European Aerosol Conference (EAC 2016), Tours, FRA, 04-/09/2016 - 09/09/201

Benhra, A.

Losno, R.

Sarthou, Géraldine

Shelley, R.

Tito de Morais, Luis

Tymen, Georges

Zohra Boutir, F.

HAL-INSU

A case study of aerosol trace element deposition to Moroccan coastal waters

HAL-Université de Bretagne Occidentale

Tymen, G.

Tito De Morais, Luis

Archive Ouverte en Sciences de l'Information et de la Communication

HAL Id: hal-02331693
https://hal.archives-ouvertes.fr/hal-02331693
Submitted on 1 Mar 2020
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A case study of aerosol trace element deposition to
Moroccan coastal waters
R. Shelley, Géraldine Sarthou, Georges Tymen, R. Losno, Luis Tito de
Morais, A. Benhra, F. Zohra Boutir
To cite this version:
R. Shelley, Géraldine Sarthou, Georges Tymen, R. Losno, Luis Tito de Morais, et al.. A case study
of aerosol trace element deposition to Moroccan coastal waters. European Aerosol Conference (EAC
2016), Sep 2016, Tours, France. 1 p. multigr., 2016, ￿10.13140/RG.2.2.25713.89443￿. ￿hal-02331693￿
	
	
	
	
	
	
	
	
	
	
	
	
	
	
	
	
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Agadir 
Laayoune
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							A case study of aerosol trace element deposition to 
Moroccan coastal waters 
	
Rachel	Shelley*,	Géraldine	Sarthou,	Georges	Tymen*,	Rémi	Losno,	Luis	Tito	de	Morais,	Ali	Benhra,	
and	Fa>ma	Zohra	Bouthir	
	*rachel.shelley@univ-brest.fr;	georges.tymen@univ-brest.fr	
									Ra$onale	
					Aerosol	deposi>on	is	an	important	source	of	trace	elements	(TEs)	to	
the	surface	ocean.	Proximity	to	the	Sahara	Desert/Sahel	means	that	
the	North	Atlan>c	receives	some	of	the	highest	inputs	of	mineral	dust	
globally	(100-220	Tg	yr-1;	[1];	[2]).	This	input	of	TEs	contributes	to	the	
greater	efficiency	of	the	Canary	Current	Upwelling	System	rela>ve	to	
its	Pacific	counterpart	[3];	both	of	which	support	socio-economically	
important	fisheries.	However,	mineral	dust	is	just	one	component,	
human	ac>vi>es	(e.g.	fossil	fuel	burning,	agricultural	prac>ces)	also	
contribute	to	the	atmospheric	load.		
					In	the	study	region	upwelling	water	also	fuels	high	primary	
produc>on	via	the	supply	of	macro-nutrient-rich	(N,	P	and	Si)	deep	
water.	This	deep	water	may	also	be	enriched	in	TEs,	such	as	those	with	
water	column	distribu>ons	that	mirror	the	macronutrients,	e.g.		Cd	&	
P.	A	tangible	concern	for	the	fisheries	off	West	Africa	is	the	poten>al	
for	toxic	effects	at	all	levels	of	the	marine	food	web,	due	to	inputs	of	Cd	
(and	other	poten>ally	toxic	TEs).		
					The	aim	of	this	project	was	to	inves>gate	the	TE	composi>on	and	
rela>ve	levels	of	enrichment	of	aerosols	delivered	to	the	Atlan>c	coast	
of	Morocco.		
	
				Methods	
								
	
	
	
	
	
Conclusions	
§  No	strong	seasonal	paaern	in	aerosol	Al	concentra>on/dust	deposi>on,	but	tendency	towards	higher	frequency	of	dust	events	in	winter	
§  Mineral	dust	propor>onately	contributes	least	to	the	bulk	aerosol		in	Agadir,	most	in	Dakhla	
§  Dust	events	are	characterised	by	aerosols	that	originate	from	sources	in	Sahara/Sahel	
§  In	terms	of	elemental	ra>os,	Cd/Al	looks	like	other	loca>ons	in	the	region,	but	it	was	significantly	enriched	in	samples	from	all	loca>ons	&	had	liale	
to	no	mineral	dust	source	during	this	study		
§  Mineral	dust	dilutes	anthropogenic	TE	aerosols	during	dust	events	
Acknowledgements	
This	work	was	supported	by	the	Conseil	Général	
du	Finistère,	&	the	EPURE	programme.	Air	mass	
back	trajectories	were	simulated	using	the	NOAA	
HYSPLIT	model	(hap://ready.arl.noaa.gov)	
References	
[1]	Prospero	et	al.,	1996;	[2]	Kaufman	et	al.,	2005;	
[3]	Carr	et	al.,	2003;	[4]	Rudnick	and	Gao,	2003;	[5]	
Gelado-Cabellero	et	al.,	2012;	[6]	Fomba	et	al.,	
2013;	[7]	Torres-Padron	et	al.,	2002;	[8]	Guieu	et	
al.,	2010	
Three	sampling	
sites	100-800	m	
from	the	coast,	
upwind	of:	
•  Agadir	
•  Laayoune	
•  Dakhla	 Aerosol	samples	were	collected	using	a	low-volume	aerosol	sampler	manufactured	in-house:		
•  two	downward-facing,	open	face,	polycarbonate	
filter	holders	(NILU)	coupled	to	two	pumps	(NOVAIR	
NTV	0625)	&	two	volumetric	counters	(Gallus	2000)	
operated	in	series,	interfaced	with	a	laptop	
•  wind	speed	(>	0.9	m	s-1)	&	sector-controlled	in	
order	to	minimise	the	sampling	of	local	industrial	
emissions		&	sample	aerosols	delivered	from	
specific	sectors	(see	table)	
Sectors		 AGADIR	 LAAYOUNE	 DAKHLA	
MAR	 230-350°	 230-10°	 270-10°	
TER1	 10-110°	 20-120°	 30-150°	
TER2	 110-170°	 120-220°	 	
The	red	line	points	north	(0°)	for	reference		
(30.46	°N,	9.67	°W)	
(27.10	°N,	13.41	°W)	
(23.78	°N,	15.90	°W)	
Examples	of	aerosol	samples:	ler	&	
middle	=	Dakhla,	right	=	Agadir	
	
Sampling	from	March	2015-March	2016	
•  Agadir	=	44	samples	
•  Laayoune	=	66	samples	
•  Dakhla	=	56	samples	
Aerosol	concentra>ons	following:	
•  Sequen>al	digests:	(1)	5:1	HNO3:	HF,	
(2)	HNO3	in	capped,	Teflon	®	vials	at	
130	°C	
•  Solu>ons	re-dissolved	in	0.48	M	
HNO3	and	analysed	by	ICP-MS	
(Thermo,	Element	2)	
•  Posi>ve	Matrix	Factorisa>on	using	
EPA	PMF	v.5	for	source	
appor>onment	
(1)	Aerosol	Al	concentraRons,	March	2015-2016.	90%	of	data	falls	below	the	dashed	line	(2000	ng	Al	m-3).	
ConcentraRons	of	~	100-2000	ng	Al	m-3	could	be	considered	as	an	effecRve	background	concentraRon	
v  No	strong	seasonal	paaern	in	aerosol	Al	concentra>on,	but	tendency	towards	higher	frequency	of	dust	events	from	Dec-
Feb	
v  8%	Al	abundance	[4]	used	to	es>mate	total	dust	mass	for	the	year	of	study	
v  3400-67000	ng	m-3	(Agadir)	
v  350-26000	ng	m-3	(Laayoune)	
v  205-74000	ng	m-3	(Dahkla)		
v  Maximum	Al	concentra>ons	in	this	study	are	an	order	of	magnitude	lower	than	observed	on	islands	downwind	of	the	
Saharan	plume,	e.g.	Gran	Canaria	=	26200	ng	m-3	[5]	&	Sal,	Cape	Verde	=	26487	ng	m-3	[6]		
v  Despite	large	interannual	variability	in	dust	supply	[7],	this	result	was	unan>cipated.	Possibili>es	that	could	account	for	
the	difference:	
v  A	‘low	dust’	year	
v  Dust	loadings	could	be	higher	offshore	as	the	dust	is	transported	in	the	Saharan	Air	Layer	(SAL)	at	al>tudes	of	
1500-6000	m	in	boreal	summer.	However,	the	SAL	is	at	lower	al>tudes	in	boreal	winter,	so	this	hypothesis	
seems	unlikely		
v  We	used	low	volume	samplers	(~	1	m3	air	filtered	h-1),	[5]	&	[6]	used	high	volume	samplers	(~	1	m3	min-1).	Low	
volume	samplers	require	longer	sampling	dura>ons	in	order	to	collect	sufficient	material	on	the	filters.	This	
would	manifest	as	a	reduc>on	in	the	concentra>on	of	Al	per	air	volume	filtered	per	>me	unit,	due	to	the	longer	
run	>mes	
v  We	were	sampling	from	specific	sectors	
Results	&	Discussion	
(2)	PMF	output:	factor	fingerprint	of	aerosol	sources	
Ø  Used	for	aerosol	source	appor>onment	
Ø  Mineral	dust		
Ø  =	red,	other	factors	do	not	necessarily	represent	the	same	
source,	but	an	aaempt	has	been	made	to	colour-code	them	
based	on	similar	groupings	of	elements	
Ø  Smallest	contribu>on	from	mineral	dust	in	Agadir,	greatest	in	
Dakhla		
Ø  Some	TEs	have	liale	to	no	mineral	dust	source:	
Ø  Agadir:	V,	Ni,	Zn,	Mo,	Pb	
Ø  Laayoune	:	P,	Mo,	Cd,	Pb	
Ø  Dakhla	:	P,	Ni,	Mo,	Cd,	Pb	
Ø  P	is	an	interes>ng	case.	We	tend	to	think	of	P	as	being	
derived	from	mineral	dust.	However,	contribu>on	of	mineral	
dust	to	aerosol	P	was	low.	P	could	be	a	special	case	in	this	
region	due	to	the	presence	of	open	cast	P	mines	(Morocco	is								
														second	largest	exporter	of	P	in	the	world)	
				(3)	RelaRonship	between	dust	events	&	elemental	raRos	
o  Al	is	a	proxy	for	mineral	dust		
o  Dust	events	(peaks	in	Al	concentra>on)	have	liale	effect	on	the	mass	ra>o	of	lithogenic	elements	to	Al	
(e.g.	Ti/Al),	sugges>ng	mineral	dust	is	main	source	of	these	elements	
o  Dust	events	reduce	the	ra>o	of	anthropogenic	elements	to	Al	(e.g.	Cd),	sugges>ng	these	elements	have	
lower	rela>ve	abundances	in	mineral	dust	than	industrial	emissions	
o  On	low	dust	days	(low	Al)	there	were	peaks	in	ra>o	of	anthropogenic	elements	to	Al	
				(4)	Enrichment	Factors	
q  Normalised	to	Al	
q  Only	enrichment	>	10	
considered	significant	(marked	
by	horizontal	line)	
q  Lithogenic	elements	not	significantly	enriched	(top	row)	
q  Generally	highest	enrichment	in	Agadir	samples	
q  P	most	enriched	in	Laayoune	samples	
q  Cd	enriched	at	all	loca>ons	but…	
q  Cd/Al	(mass/mass)	at	all	
sta>ons	(Agadir	=	2.1x10-5	-	
2.7x10-4;	Laayoune	=	8.4x10-6	
-	2.9x10-4;	Dakhla	=	3.0x10-6	-	
2.0x10-4)	fall	close	to	the	
range	observed	at	nearby	
					loca>ons	(e.g.,	Cap	Spartel	=	4.6x10-5	-	2.3x10-4	[8]	&	Gran	Canaria	=	4.6x10-5	–	1.84x10-4	[5]		
q  Same	trend	seen	for	other	anthropogenic	TEs,	e.g.	Pb/Al																
Pumps	
Weather	vane	
Aerosol	sampler	 Filter	holder	
Filter	holder	
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A case study of aerosol trace element deposition to Moroccan coastal waters [Poster]

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A case study of aerosol trace element deposition to Moroccan coastal waters

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