Hysplit: To test Dry Deposition of Gases in HYSPLIT using a built-in example

1. Prepare the Basic Run Setup (if not already done)
• Open the main Setup Run window.
• Set Total run time (hrs): e.g., 12 or 25 (tutorial uses 25 h for noticeable deposition).
• Set Direction: Fwd (forward).
• Add meteorology: Click Add Meteorology Files and select your file (e.g., oct1618.BIN).
• Click Setup starting locations → define 1 source (e.g., lat 40.0, lon -90.0, height 50 m, emission rate suitable for test).

2. Set Pollutant & Deposition (Gas Dry Deposition)
• In main setup → click Pollutant, Concentration Grid, and Deposition setup.
• Under Pollutant: Num=1, select Specie 1.
• Under Deposition: Num=1, select Specie 1 → this opens the Deposition Definition window.
• In Deposition window:
• Particle or Gas: Gas.
• Dry Deposition: Yes.
• Wet Deposition: No.
• Preconfigure: Select I131g (built-in gaseous I-131 example; auto-loads realistic parameters like Vd ~0.006 m/s, molecular weight, Henry's law constants).
• Or manually: Set Vel(m/s) to 0.01 (1 cm/s, tutorial value for strong test).
• Leave other fields default/zero unless needed.
• Click green Save → close window.

3. Add Ground Deposition Level to Concentration Grid
• In the same Pollutant, Concentration Grid, and Deposition setup window:
• Under Grids: Num=1 → click radio for Grid 1 (or double-click/label) → opens Definition of Concentration Grid 1.
• In Grid Definition window:
• Num of vertical levels: Change from 1 to 2.
• Height of levels(M Agl): Change to 0 100 (space-separated; 0 first for deposition accumulation, 100 for air concentration layer).
• Optional: Update Center of Lat and Lon to match your source (e.g., 40.0 -90.0).
• Keep spacing/span reasonable (e.g., 0.05 deg, 30 deg span).
• Output grid file name: Keep cdump or change.
• Click green Save → close.

4. Run the Model
• Back in main Concentration Setup window → Save.
• Click Run Model (or equivalent button to execute HYSPLIT).
• Wait for completion → open the MESSAGE file in your working directory (text file named MESSAGE):
• Note the final total mass (near end, often in a NOTICE or summary line).
• Compare to initial emitted mass (early in file or from your emission setup: rate × duration).
• Look for vertical mass distribution tables (e.g., %Mass by height layer) — reduced low-level % indicates dry removal to ground.
• Compute % mass lost = (initial - final) / initial × 100. Tutorial expects ~10-14% for Vd=0.01 m/s over longer runs; shorter runs or lower Vd (like 0.006) show less.
• This confirms dry deposition occurred (mass removed from atmosphere).

5. Display the Results (Air Concentration + Deposition Footprint)
• Go to Display → Concentration Contours (opens your Concentration Display window).
• Key settings:
• Input File: cdump (or your output name).
• Select Pollutant: All or your species (e.g., I131 / II131).
• Vertical Display: Show Each Level.
• From Bottom Level: 0 (deposition/surface).
• Through Top Level: 100 (air layer).
• Deposition Multiplier: Select Total (shows cumulative/total deposited mass over entire run; critical for seeing the full footprint instead of incremental amounts).
• Keep numeric field 1.0 (unless scaling units).
• Concentration Multiplier: 1.0.
• Uncheck Exposure if checked.
• Contour drawing options: Dyn-Exp (dynamic exponential; best for plumes).
• Label Source Rings: On (shows distance rings around source; set Number=4, Dist=100 km, Center to your source lat/lon).
• Output File: e.g., dry_depo_plot (unique name).
• View On: Checked.


• Click green Execute Display.
• What you'll see (sequence through frames):
• Air concentration frames (at 100 m level): Reduced plume due to deposition loss.
• Final/cumulative frame (level 0 with Total): Colored deposition footprint on ground (accumulated mass deposited as plume passed).
• If blank: Confirm level 0 in grid, Vd > 0, re-run if needed.

11.2 Dry Deposition of Gases.