# Appendix M

. 4

Procedures for Developing and Displaying AoI

Back-trajectory Residence Time GIS Data

Tennessee Department of Environment and Conservation

Division of Air Pollution Control

9 th Floor L&C Annex

401 Church Street Nashville, TN 37243Procedures for Developing and Displaying Ao I Back-trajectory Residence Time GIS Data 29 August 2007

The development of the GIS databases for the VI STAS Area of Influence (AoI) analyses were accomplished through the application of a set of Linux Perl scripts and Arc Macro Language (AML) scripts executed within ESRI ’s Arc/INFO GIS. Specific steps in the development of the

GIS data and the associated di splays are provided below:

Back-trajectory Residence Time GIS Coverages

1) Back-trajectory Residence time data were received from ARS as ASCII GRID formatted

data files. Included were the raw counts in each grid cell as well as extinction weighted

residence time counts. Residence time data weighted by total extinction, as well as constituent species extinction, were provi ded on a uniform 1 degree by 1 degree unprojected (i.e. geodetic) coordinate system.

2) Linux Perl scripts are used to re-format th e ARS back-trajectory residence time datasets for import to Arc/INFO

3) A polygon coverage was define d in Arc/INFO to represen t the geodetic 1 degree by 1 degree gridded domain for the residence time da ta. The reformatted datasets are then joined to this polygon coverage using the I and J cell indices as the join item.

4) The residence time polygon coverage is then re-projected to the RPO Unified Grid Lambert Conformal Projection c oordinate system. The RPO LCP coordinate system is

defined as follows:

Projection LAMBERT

Datum NONE Units METERS Spheroid SPHERE

Parameters: 1st standard parallel 33 0 0.000
2nd standard parallel 45 0 0.000

central meridian -97 0 0.000 latitude of projection's origin 40 0 0.000 false easting (meters) 0.00000 false northing (meters) 0.00000

Figure 1 displays the result of re-proj ecting the raw back-trajectory residence time data. Displayed are the raw counts (bcnt) in each 1 degree by 1 degree grid cell.

5) The resulting polygon coverage is then aggregated to 36-km grid cells on the RPO LCP coordinate system using an area-weighting interpolation scheme using the Arc/INFO STATISTICS command. Figure 2 displays the associated result of st ep 4 overlayed with the 36-km modeling grid cells. The area fr actions for each polygon are also displayed, and in Figure 3, the raw trajectory counts ar e also displayed for each re-projected 1 degree by 1 degree grid cell. Area fractions ar e defined as the ratio of the area of eachpolygon resulting from the intersection of th e two grids to the area of the 36-km modeling grid cells. Note that for modeling grid cells that lie entirely within the 1-degree by 1-degree cell, the area fr action is equal to 1.0. The re sult of the area-weighted interpolation is displayed in Figure 4. For the grid cell in the center of the display, the

calculation is as follows:

761*0.5208 + 1798*0.4792 = 1257.95

Other back-trajectory data (total extinction-weighted residence time, sulfate extinction- weighted residence time, etc.) are treated si milarly to obtain a 36-km gridded data set in the RPO LCP coordinate system.

6) Residence time back traject ory data (raw counts and extinc tion-weighted data) are further weighted by inverse distance (1/r) from each gr id cell to the location of the corresponding

IMPROVE monitor site. The distances are cal culated as the linear distance from each grid cell center to the IMPR OVE monitor. The grid ce ll corresponding to the IMPROVE monitor location is given a weight of 1/9. The value of 1/9 was chosen, somewhat arbitrarily, to represent the nominal distan ce a trajectory travels across the grid cell containing the monitor. Although the exact lo cation of the monitor is known, because the gridded datasets are representative of grid cell averages across the 36-km by 36-km cells,

the decision to use a value of 9 (i.e., 1⁄4 of the distance acro ss a grid cell) was made in order to be fairly consistent with the distan ces to the center of all other grid cells. The distance weighting factors are displayed in Figur e 5. Note that the distance factor for grid

cell with the monitor is set to 9 internally in the processi ng script, over-riding the distance as displayed in Figure 5. Note also that the distance weighted back-trajectory residence time are not displayed; these data are calculated at this processing step in order to export the data as text files for further proce ssing and analysis outside of the GIS.

7) The resulting coverage is then over-laye d with county boundaries and the following data fields are exported to an ASCII comma-delim ited text files for further processing and analyses: I, J, County FIPS, raw count, total ex tinction-weighted RT, sulfate extinction- weighted RT, total extinction-weight ed, distance-weighted RT, and sulfate extinction-weighted, distance-weighted RT.

Displaying Back-Trajector y Residence Time Data

Displays of back-trajectory residence times ar e generated from the GIS coverage described above using Arc/INFO as follows:

1) In the current analysis, only sulfate extin ction-weighted back-tra jectory residence times are considered. For each grid cell, the sulf ate extinction-weighted back trajectory is scaled by the maximum value of total exti nction-weighted residence time across the entire domain. The result is re-cast as a percentage by multiplying by 100. Note that these data, as displayed, are not weighted by distance. In the example shown, thedomain-wide maximum total extinction-weight ed back-trajectory residence time has a

value of 176620. This value is used as a sca ling factor for the data displayed. Figure 6 displays the sulfate extinction-weighted, back-t rajectory residence times, re-projected and allocated to the 36-km modeling grid cells, and scaled by the maxi mum value of total extinction-weighted residence time. Therefor e the plots display the sulfate extinctionweighted back-trajectory residence times as a percentage of the domain-wide maximum total extinction-weighted back -trajectory residence times.

2) The boundaries of the extent of the sulfate extinction-weighted back -trajectory residence time, scaled by the maximum total extincti on-weighted residence times (as computed above), for values greater then 2%, 5% and 10% are generated using the RESELECT command in Arc/INFO by extracting all grid ce lls meeting the specified criteria (i.e., > 2%; > 5%; and > 10% of the maximum total extinction-weighted residence time across the domain)

3) Graphical displays are generated of the su lfate extinction-weighted residence times based on the coverages described above. The boundari es of the 2%; 5% and 10% contours in these data are drawn on the displays in re d (>10%), orange (5%) and blue (>2%) and shaded with varying degrees of grey. Thes e data are plotted using intervals of 2, 5, 10, 20, 30, 40 and 60%.

4) The location of the IMPROVE monitor fo r each Class I Area is noted by drawing

concentric circles centered on the monitor with radii of 100 and 200 kilometers. A separate point coverage defining the locati on of the IMPROVE monitors is used to facilitate this step.

5) Finally, county boundaries are over-layed and various labels are added to the displays. The final sulfate extinction-weighted back-t rajectory residence times are displayed in Figure 7 for Everglades Nati onal Park. Note the maximum total extinction-weighted back-trajectory residence time value (176620) and the maximum values of the data displayed (43%) shown in the legend.

Gridded Emissions x Back-Trajector y Residence Time GIS Coverages

1) The VISTAS 36-km gridded point source emi ssions data are imported into Arc/INFO as a polygon coverage at 36-km resolution in th e RPO LCP coordinate projection system. Figure 8 displays the gridded SO2 point source emissions on the 36-km modeling

domain.

2) For each species in the emission data file , and for each extinction-weighted residence time value, new items are added to the cove rage and the product of emissions times extinction weighted back-traje ctory residence times is computed on a grid-cell by gridcell basis. Both distance-weighted and non- distance-weighted data are calculated and added to the polygon coverages. Figure 9 di splays the total extin ction-weighted backtrajectory residence time data, re-projected and interpolated to the 36-km grid cells. Also displayed in Figure 9 are the values from the 1-degree by 1-de gree raw data (labeled in blue). Figure 10 displays these data wei ghted by distance. The cell-by-cell product of SO2 emissions and total extinction-weighted residence times are displayed in Figure 11, while Figure 12 displays these data weight ed by inverse distance from the monitor.

3) The sum of each of these items across the entire modeling domain is computed (using STATISTICS) and used to normalize each grid-c ell value and re-cast as a percentage by multiplying by 100. In the example, this sum is computed as 53512390. The final result of this normalization step is displayed in Figure 13. The calcu lation is as follows, for the sample grid cell displayed in the center of Figure 13:

100 * [BEXT_RT *(1/R)*SO2] / Sum(BEXT_RT*(1/R)*SO2)

100 * [113191.56 * (1/50.91) * 8989.56] / 53512390 = 37.34

Displaying Normalized Emissions x Distance-W eighted Back-Trajectory Residence Time Data

Displays of emissions x back-trajectory residence times are generated from the GIS coverage described above using Arc/INFO as follows:

1) In the current analysis, only total extinction-weighted back-trajectory residence times are considered. For each grid cell, the total extinction-weighted, distance-weighted back trajectory data is multiplied by the VISTAS point source SO2 emissions on a grid-cell by grid-cell basis.

2) The result of the previous step (SO2 * to tal extinction-weighted, distance-weighted backtrajectory residence times) is normalized by the sum across the entire domain. The result is re-cast as a percentage by multiplying by 100.

3) The maximum value of the resulting data of 2) above is computed using the

STATISTICS command in Arc/INFO. This value is displayed in the legends of the plots.

4) Graphical displays are generated of th e normalized SO2 emissions * total extinctionweighted, distance-weighted back-trajector y residence times based on the coverages described above. The boundaries of the 2%; 5% and 10% contours from the residence times data, as described above, are drawn on th e displays in red (>10% ), orange (5%) and blue (>2%) and shaded with varying degrees of grey. The emissions * residence times data are plotted using intervals of 0.2, 0.3, 0.4, 0.6, 0.8, 2.0 and 10.

5) The location of the IMPROVE monitor fo r each Class I Area is noted by drawing

concentric circles centered on the monitor with radii of 100 and 200 kilometers. A separate point coverage defining the locati on of the IMPROVE monitors is used to facilitate this step.6) Finally, county boundaries are over-layed a nd various labels are added to the displays. The final distance-weighted, normalized point source SO2 emissions * total extinctionweighted back-trajectory residence times are displayed in Figure 14 for Everglades

National Park. Note the maximum value of th e data displayed, from Step 3 above, (37%) shown in the legend.

Figure 1 . Raw back-trajectory residence time counts – re-projected to RPO LCPFigure 2 . Area fractions used in interpolation scheme.Figure 3 . Area fractions used in inte rpolation scheme with raw c ounts displayed in blue text.Figure 4 . Result of area-weight ed interpolation of raw counts to the 36-km modeling grid cells.Figure 5 . Distance weighting factors.Figure 6. Result of area-weighted in terpolation of sulfate extinction-weighted back-trajectory residence times to the 36-km modeling grid cells, scaled by the maximum total extinctionweighted back-trajectory residence time.Figure 7. Final display of sulfat e extinction-weighted back-t rajectory residence time for Everglades National Park.Figure 8 . Gridded point source SO2 emissions.Figure 9. Interpolated total extinction-weighted residence times.Figure 10 . Distance-weighted, total extinc tion-weighted residence times.Figure 11 . SO2 emissions times total extinc tion-weighted residence times.Figure 12 . Distance-weighted, SO2 emissions times to tal extinction-weighted residence times.Figure 13 . 100 * Distance weighted, nor malized, SO2 emissions times total extinction-weighted

residence times.Figure 14 . Final display of normalized distance-weighted, SO2 point source emissions * total extinction-weighted back-tra jectory residence time for Everglades National Park.