## Concentration / Display / Time-of-Arrival

Time of arrival graphic (isochron) shows the time after the start of the simulation that the concentration exceeds the given threshold concentration at each concentration grid cell. The default contour interval (-1) uses the concentration averaging period. Otherwise, the time difference field should be set to hours.

The GUI and the command line options are similar with the command line syntax as follows: USAGE: isochron -[options(default)]

-i[input file name (cdump)] : the input file needs to contain multiple time period
-o[output name (chron)] : the output file represents all time periods
-t[threshold value (1.0E-36)]
-c[color fill no:0 yes:(1)] : the =0 option results in contours
-f[frames: (0)-all frames one file, 1-one frame per file] : multiple frames can only be due to multiple levels or species in the input file
-n[number of contours (10)] : only 12 contours fit across the display
-d[difference in hours between contours (-1)]
-j[graphics map background file (arlmap)] : the shape file option is not available

In the 240 hour duration example simulation shown below, the concentration field was output every six hours, the contour interval was set to 24 hours and the number of contours was increased from 10 to 12. The one hour duration release took 120 h to reach the east coast of the US and 240 hour to reach northern Europe.