this conversion feature is built into OZIP. The user must provide:

The OZIP form provided for this scenario gives the modeler a choice of a default mass emissions profile, or a customizable profile. In both choices, the species to be profiled include:

In the OZIP interface, the modeler has the option of including one, several, or all of these species for inclusion in the model run.

Reactivity

Reactivity refers to the choice of a chemical reaction series, or mechanism. Typically the EKMA procedure uses the Carbon-Bond IV (CB4). The Web form provides the user with the additional choice of a RADM mechanism for further study as desired. The choice of a reactivity mechanism is provided in the Required Data Sets part of the form. A more complete description of these mechanisms is provided elsewhere

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