Supplementary Information for
Characterizing the annual cycle of African dust transport to the Caribbean Basin and
South America and its impact on air quality and the environment.
Joseph M. Prospero1, François-Xavier Collard2, Jack Molinié3, and Alexis Jeannot2
1
Rosentiel School of Marine and Atmospheric Science, University of Miami
Miami, Fl, 33149-1098, jprospero@rsmas.miami.edu
2
Observatoire Regional de l’Air, 97345 Cayenne cedex,
3
Université des Antilles et de la Guyane, Guadeloupe,
Global Biogeochemical Cycles, 2014
Introduction:
This Auxiliary Material consists of two sections.
1: Assessing the Impact of Local Sources:
2: HYSPLIT Ensemble Back Trajectories:
1: Assessing the Impact of Local Sources
Because the monitoring sites are located proximate to urban areas, there is concern that the
measurements might be significantly impacted by local sources. To address this issue,
measurements were made in campaigns that were specifically intended to compare
measurements made at sites outside the Cayenne urban area to assess the degree to which the
PM10 made in central Cayenne might have been impacted by local urban sources. To this end we
show PM10 data collected at Cayenne along with data collected concurrently using identical
TEOM instruments at two non-urban sites.
fs01: Figure S1: Concurrent measurements of PM10 at Cayenne and Sinnamary, French Guiana,
in 2009. Sinnamary (5.376N, 52.957W) is a small village (area population 3,200) located 85 km
NW of Cayenne and 7 km from the coast. Sinnamary measurements were made in four periods
in 2009: 1) in May during the end of the dust season; 2) at the end of June and beginning of July
during the annual low point in PM concentrations; 3) in August during the period when transport
form Brazilian is active [Prospero et al., 1981]; and 4) around 1 November just before the
beginning of the next African dust cycle, The close tacking of the measurements suggests that
local sources do not contribute substantially to PM10. It is particularly notable that the
measurements in Sinnamary during the annual dust cycle minimum, around 1 July, closely track
those in Cayenne thus confirming that even at this time of year local sources are not significant.
Similarly the close tracking over the August period supports our contention that the aerosols
during this period are advected from distant sources to the southeast of French Guiana, most
likely from northeastern Brazil [Prospero et al., 1981].
fs02: Figure S2: Concurrent measurements of PM10 made at Cayenne and at Matoury during two
campaigns in 2009. Matoury is a residential suburb 10 km south of Cayenne. The monitoring
site at Matoury is located near Félix Eboué Airport, the main airport of Cayenne. a.)
Measurements made during the end of the dust season, late May-June 2009. Three large dust
events occurred during this period. The highs and lows tracked closely during the first two
events; the lows in the third event were somewhat higher in Cayenne than at Matoury. b.)
Measurements made during the beginning of the dust season in January 2010. Measurements
tracked closely especially over the two dust events in late January. These two examples suggest
that PM10 is almost completely controlled by advected aerosol.
2: HYSPLIT Ensemble Back-Trajectories:
The calculation of back trajectories is subject to many uncertainties because of errors in input
meteorological fields and in the numerical methods used in the calculations. To better
characterize the uncertainties associated with a single trajectory and the sensitivity to changes in
the fields, we ran HYSPLIT in ensemble mode which generates multiple trajectories from a
single meteorological field (Draxler, 2003; Draxler and Rolph, 2003). Each ensemble member is
computed from the same location, but during the initial calculation the meteorological grid is
offset by a fixed grid factor (one grid meteorological grid point in the horizontal and 0.01 sigma
units in the vertical). For each selected start time, this produces 27 members for all-possible
offsets in X,Y, and Z.
fs03: Figure S3: HYSPLIT ensemble plots: 26 April 2009 – 23 June 2009. Ensemble BTs were
calculated for each day shown in Figure 6 in the main text. Each row is one day (e.g., top row is
26 April 2009, 1800 UTC). In each row the Barbados BTs are plotted on the left and the
Cayenne BTs on the right. The symbols along the BT paths and altitude profiles mark 24 hour
intervals. Note that in many examples the ensemble BTs are closely bunched over the path across
the Atlantic. However once the BTs cross the coast of west Africa they tend to diverge widely. In
contrast, the altitude paths tend to be more widely dispersed over the Atlantic and even more
greatly over Africa.
References:
Draxler, R.R. 2003, Evaluation of an ensemble dispersion calculation, Journal of Applied
Meteorology, 42, 308-317.
Draxler, R. R., and G. D. Rolph (2003), HYSPLIT4 (Hybrid Single-Particle Lagrangian
Integrated Trajectory) Model, NOAA Air Resources Laboratory,
Silver Spring, Md. [Available at http://ready.arl.noaa.gov/HYSPLIT.php.]
Prospero, J. M., R. A. Glaccum, and R. T. Nees, 1981: Atmospheric transport of soil dust from
Africa to South America. Nature, 289, 570-572.