Appendix F

Analysis Using HYSPLIT Trajectories for Days with Largest Contribution to Haze by 

Various Species of Particles

Contents of Appendix F

Discussion of trajectories and results

Summary of trajectories (Table 3-4 from the FIP)

Maps of trajectories

Procedure used for trajectories

Discussion of trajectories and results

Where do the particles come from that affect visibility in the Virgin Islands National 

Park? The HYSPLIT model plots paths taken by particles blown by the wind through the air. 

The HYSPLIT model has historical meteorological data, to see where the air traveled enroute to 

the IMPROVE monitor, located on St. John, near Cruz Bay, on days when visibility was worst as 

measured by the samples taken by the IMPROVE monitor. Explorers traveling by balloon use

trajectory models to find the most favorable winds to get them where they want to go. 

By calculating trajectories, we can test our suppositions about where the various kinds of 

particles come from. For example, if the major cause of obstruction to visibility on a given day

is due to sulfates or nitrates, and sulfates and nitrates are products of combustion, trajectories on 

those days would be likely to come through areas with lots of sources of combustion on the way

to affecting visibility at the IMPROVE site.

HYSPLIT model uses weather data measured every three hours at the surface and twice a 

day aloft. These data are converted to a grid of values of wind direction and speed and other

weather factors for each hour of the day. 

The user specifies the starting point (in our case, the IMPROVE monitoring site on St. 

John), how long to run the model (2 weeks) and the height above ground at the monitoring site. 

We used the model to go backwards from the IMPROVE site to see where the air came from.

We started at three different heights above the monitoring site within the well-mixed tropical 

surface layer, since tropical air is well mixed over land at these heights. But wind can change 

direction at different altitudes and give different trajectories, even on the same day.

Since the trade winds mostly blow from east to west across the Virgin Islands, it is not 

surprising that when the winds are traced backwards from the sampling site on the western end 

of St. John, the path that the air takes almost always passes eastward over the island of St. John. 

Many trajectories pass over neighboring islands like Antigua and St. Martin. Some trajectories 

pass over the British Virgin Islands, located to the northeast of St. John. 

However, as the summary of the paths of the air parcels show (see the enclosed table) 

there is not any particular pattern where days with the highest amounts of light-scattering 

particles have trajectories that commonly pass through one or more of these likely sources of 

human air pollution. For example, only one of the days with high levels of haze that may be from 

combustion has trajectories that pass over St. Croix, home to a major industrial center. These 

trajectories show that even on days when visibility is reduced due to sulfates, nitrates, and carbon 

(likely suspects from sources of combustion), the air affecting the park usually does not pass 

over St. Croix, St. Thomas, or Puerto Rico. 

More often, days with high concentrations of fine soil or coarse particulates in the 

atmosphere occur when air travels from Africa’s Sahara Desert. For example, Figure 1 shows a 
set of backward trajectories originating at the Virgin Islands National park for 100 (red), 500

(blue), and 1,000 (green) meters above ground level for September 26, 2002, which is typical of 

days with high visibility impairment due to fine soils. This illustrates how a significant cause of 

reduced visibility in the Virgin Islands National Park is dust transported from the Sahara Desert, 

located over 5,000 miles away in Africa. The Virgin Islands can also be affected by other various 

natural sources, such as sulfate produced by plankton in the ocean, and ash from the Montserrat 

Volcano located over 200 miles away to the southeast. The effects of these natural sources on 

visibility can be very noticeable on some days, especially because there are not as many 

anthropogenic sources of pollution in the Islands in comparison with the more urban areas of the 

continental United States.

.

Figure 1. HYSPLIT trajectories for a low visibility day with high concentrations of fine soil.

References

Draxler, R.R. and Rolph, G.D., 2012. HYSPLIT (HYbrid Single-Particle Lagrangian Integrated 

Trajectory) Model access via NOAA ARL READY Website 

(http://ready.arl.noaa.gov/HYSPLIT.php). NOAA Air Resources Laboratory, Silver Spring, MD.

Rolph, G.D., 2012. Real-time Environmental Applications and Display sYstem (READY) Website 

(http://ready.arl.noaa.gov). NOAA Air Resources Laboratory, Silver Spring, MD. 

We gratefully acknowledge the NOAA Air Resources Laboratory (ARL) for the provision of the 

HYSPLIT transport and dispersion model via the READY website 

(http://ready.arl.noaa.gov)used in this analysis. 

The trajectories were run by Edward Finfer of EPA Region 2, Air Programs Branch and 

reviewed by Henry Feingersh, also from EPA-R2-APB
The following maps are HYSPLIT trajectories output as.kmz files and plotted on Google Earth.

Table Error! No text of specified style in document.3-1: Summary of Trajectory Analyses for Top Four Days with the 

Highest Visibility Impairment for Each Species 2000 – 2004

Species Total 

Light 

Extinct

-ion 

(bext)

Date Source Region (Height of Trajectory in Meters Above Ground Level)

Local Regional Long-Distance

All 

Aerosols

Combined

79.5 06 23 2004 St. John (100, 500) Anguilla (100) NW Africa (500, 1000)

77.4 08 01 2004 St. John (100, 500, 1000) None NW Africa (1000)

71.8 07 08 2004 St. John (100, 500, 1000) Anguila (500) Central Africa (1000)

71.1 08 01 2003 St. John (100, 500) Anguila (100) 

St. Martin (500)

African Coast (1000)

Fine Soil 19.9 09 26 2002 None None Central Africa (500, 1000)

17.9 08 01 2004 St. John (100, 500, 1000) None NW Africa (1000)

17.3 08 03 2002 None Guadeloupe (100) Central Africa (1000)

16.9 06 14 2004 St. John (1000) Guadeloupe (100, 500) Central Africa (1000)

Sea Salt 24.2 03 07 2003 St. John (100, 500, 1000) None None

21.8 03 10 2003 St. John (100) Anguila (100) None

18.9 08 01 2003 St. John (100, 500) Anguila (100) 

St. Martin (500)

African Coast (1000)

17.9 02 12 2001 St. John (100, 500, 1000) None None

Sulfate 42.0 04 24 2003 St. John (100) Puerto Rico (1000) None

34.9 11 21 2001 St. Thomas (100) Puerto Rico (100, 500) 

Dominican Rep. (1000)

Florida (500)

26.8 08 03 2002 None Guadeloupe (100) Central Africa (1000)

26.6 02 27 2004 None Montserrat (500) Western U.S. (1000)

Nitrate 5.2 05 09 2003 St. John (100, 500, 1000) Anguila (500)

Barbuda (1000)

None

4.8 11 15 2001 None St. Martin (100)

Barbuda (500)

Canada (100, 500, 1000)

4.52 08 01 2003 St. John (100, 500) Anguila (100) 

St. Martin (500)

African Coast (1000)

4.52 05 21 2003 Puerto Rico (500, 1000) Dominica (100)

Guadeloupe (500)

None

Elemental 

Carbon

15.5 09 05 2002 St. John (500, 1000)

BVI (100)

None Central Africa (1000)

African Coast (500)

14.0 01 08 2002 None St. Martin (100) Mideast U.S. (100)

Mexico, Florida (500, 1000)

13.3 08 13 2004 None St. Martin (100, 500) None

10.3 11 20 2003 None BVI (100, 500) Canada, N.E. U.S. (100)

Organic 

Carbon

18.4 01 08 2002 None St. Martin (100) Mideast U.S. (100)

Mexico, Florida (500, 1000)

17.2 09 05 2002 St. John (500, 1000)

BVI (100)

None Central Africa (1000)

African Coast (500)

7.09 10 26 2002 St. John (100, 500, 1000) None Central Africa (1000)

7.05 08 13 2004 None St. Martin (100, 500) None

Coarse 

PM

34.4 09 26 2002 None None Central Africa (500, 1000)

33.4 06 23 2004 St. John (100, 500) Anguilla (100) NW Africa (500, 1000)

30.5 08 08 2001 St. John (100, 500, 1000) BVI (100, 500, 1000) W Africa (100, 500, 1000)

28.8 07 14 2003 St. John (500, 1000) BVI (100, 500) None

Dates in italics are days when it was a top four date for more than one species of particles.
Figure 2. Trajectories with time and dates for worst haze days 2000-2004 for all types of particles. See Table 3-4 for list of 

days and type of particle.
Figure 3 Same as Figure 2 – trajectories for worst haze days for all types of particles - but a wider view, 

including Puerto Rico and other islands in the area of the Virgin Islands

Figure 4. Global view of trajectories in Figure 2 for worst haze days 2000-2004 for all types of particles.
Figure 5. Trajectories for worst visibility days due to sulfate, 2000-2004

Figure 6. Global view of trajectories for worst visibility days due to sulfate, 2000-2004
Procedure Used for Trajectories

Trajectories for VI haze plan for selected IMPROVE monitoring days 2001- 2004. 24 hour 

(midnight to midnight) particulate matter filter sampler using READY HySplit trajectories 

program, Internet version, click on :

http://ready.arl.noaa.gov/hysplit-bin/trajtype.pl?runtype=archive .

Instructions: 

Click on the box under: First, select the meteorologcal data: Select: REANALYSIS met data; 

Enter latitude: +18.336, and longitude: -64.796

Click: Continue

Select Select the reanalysis File

For the month and year for the date of the trajectory we want, 

e.g., RP200205 is year 2002, month 05 (May 2002).

Click: Next

Trajectory direction: backward 

Vertical Motion: model vertical velocity. 

Start time (UTC): Fill in year month and day from the data and hour = 18 (for 1800 UTC, which 

is 2pm time in the Virgin Islands).

Total run time (hours): 515

Start a new trajectory every: should be 0

Start 1 latitude (degrees): should already be 18.336

Start 1 longitude (degrees): should already be -64.796

Leave Start 2 and 3 blank

Level 1 height: 100 (meters)

Level 2 height: 500

Level 3 height: 1000

Display options:

Don’t change any defaults, except for: GIS output? Click: Google Earth (kmz)

Click: Request trajectory

Wait for graphics files. When they are ready, they will look something like this:

HYSPLIT MODEL RESULTS FOR JOB NUMBER 33054

Model

Status: 

Wed May 5 14:13:22 EDT 2010

The model and graphics are now complete.

Finished generating graphics for job 33054.

 adding: greenball.png (deflated 1%)

 adding: redball.png (deflated 0%)

 adding: blueball.png (deflated 0%)
RESULTS

Click on text link to view images in a new window.

GIF Plots Google Earth Plots

Trajectories GIF

KMZ

Right click on gif and save in directory with time and date in file name

Right click on kmz and save in directory with time and date in file name

For example, this example can have a file name with the year, month, day, hour, 

e.g., 2002 05 05 18.gif

and 2002 05 05 18.kmz

Save the trajectory plots.

The gif version should look like this:

Additional runs can be made for multiple trajectories by following these directions:
Click on the box under: First, select the meteorologcal data: Select: REANALYSIS met data; 

Enter latitude: +18.336, and longitude: -64.796

Click: Continue

Select Select the reanalysis File

For the month and year for the date of the trajectory we want, 

Click: Next

Trajectory direction: backward 

Vertical Motion: model vertical velocity. 

Start time (UTC): Fill in year month and day from the data and hour = 18 (for 1800 UTC, which 

is 2pm time in the Virgin Islands). But for the day, fill in the day *plus 1 day*, e.g., day in this 

case would be 06 instead of 05. Enter a time of 03 .

Start a new trajectory every:

3 hrs Maximum number of trajectories: 8

Total run time (hours): 515

Start a new trajectory every: should be 0

Start 1 latitude (degrees): should already be 18.336

Start 1 longitude (degrees): should already be -64.796

Leave Start 2 and 3 blank

Level 1 height: 100 (meters)

Level 2 height: blank

Level 3 height: blank

Display options:

Don’t change any defaults, except for: GIS output? Click: Google Earth (kmz)

Click: Request trajectory

Wait for graphics files. 

This file should look like the graphic on the next page.

Then save the file as year date height

e.g., 2002 05 05 100m.gif

and the kmz file as 2002 05 05 100m.kmz

Then go back and run the same information, changing only the Level 1` height to 500 and after you get the

maps for that run, change the Level 1 height to 1000 and get the maps for that run.