Central Campus Air Quality Model (CCAQM) Instructions

·         Link Geometry

o      Link Name - Optional. The user may define a 12-character description for the link.

o      Link Type - The user must select one of the following 5 choices to define the type of roadway that each link represents. (Click a cell in this column to view a drop list and select from the following 5 options.)

§      At-Grade -  For at-grade sections, CALINE does not permit the plume to mix below ground level, which is assumed to be at a height of zero.  The height of the link above the ground is defined in the Link Height cell.

§      Fill - For fill sections, CALINE4 automatically resets the link height to zero, and assumes that air flow follows the surface terrain, undisturbed.  This choice is functionally no different than the At-Grade choice with a link height defined as zero.  If you wish to model a link that is slightly elevated above ground, the At-Grade choice is more appropriate.

§      Depressed - For depressed sections, CALINE4 increases the residence time of an air parcel in the mixing zone.  The residence time increases in relation to the depth of the roadway depression. (Mixing zone = width of traffic lane(s) plus 3 meters on each side.)  In such a case, CO concentrations adjacent to the mixing zone are higher than those for an equivalent at-grade or fill section.  CO concentration drops more rapidly downwind of a depressed link because vertical mixing increases with residence time.

§      Bridge - For bridge sections, CALINE4 allows air to flow above and below the link.  The plume is permitted to mix downward from the link, until it reaches the distance defined in the Link Height cell.

§      Parking Lot - Parking lot links should be defined to be coincident with the parking lot access ways.  The CALINE4 algorithms adjust to account for the reduced mechanical and thermal turbulence anticipated from slow-moving, cold-start vehicles.

o      Link Coordinates - Links are defined as straight-line segments.  The entire length of each link should deviate no further than 3 meters from the centerline of the actual roadway. The endpoint coordinates, (x1, y1) and (x2, y2), define the positions of link endpoints.  The user must define the link geometry and receptor positions with a consistent Cartesian coordinate system. The position of the coordinate system origin is arbitrary and at the user's discretion.  The y-axis should be oriented north-south, with values increasing in the northward direction.  The x-axis should be oriented east-west, with values increasing in the eastward direction.

o      Link Height - For all link types except bridges, Link Height represents the height of the link above the surrounding terrain. Ground level is defined at 0 meters or feet (z=0).  The units of measure (feet or meters) are user-specified on the Job Parameters Page.  For at-grade links, the link height may be defined as 0 or a positive value.  For fill links, CALINE4 always treats the link as though its height was zero.  For depressed links, the depth of the depression should be indicated as a negative value. For parking lots, the link height should be defined as zero.  For bridges, Link Height defines the height of the bridge above the surface beneath it (a positive value), while the link itself is considered to be at z=0.

o      Mixing Zone Width - Defined as the width of the roadway, plus 3 meters on either side.  The minimum allowable value is 10 meters.

o      Canyon/Bluff Mix - users should leave the Canyon/Bluff input values set to zero, which disables the feature, since it is not applicable.