Vol.2, No.10, 1119-1129 (2010) Natural Science
Copyright © 2010 SciRes. OPEN ACCESS
Origin and SEM analysis of aerosols in the high
mountain of Tenerife (Canary Islands)
Juan D. Delgado1,2*, Omaira E. García3, Ana M. Díaz3, Juan P. Díaz3, Francisco J. Expósito3,
Emilio Cuevas4, Xavier Querol5, Andrés Alastuey5, Sonia Castillo5
1Área de Ecología, Departamento de Sistemas Físicos, Químicos y Naturales, Universidad Pablo de Olavide, Seville, Spain;
*Corresponding Author: jddelgar@upo.es;
2Instituto Universitario de Enfermedades Tropicales y Salud Pública de Canarias, La Laguna, Tenerife, Canary Islands, Spain;
3Departamento de Física Básica, Universidad de La Laguna, E-38206 La Laguna, Tenerife, Canary Islands, Spain;
4Izaña Observatory, Instituto Nacional de Meteorología, INM, Santa Cruz de Tenerife, Canary Islands, Spain;
5Institute of Environmental Assessment and Water Research (IDAEA), CSIC, Barcelona, Spain.
Received 18 May 2010; revised 21 June 2010; accepted 24 June 2010.
Focusing on aerosolized matter of relevance to
respiratory health, a major public health issue
worldwide, we studied mineral and biological
aerosol (bioaerosol) composition (TSP and PM2.5)
and geographical origins during dust intrusions
in the Canary Islands. Seven days’ backward tra-
jectories were assessed daily during March
2004 with the ends of back trajectories being the
sampling station of Izaña (high mountain, 2360
m a.s.l. at the Cañadas del Teide National Park,
Tenerife island), a free troposphere site allowing
characterization of dust with low influence of
other pollutant sources. Scanning electron mi-
croscopy (SEM) was used to survey major types
of airborne particles in the dust plumes. Control,
non-intrusion conditions correspond to Atlantic
oceanic middle troposphere (OMT) air masses.
Of the 14 samples taken, 1 corresponded to a
control (clear atmosphere conditions), and the
remaining 13 to dust intrusions, with the fol-
lowing sources: African Dust; EAM: mixture of
Europe, Africa and Oceanic; MaA: maritime
aerosols. Of the air masses, 79% were directly
transported to the islands from Africa, and an
increase of African dust events was detected
when comparing with a 52-year previous data
sequence. Quartz microcristals and aggregates
of quartz and platy clay were the dominant mi-
nerals identified, with marine salt and gypsum
also present. Freshwater diatom tests (from two
Aulacoseira species) represented the most im-
portant biogenic aerosols, although fungi and
pollen were also detected. The diverse and com-
plex mixture of respirable particles in large
quantities in airborne dust, especially from near-
by Sahara and from the Sahelian region, is of
maximum interest for airway pathology in the
Canaries, including the highly visited highlands
in Tenerife.
Keywords: Allergens; Bioaerosols; Diatoms; High
altitude; Desert dust intrusion; Public health;
Scanning electron microscopy
The dispersal of abiotic and biological aerosols (bioa-
erosols), has a growing interest in interdisciplinary re-
search comprising epidemiology, public health and at-
mospheric physics. This is due to the great capacity of
air masses to transport both viable organisms and inor-
ganic dust to remote areas, where they transform local
tropospheric conditions [1] and may affect human health
[2]. The cell-carrying capacity of wind, long-range and
high frequency transport of dust masses, aggravate the
effects of seasonal peaks in local allergens through addi-
tive and synergic effects. The transport of dust might
involve carrying up to 10.000 bacterial cells per gram of
soil from some desert areas [3]. For example, diatoms
are a large fraction of dust carried from fresh waters of
the Saharo-Sahelian areas and Eurasia to remote areas
such as the Caribbean [4]. Charles Darwin, on his 1845
voyage aboard the surveying ship H.M.S. Beagle, col-
lected African dust in the Atlantic and microscopically
detected the occurrence of diatoms in the dust. This
same historic dust has been recently analyzed to find at
least 16 different viable bacterial lineages and 2 fungal
isolates [5].
Although the global amount of species of airborne
pathogens is not so far clearly defined, several hundreds
J. D. Delgado et al. / Natural Science 2 (2010) 1119-1129
Copyright © 2010 SciRes. OPEN ACCESS
of bacterial lineages, fungi and viruses can be involved
in allergy, asthma and pulmonary affections, and air-
borne dust is a vehicle for them [6-10]. Inhaled atmos-
pheric aerosols of any origin can be associated with a
number of diseases and disorders, namely allergic air-
ways disease (or asthma), rhinitis and rhinosinusitis, al-
veolitis or allergic parenchymal disease, airways or pa-
renchymal infections, atypical thoracic pain, anxiety dis-
orders, cardiopathy, and meningitis, among others [11-14].
The Canary Islands lay 96 km off the west of the lar-
gest dust source on Earth, the Sahara desert (> 9 million
square kilometres), being comprised within the “dust-
belt”, where the atmospheric dust concentration is inhe-
rently very high [15]. Dust transport to the Canaries causes
several-fold increase over the standard levels of particu-
late matter over the islands [1,16-20]. Although studies
relating desert dust to “airborne” diseases in the Canary
Islands are scant, dust events reach the archipelago with
a high frequency, being associated with augmented pre-
valence, morbidity and mortality [12]. There are prece-
dents in other regions, such as the Caribbean Sea where
increase of frequency in African dust episodes reaching
Barbados were associated to a seventeen-fold increase in
asthma between 1973 and 1996 [21-23]. In Gran Canaria
and Tenerife, type and frequency of asthma symptoms
have been analyzed in a large population sample, and
climatic conditions have been invoked to explain high
prevalences [24].
In this paper we study aerosols from African dust in-
trusions at a high altitude ecosystem in Tenerife, Ca-
narian archipelago. Specific health effects of minero-
genic dust and bioaerosols have not been studied so far
in the Canary Islands, and this task is difficult to ap-
proach without recognizing the type of particles in-
volved. We thus aimed to identify and survey, through
scanning electronic microscopy (SEM) analysis, the
biological and mineral aerosol particles transported with
dust during intrusions of African air masses and from
other origins to the Canary Islands. Imaging characteri-
zation of dust particles could give us explicit information
on aerosol types in relation with complementary data on
origin and travelling time of air masses. We related the
dust events with the air-mass origin, tracing back the dust
trajectories to assess source areas. Our primary concern
was on aerosolized particles with a potential interest in
public health that are transported with dust plumes from
Africa to the Canary Islands.
2.1. Study Area
We studied air samples searching for biogenic parti-
cles (bioaerosols) during a non-intrusion episode (“clean
atmosphere”) and during dust invasions to Tenerife, the
largest and more densely populated and visited island of
this group (Table 1). Our sampling was focused on the
Table 1. Characteristics of air samples from filters taken at the high mountain station of Izaña in Tenerife.
Particle sampler
Hour (GMT) and initial
sampling date
Hour (GMT) and
final sampling date
Cycle volume
African dust
outbreaks Initial sampling Final sampling
PM2.5 14:44 03/03/04 14:50 04/03/04 731 + EAM EAM
PM2.5 14:58 04/03/04 15:40 05/03/04 506 + EAM EAM
PM2.5 12:22 17/03/04 12:26 18/03/04 731 + AfD AfD
PM2.5 11:05 22/03/04 11:40 23/03/04 733 + AfD AfD
PM2.5 10:12 04/04/04 15:35 05/04/04 732 + MaA MaA
TSP 15:48 03/03/04 15:55 04/03/04 732 + EAM EAM
TSP 16:10 04/03/04 16:20 05/03/04 731 + EAM EAM
TSP 16:30 05/03/04 16:45 06/03/04 731 + EAM EAM
TSP 12:26 11/03/04 15:10 12/03/04 731 (control) OMT OMT
TSP 12:13 17/03/04 12:17 18/03/04 731 + AfD AfD
TSP 12:23 18/03/04 13:30 19/03/04 732 + AfD EAM
TSP 11:00 22/03/04 11:35 23/03/04 731 + AfD AfD
TSP 11:45 23/03/04 12:20 24/03/04 731 + AfD AfD
TSP 10:05 04/04/04 13:40 05/04/04 732 + MaA MaA
Trajectory codes: OMT: Atlantic Oceanic Middle Troposphere; AfD: African Dust; EAM: mixture of Europe, Africa and Oceanic origins; MaA: maritime aero-
J. D. Delgado et al. / Natural Science 2 (2010) 1119-1129
Copyright © 2010 SciRes. OPEN ACCESS
high mountain scrub, at the Teide National Park (free
troposphere, over the stable inversion layer, which is
found between 1000-1500 m), at the facilities of the In-
stituto Nacional de Meteorología (Izaña Observatory,
16º29'58" W; 28º18'32" N; 2360 m a.s.l.) (Figure 1).
The Izaña site is located above a sharp temperature
inversion between 500 and 1500 m, thus remaining rela-
tively apart from the contamination foci of the low areas
and human settlements [25]. At Izaña, the characteriza-
tion of African dust is possible with low interference of
other pollutant sources [26]. The dust transport is str-
ongly seasonal, occurring near the surface in the cold
season (October to March) and above two kilometres
altitude in the warm season (April to September) [27,28].
We centred the sampling effort in March-April 2004.
Annual distribution of particulate matter at low areas in
the Canary Islands peaks in winter and shows a mini-
mum in summer, whereas in the Tenerife high mountain,
the maximum dust incomes occur in summer. Neverthe-
less dust episodes are also commonly detected in spring-
time in both levels [19,27,28]).
2.2. Dust Trajectories and Origins
To assess the origin of the aerosols, seven days back-
ward trajectories were calculated daily at 00 and 12 UTC
during March 2004 with HYSPLIT-4 model (Draxler
and Hess, 1997 in [27]). The end point of the back tra-
jectories was the Izaña station. Physical-chemical aero-
sol properties can be related with the origin and trajec-
tory of the aerosol-laden air masses. Díaz [27] and Díaz
et al. [28] developed a methodology to characterize the
source-transport paths of the aerosol over this region
using multivariate clustering analysis. The back trajecto-
ries classification is based on the contribution of the
main aerosol sources, considering the geographical re-
gions, the residence time in these sectors and the altitude
of the air mass during the evolution towards the island.
With this technique, clusters of back trajectories can be
found for different levels of transport and origins of the
air masses [28].
2.3. Dust SEM Analysis
TSP (Total Suspended Particles) and PM2.5 (Particu-
late Matter with 2.5 micrometers diameter or smaller)
were sampled simultaneously on quartz glass filters (Sch-
leicher and Schuell, QF20), with high volume samplers
MCV CAV-A / M (30 m3/h). Samplers operated for 24 h
periods from 03 / 03 / 04 until 05 / 04 / 04, and com-
pleted 14 samples (Table 1). We separated part of the
filters for scanning electron microscope (SEM) anal-
ysis. A small section (< 1 cm2) of each filter was cut and
glued onto an aluminium stub and processed for SEM.
Complementarily, another section of the filter was gently
pressed on an adhesive carbon conductive tab to transfer
the filter content to the preparation, then the tab was
glued to the stub and processed for SEM. Preparations
Natio nal
Figure 1. Study area and sampling stations.
J. D. Delgado et al. / Natural Science 2 (2010) 1119-1129
Copyright © 2010 SciRes. OPEN ACCESS
were observed and photographed in a JEOL JSM 6300
electron microscope. We resolved the elemental compo-
sition of some particles with X-ray electron probe mi-
croanalysis (EDX) (OXFORD 6699) of selected SEM
samples. The system operated at 20 kV (operation range:
0.2-30 kV) with a maximum resolution of 3.5 nm.
3.1. Dust Trajectories and Origins
Clusters of back trajectories found were: 1) represent-
tative of Atlantic oceanic middle troposphere (OMT); 2)
air masses originated in the African continent (AfD); 3)
mixture of aerosols from at least two of these sources:
Europe, Africa and Ocean (EAM); 4) air masses with
high load of maritime aerosols (MaA). The average fre-
quencies of occurrence of these clusters on March over a
52 year period (1948-2004) were 17% AfD, 24% EAM,
40% OMT and 19% MaA.
Mean altitude for trajectories ending at Izaña was
2970.85 m (range: 0-8119.5 m) in March 2004. The back
trajectories analysis for Tenerife for that month showed
that air masses were 30% AfD, 24% EAM, 24% OMT
and 22% MaA. These values revealed an increase in fre-
quency of African dust events (cluster AfD) of 13% at
the high mountain site compared with the average value
of the 52-year period. In particular, of the 14 samples
obtained at Izaña (Table 1), 13 corresponded to mineral
dust conditions, where the 79% of the air masses were
directly transported from the African continent (43%
AfD and 36% EAM), whereas the remaining two repre-
sent maritime air masses with presence of dust particles.
This last situation is observed most likely during the
spring-summer period at Izaña [28], where the air masses
cross areas with a high concentration of dust due to a
Sahara-Sahel outbreak occurred in previous days. As
exemplified in Figure 2 (upper panel), the air mass in
cluster AfD progressed at low altitudes while crossing
the eastern Sahara desert (particularly between 0 and 15º
E) and then gained altitude approaching the Atlas range,
finally reaching the end point in the Tenerife high moun-
tain at 2360 m. Furthermore, given that a 24 h sampling
schedule was applied, the possibility of ascending air
masses transporting coastal material up to the summit at
Izaña station can not be disregarded [26].
3.2. SEM Survey of Dust Particulate Matter
In our SEM samples, most abiotic and biological or
biogenic particles are within the respirable size range.
Aerosols presenting a wide size range (including PM2.5
and PM10) were quartz and clay grains, gypsum rods and
halite. Crustal aerosols appeared clustered, which increa-
sed average lateral dimension of particles. The main bio-
-80 -60-40 -20 020
-80 -60 -40 -20020
Altitude (Km)
Figure 2. Values of the TOMS AI (Total Ozone Mapping Spec-
trometer Aerosol Index) for a back trajectory of 24 / 03 / 2004
(black line, below graphic) of African mineral dust estimated
for Izaña (Tenerife, Canary Islands). The TOMS aerosol index
is a relative measure of the amount of aerosol particles absorb-
ing radiation in the atmosphere. The vertical altitude- longitude
cross section of the trajectory is shown in the upper panel
(maximum at ca. 2400 m a.s.l.). The white arrow points the
geographic evolution of the air mass from left to right. The
colour scale is adimensional and depicts the TOMS AI.
aerosols found here (diatoms) belong to the PM10 frac-
tion, although a large amount of fragmented thecae were
within the PM2.5 class; pollen grains and one fungal co-
nidium were within PM10.
3.3. Aerosols of Biotic Origin
We made only an overview of major aerosol types
transported with dust to the Canaries, and we did not
quantify the concentration of airborne species. The most
abundant biological remains identified in our SEM sam-
ples for African dust episodes were diatom siliceous tests
(Figure 3). Two species of the genus Aulacoseira Th-
waites (1848) (formerly Melosira), were identified: A.
granulata (Ehrenb.) Simonsen 1979 and A. islandica (O.
Müller) Simonsen (Bacillariophyta). Apart from diatom
remains, other biogenic material was difficult to observe
in SEM preparations, where the mineral fraction domi-
nated. We identified only one fungal taxon, most proba-
bly Alternaria sp., as determined from a clavate conidium,
showing the loculi under an irregular surface (Figure 3
Pollen grains were found by SEM but species could
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Figure 3. SEM photographs of TSP and PM2.5, biogenic particulate matter or bioaerosols identified in dust
filters from Tenerife (Canary Islands) during African dust intrusions. All samples from Las Cañadas (high
mountain site), excepting F (Santa Cruz, coastal city). (A): Typically club-shaped Conidium of ascomycotan
fungi (Alternaria sp., a cause of allergic fungal sinusitis). (B)-(D): Siliceous tests of freshwater diatoms ((B)
and (C): Aulacoseira granulata; (D): A. islandica), heavily eroded and worn due to the transport process.
(E): Conglomerate of diatom test remains (presumably Aulacoseira spp.) with platy clay particles. (F): un-
determined pollen grain, cross-section, containing mineral particles (Santa Cruz). (G): pollen grain, undeter-
mined species. (H): fragmentary spicule-like particle (inset: magnification), origin (either abiotic or bio-
logical) and composition uncertain.
J. D. Delgado et al. / Natural Science 2 (2010) 1119-1129
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not be assigned (Figure 3(G)). Pollen was very rare in
filters, which operated during the early spring season
when flowering period was not at its peak in the Tenerife
high mountain. We failed to identify bacterial cells in
filter preparations examined with SEM.
3.4. Aerosols of Abiotic Origin
Filters from the control day (“clean troposphere”) show-
ed a very different aspect when compared with filters
from dust events (Figures 4(A),4(B)), the latter being con-
cealed with a dense mineral-biomineral matrix (Figure
4(C)). The abiotic particulate aerosols identified indivi-
dually included clay grades and quartz microcristals (iso-
lated or aggregated) of crustal origin (from AfD cluster),
and gypsum rods (CaSO4). Halite, cubic and cube-octa-
hedra crystals of sea salt (NaCl) were obtained from the
OMT cluster correspondent to clear atmospheric condi-
tions and incidence of marine aerosol reaching the high
mountain area (compare with [26]).
Quartz (SiO2) microcristals (particles from < 10 µm to
< 2 µm) formed the dominant or background material in
our filters during dust intrusions (Figure 4). Aerosols
transported from the Sahara desert are enriched in clay
material due to a high residence time in atmosphere
caused by a smaller particle size and laminar habit; these
clay grade grains are transported as particles of silt size
forming aggregates [29,30] (Figure 4).
As suggested by our filter samples from different ori-
gins, Aula co s eir a diatom thecae compound the dominant
biogenic aerosol, and quartz is the dominant mineral
fraction, which also formed up to 60% of dust material
in a study from Gran Canaria [31].
The diatoms identified are dominant taxa in fresh wa-
ters from N and NW Africa, and can be found through-
out the Palaearctic [32]. A. granulata has been recorded
in the Arctic probably transported from Siberia [33].
Both A. islandica and A. granulata are typical of eutro-
phized and alkaline waters. As far as we know, these
species have not been deemed as pathogenic to humans;
on the contrary, they are used as bioindicators of fresh-
water quality in most studies. They can be transported as
viable cells through the ocean, and their importance in
the windblown diatom fraction decrease with increasing
distance from the African continent [4]. The aeolian tran-
sport of diatoms and phytolyths from continental fresh
water deposits in the Sahara and Sahel [4,34] should be
investigated to assess relative contribution to high inci-
dence of environmental airway diseases in the Canaries.
We are not aware of detailed clinic studies relating natu-
ral (desert) diatom dust with respiratory diseases. Fur-
thermore, concentrations of airborne diatom particles from
African deserts and professional exposure to diatom dust
are not comparable [35]. Diatoms transported with the
dust plumes to the Canaries augment the overall silica
content of the aerosols, and silicosis caused by non-
crystalline forms of silica have not only occupational but
environmental etiology [36]. On the contrary, non-in-
dustrial silicosis (known as “desert lung”) has been re-
ported decades ago from autopsy of Bedouine lung tis-
sue, showing high amounts of silica dust of respirable
size [37]. More study cases of non-industrial lung or en-
vironmental silicosis, have been reported for regions ch-
ronically exposed to desert dust (i.e. Himalaya [38]).
The Tenerife highland (> 2000 m a.s.l.) is not a popu-
lated area, but it receives > 4 million visitors/year, the
most visited volcanic area of the world after Mount Fuji,
Japan. There is evidence that symptoms of asthma in
lowland patients improve with therapy of high-elevation
stays [39,40]; however, episodic but severe dust events
may imply additional health risks given the extreme
conditions at these altitudes for such long permanencies
(moderate hypoxia, high aridity of this area and increa-
sed sun radiation exposure, among other stressors). Ori-
gin and type of air mass and aerosol load can be pre-
dicted and used to establish and prevent potential inter-
actions with respiratory disease in susceptible visitors to
the island’s National Park.
Particles of different sizes have different ability to pe-
netrate the pulmonary system and reach the lung pare-
nchyma [41]. Modelling of aerosol inhalation schema-
tize the stratification of particle deposition along the
human airways depending on their aerodynamic diame-
ter [42]. Particulate matter (PM) < 10 µm (PM10) pene-
trate the tracheobronchial region; increased deposition in
the oropharynx occurs with particles larger than 6 µm,
whereas central airway deposition peaks within the 4-6
µm range. Particles like those in Figures 4(B), 4(D) or 4
(I) would be able to reach the central airways. PM be-
tween 2-4 µm (PM2.5) reach the alveolar cavities (i.e.
lung periphery), where their damage is greater due to
higher reactivity [42]. Particles like the one depicted in
Figure 4(K) seem of potential interest in this range.
Although a great proportion of diatom remains are
within or above the PM10 fraction (particulate matter 10
micrometers in diameter), thereby being potentially re-
tained by the trachea and bronchia, a great amount of
test fragments are within the PM2.5 fraction, and thus
could reach the lung alveolar system [35]. In addition,
the role of diatom thecae as carriers of particles of health
interest (e.g. bacteria, viruses, fungal or protozoan
spores or cists, pollen) can be important, since: a) these
remains co-dominate, along with quartz mineral, in
many of the dust events of North African origin, and b)
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Figure 4. SEM photographs of TSP and PM2.5, mineral aerosols of crustal, marine and anthropogenic
origin identified in dust filters from Tenerife (Canary Islands) during an African dust intrusion. (A)-
(B): two general views of a relatively clean filter with few mineral particles (without African dust)
from Izaña. (C): filters with dense platy clay microcrystals typical of a dust intrusion (Santa Cruz).
(D): Agglomeration of clay on carbon adhesive film (EDX: Si, Al, K, Ca, Fe, Na, Mg) (Izaña); 1: elon-
gate rectangles on the aggregate surface are gypsum rods (EDX: Ca, S, O). (E)-(F): clay microcristals;
1: clay aggregates; 2: flat and rounded quartz particles adhered (Izaña). (G)-(H): halite (EDX: Na, Cl),
clusters of cubic crystals from marine aerosol (Santa Cruz). (I)-(J): conglomerates of quartz clay gra-
des with diatom test fragments of laminar habit (1); (K): fibrous particle of unknown origin around
the 2 µm size range attached to filter; note the “fringed” end (1).
due to their structural complexity, large adsorption sur-
face and cavities for shelter of diverse particles, and lat-
eral dimension.
We found only a fungal remain in our dust samples.
However, fungal species linked to respiratory disease are
surprisingly frequent from desert areas [6]. Some deserts
next to urban areas behaved as differentiated sources of
Basydiomycotan fungi [43]. Kellogg et al. [10] detected
Alternaria, Cladosporium and Aspergillus in dust sam-
ples from Mali. Cladosporium was also isolated from
African dust in the Virgin Islands (Caribbean) [7]. Pros-
pero et al. [44] isolated more than 20 fungal taxa from
North African dust in Barbados, finding low percentages
of Alternaria. With Cladosporium, Alternaria is one of
the most abundant spore-forming fungi in dry and warm
regions such as the subtropical Canary Islands [6]. Al-
ternaria was also a very frequent bioaerosol in a study at
mid elevation on Tenerife [45]. In other dry climates (e.g.
Phoenix, Arizona), A. alternata and A. raphani has been
detected in PM10 from desert neighbouring urban areas
[43], and Glikson et al. [46] found that fungal spores
were predominant over other bioaerosols such as pollen
in Brisbane (Australia). We failed to find other fungal
remains through SEM, a surprising result since we ex-
pected a higher importance of this type of particles dur-
ing dust events, judging from literature. However, we
isolated and cultivated other common allergenic fungi
(Aspergillus, Penicillium and Cladosporium) which were
not detected by SEM from the same filter samples (un-
published data).
Apart from plant pathogen, Alternaria is a cosmo-
politan, saprophytic soil fungus comprising several spe-
cies pathogenic for immunocompromised hosts [47,48].
A. alternata causes environmental allergic alveolitis, and
for many authors it is the most important fungi in allergy
causation, especially in Mediterranean areas [49]. Aller-
gic fungal sinusitis is due to finely dispersed fungal spores
in air, and 56-95% percent of patients diagnosed with
chronic rhinosinusitis presented fungus in nasal secre-
tions [50,51]. We should investigate frequency and con-
centration of fungal spores in this insular region and if
causes for high prevalence of allergies in areas affected
by dust intrusions might be attributed to airborne fungal
Around 20% of the human population of the Canaries
suffers from allergy or allergy-related diseases [52]. How-
ever, prevalence of diseases such as asthma or allergies
has not been paid enough attention regarding associa-
tions with climatic factors, climate change or influence
of atmospheric phenomena such as Saharo-Sahelian dust
episodes on the archipelago [24]. The complex mixture
of particles of respirable size identified by SEM in this
study may play a role in sensitizing and thus preparing
the road for other “opportunistic” airway diseases. Proc-
esses of aerosol particles deposition and effects in the
airways depend on particle size and form, and respira-
tory conditions [35], but the mechanisms by which both
mineral aerosols and bioaerosols act in the airway pa-
thologies are poorly comprised.
In populated areas, mixtures amongst particulate mat-
ter of different origins are common during dust intru-
sions, as revealed by our SEM analysis. In many in-
stances, allergens invade the respiratory tract in or on a
different particle, and it is today clear that exposure to an
allergen on or within a carrier pollutant can substantially
enhance its allergenic potential [53,54]. Many of the
J. D. Delgado et al. / Natural Science 2 (2010) 1119-1129
Copyright © 2010 SciRes. OPEN ACCESS
aerosol types overviewed here can incorporate additional
pollutants from the atmosphere, and in case of bioaero-
sols, surface proteins can be altered and then released
into the respiratory system. Synergies between anthro-
pogenic aerosols and bioaerosols also deserve attention.
Diatom tests, quartz and gypsum fiber-like particles mix
to form aggregates, and pollen grains can transport those
and other mineral particles (Figures 4(B)-4 (F),4(J)). Im-
portant synergies between bioaerosols (mostly pollen,
fungi and soil bacteria, but perhaps also viruses) and
other atmospheric pollutants (i.e. NOx, VOCs—volatile
organic compounds—ozone, tobacco smoke) have been
reported in relation with increasing asthma prevalence in
urban areas [46]. Pollen secrete eicosanoid-like mole-
cules (i.e. leukotriene-like) which act signaling in im-
munity and inflammation, and such releasing is favoured
by contact of pollen with gases from traffic exhaust and
petrol industry [54].
The study of the origin of the air mass through back
trajectory would allow knowing the potential of remote
subtropical and tropical areas for issuing other disease
vectors in dust plumes to the Canary Islands and other
places. This tool should be integrated along with quanti-
tative and qualitative aerosol characterization in the
creation of prevention nets [12,55]. Attention should be
paid to candidate disease vectors that can be predicted,
through tracing of backward trajectories, to reach the
islands with dust intrusions in the next future. In fact,
nearly 80% of the air masses reaching the islands have a
direct North African origin. SEM analysis is useful as a
complementary tool in the morphological identification
of new particle types or combinations of particles of
interest in disease causation [56]. Moreover, exploratory
biopsy of the respiratory mucosa through SEM analysis
would prove useful in identifying PM types and linking
them as causal factors with atmospheric dust PM. Nev-
ertheless, molecular and clinical characterization of the
active substances associated to aerosols is a critical and
unavoidable step for prevention of dust mass impact on
human health [54]. In the Caribbean, relationship be-
tween asthma attendance peaks and African dust intru-
sions have previously been revealed [23]. For the Canary
Islands, where African dust intrusions exert their effects
before reaching the Caribbean, the studies dealing with
problems posed by dust intrusions on public health re-
main anecdotic, whereas effective control of dust effects
on human population is a major sanitary goal [12].
Aeolian dust reaching the high altitude areas of the
Tenerife island has a larger contribution of North African
air masses, and is formed by a structurally complex mix-
ture of biogenic and abiogenic particles, of respirable
size and contrasting morphology; we found that the dia-
tom test fraction is qualitatively relevant (along with the
dominant, background quartz fraction), whereas other
biogenic fractions such as pollen or fungi are more scar-
ce, or difficult to resolve, at least by means of SEM, and
at these elevations within the island. Increasing aridity
periods, irregular and torrential rains, changes in vegeta-
tion cover and desertification would affect the aerosol
load (both biogenic and abiogenic in origin) received by
these subtropical islands as dust intrusion events in-
crease in frequency [16,17,57].
We thank Juan Luis González Álvarez (SEGAI facilities, ULL) and
Debora Gómez for assistance with SEM. Prof. Dr. Óscar Romero (Uni-
versitaet Bremen, Germany) gently identified diatoms. We acknowledge
to the MEC (Ministry of Education and Science, Spain) and F.E.D.E.R.
founds (E.U.) for the economical support of the following projects:
CGL2005-03428-C04-02, CGL2007-66477-C02-02/CLI, CGL2008-
04740 and PI042005/033. Finally, the authors wish to express their app-
reciation to the operators of Izaña Atmospheric Observatory for their
help on running the instruments.
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