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LAMMA AND ELECTRON MICROPROBE ANALYSIS OF ATMOSPHERIC AEROSOLS
F. Bruynseels, H. Storms, R. van Grieken
To cite this version:
F. Bruynseels, H. Storms, R. van Grieken. LAMMA AND ELECTRON MICROPROBE ANALYSIS OF ATMOSPHERIC AEROSOLS. Journal de Physique Colloques, 1984, 45 (C2), pp.C2-785-C2-788.
�10.1051/jphyscol:19842180�. �jpa-00223855�
LAMMA AND ELECTRON MICROPROBE A N A L Y S I S OF ATMOSPHERIC AEROSOLS F. Bruynseels, H. Storms and R. Van Grieken
Department of Chemistry, University of Antwerp (UIA), B-2610 FliZrijk, Be Zgium
Resume - Une microsonde LAMMA, e t une sonde e l e c t r o n i q u e automatis6e avec detecteurs de rayons-X, o n t & t @ u t i l i s e e s pour e t u d i e r l a composition elementaire, l a s p e c i a t i o n inorganique e t l a morphologie de p a r t i c u l e s atmosph&riques, 6chantillonnees & p l u s i e u r s e n d r o i t s c a r a c t e r e maritime ou c o n t i n e n t a l , p o l l u e ou n a t u r e l .
A b s t r a c t - A l a s e r microprobe mass analyser and a h i g h l y automated e l e c t r o n probe X-ray microanalysis u n i t have been used t o study t h e elemental com- p o s i t i o n , i n o r g a n i c s p e c i a t i o n and morphology o f atmospheric aerosols c o l - l e c t e d a t various remote t o p o l l u t e d and marine t o c o n t i n e n t a l l o c a t i o n s
The l i t e r a t u r e on s i n g l e p a r t i c l e a n a l y s i s o f atmospheric aerosols, and p a r t i c u l a r l y of remote aerosols, i s s t i l l very scarce. Yet microscopic a n a l y s i s can g i v e valuable i n f o r m a t i o n about t h e sources, the generation mechanisms and t h e t r a n s p o r t o f natural and p o l l u t i o n aerosols, and thus be h e l p f u l i n e v a l u a t i n g t h e impact o f long-range t r a n s p o r t o f anthropogenic substances on a g l o b a l scale, e s t i m a t i n g t h e p o s s i b l e e f f e c t s on t h e e a r t h ' s c l i m a t e , assessing the d e p o s i t i o n o f e o l i a n t e r r e s t r i a l ma- t e r i a l and o f a i r p o l l u t a n t s i n t o the ocean and t h e t r a n s f e r o f p a r t i c u l a t e m a t t e r from sea t o a i r .
I n an e f f o r t t o c h a r a c t e r i z e the composition o f t h e n a t u r a l aerosol b a s e l i n e and t o study the t r a n s f o r m a t i o n processes o f p o l l u t e d aerosols, we have examined numerous aerosol samples from remote d e s e r t and j u n g l e a i r and from various remote t o p o l l u t e d coastal environments using 1 aser microprobe mass a n a l y s i s (LAMMA) and/or by using e l e c t r o n probe X-ray m i c r o a n a l y s i s (EPXMA) w i t h f a c i 1 i t i e s f o r automatical 1 y recogni- z i n g and s i z i n g p a r t i c l e s .
EXPERIMENTAL Analysis techniques
Laser Microprobe Mass Analysis was performed w i t h t h e LAMM@~OO instrument (Leybold Heraeus, Koln, F.R.G.). The pulsed l a s e r l i g h t ( A = 265 nm -r = 15 ns o f a f r e - 1
quency quadrupled neodymium-YAG Laser (power d e n s i t y o f 1016-1011 W/cm ) i s focussed o n t o t h e sample through an o p t i c a l microscope ( m a g n i f i c a t i o n s o f 10 x t o 1250 x) w i t h t h e a i d o f t h e r e d spot o f a continous He-Ne l a s e r beam, t h a t f o l l o w s t h e same o p t i - c a l path as the h i g h power l a s e r . Depending on t h e l a s e r i n t e n s i t y which can be a t - tenuated t o 1 % of f u l l power by means o f a 25-step o p t i c a l f i l t e r sequence, t h e sample i s more o r l e s s damaged o r even perfora5ed ( l a t e r a l
The working pressure o f t h e instrument i s <10 mbar. The accelerated i n t o a t i m e - o f - f l i g h t mass spectrometer, t h a t storage, mass c a l i b r a t i o n and i n t e g r a t i o n .
t h e p o s i t i v e o r negative i o n mode. The ions are detected
e l e c t r o n m u l t i p l i e r , and t h e s i g n a l s are f e d i n t o a D i g i t a l Minc-11 computer f o r LAMMA o f f e r s f a s t , multi-element analyses w i t h a d e t e c t i o n l i m i t around I ppm, and gives i n o r g a n i c s p e c i a t i o n and organic f i n g e r p r i n t i n f o r m a t i o n on a micrometer scale, b u t the s p a t i a l r e s o l u t i o n i s l i m i t e d t o 1 pm, the q u a l i t y o f t h e l i g h t - m i c r o s c o p i c viewing i s poor, t h e technique i s d e s t r u c t i v e and q u a n t i f i c a t i o n i s s t i l l d o u b t f u l because m a t r i x e f f e c t s and thermodynamic n o n - e q u i l i b r i u m c o n d i t i o n s p l a y an important r o l e i n l a s e r induced molecular i o n formation. A v e r y i n t e r e s t i n g f e a t u r e i s t h a t ,
Article published online by EDP Sciences and available at http://dx.doi.org/10.1051/jphyscol:19842180
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when a l o w l a s e r power o f about 0.2 p J i s a p p l i e d t o p a r t i c l e s l a r g e r t h a n 1 pm, LAMMA can be used i n t h e " l a s e r d e s o r p t i o n mode" so t h a t o n l y t h e s u r f a c e m a t e r i a l o f a p a r t i c l e i s evaporated and i o n i z e d , and subsequent l a y e r s o f one p a r t i c l e can be assessed.
The E l ectron-Mi croprobe was a JEOL JXA-733 instrument,equipped w i t h secondary e l e c t r o n and b a c k s c a t t e r d e t e c t o r s and w i t h b o t h energy- and w a v e l e n g t h - d i s p e r s i v e X-ray d e t e c t i o n systems. The e n e r g y - d i s p e r s i v e s p e c t r a were e i t h e r processed d i r e c t l y b y a LSI-11/23 computer o r o f f - l i n e b y a VAX 11/780 mainframe computer. The TRACOR PRC-program ( " P a r t i c l e R e c o g n i t i o n and C h a r a c t e r i z a t i o n " ) was a v a i l a b l e : i t a l l o w s a u t o m a t i c d e t e c t i o n o f p a r t i c l e s , subsequent s i z i n g and q u a l i t a t i v e a n a l y s i s . The program has been expanded r e c e n t l y t o a l l o w q u a n t i t a t i v e a n a l y s i s o f p a r t i c l e s i n an automated way /2/.
EPXMA e x h i b i t s d e t e c t i o n l i m i t s t h a t a r e some 1000 t i m e s l e s s advantageous t h a n LAMMA, b u t i t a l l o w s a reasonable accuracy and a h i g h degree o f automation, d e t a i l e d morphology i n f o r m a t i o n i s obtained, up t o a dozen elements can be assessed s i m u l t a n e - o u s l y and mapping o f t h e elemental d i s t r i b u t i o n w i t h i n a v i e w i n g f i e l d i s p o s s i b l e by X-ray mapping.
Sampling method
Atmospheric a e r o s o l p a r t i c l e s were c o l l e c t e d i n a l l cases by means o f b a t t e r y o r mains powered pumps and f i v e - s t a g e s i n g l e - o r i f i c e B a t t e l l e t y p e cascade impactors, operated a t a f l o w r a t e o f 1 l / m i n . The aerodynamic c u t - o f f diameters f o r t h e d i f - f e r e n t stages were >4 pm, 4-2 pm, 2-1 pm, 1-0.5 pm and 0.5-0.25 pm f o r t h e stages 1 t o 5, r e s p e c t i v e l y . For LAMMA t h e p a r t i c l e s were c o l l e c t e d on 100 nm t h i c k f o i l o f Formvar supported b y 300 mesh e l e c t r o n microscope g r i d s which a r e mounted on M y l a r backings. The sampling t i m e was r e s t r i c t e d t o t e n minutes t o a v o i d o v e r l o a - d i n g and t h e r e s u l t i n g p a r t i c l e - p a r t i c l e i n t e r a c t i o n s . F o r EMPA t h e same t a r g e t s can be used, o r Nuclepore was used as a b a c k i n g s u b s t r a t e .
Sampling s i t e s
The a v a i l a b l e samples o f a i r p a r t i c u l a t e m a t e r i a l had been c o l l e c t e d a t s e v e r a l l o c a t i o n s :
x o n - a s a i l b o a t t r a c k across t h e c e n t r a l A t l a n t i c and E a s t e r n P a c i f i c Oceans /3,4/
and a t remote i s l a n d s i t e s i n t h e c e n t r a l P a c i f i c x a t a remote s i t e i n t h e Namib d e s e r t /5/
rn a t a remote s i t e i n t h e Amazon j u n g l e /6/
x a t v a r i o u s remote t o p o l l u t e d c o a s t a l s i t e s i n Pernambuco, B r a s i l /7/
x on a t r a n s s e c t f r o m a remote c o a s t a l s i t e t h r o u g h a h e a v i l y p o l l u t e d i n d u s t r i a l area i n Bahia, B r a s i l
x a t s e v e r a l l o c a t i o n s i n Western Europe.
SUMMARIZED RESULTS
The LAMMA-data f o r some o f t h e sampling s i t e s l e d t o t h e f o l l o w i n g o b s e r v a t i o n s : x on l a r g e p a r t i c l e - s i z e p u r e l y marine a e r o s o l s , o n l y s i g n a l s from t h e expected m a j o r seawater i o n s and t h e i r c l u s t e r compounds can be detected, e.g. Na+, Mg+, K+, Na2 + , Na20+, N ~ ~ O H + , Na(NaCl)+, K(NaCl)+, K(KCl)+, Na(NaC1)2+, Na2S03+, K(NaC1)2+, N ~ ~ S O ~ , K N ~ ~ S O ~ , ~ a ( ~ a ~ 1 ) ; , 0-, OH-, CN-, S-, C1-, SO-, SO;, SO; ,(NaCl)Cl-, HSOi , N ~ ~ S O ~ , e t c . No d i r e c t evidence o f t r a c e metal enrichment d u r i n g ocean- atmosphere t r a n s f e r i s found /8/.
x i t i s p o s s i b l e t o i d e n t i f y s u l f u r compounds i n m i c r o m e t r i c p a r t i c l e s and t o d i s - t i n g u i s h e.g. between Na SO4, Na SO3 and Na2S203. The n e g a t i v e i o n mode s p e c t r a a r e dominated by SOn ions; t 2 e i r patDern w ~ t h r e s p e c t t o t h e fragment valence can be modelled b u t i t i s i d e n t i c a l f o r t h e t h r e e compounds and does n o t a l l o w i d e n t i f i c a - t i o n . T h i s i s a l s o t r u e f o r t h e Na 0; $ l u s t e r s i n t h e p o s i t i v e i o n mode s p e c t r a . The r a t i o o f t h e s t r o n g N ~ ~ S O ' and ?(a 50 mass peaks, which i s n o t c r i t i c a l l y a f - f e c t e d by t h e l a s e r power, doss o f f e r 3 ';the p o s s i b i l i t y o f unambiguous i d e n t i f i - c a t i o n t h a t can be c o n f i r m e d v i a t h e Na3S and Na2S02 i n t e n s i t i e s /9/.
x i n a l l examined l a r g e atmospheri c a e r o s o l p a r t i c l e s , s u l f u r i s p r e s e n t as s u l f a t e , x i n s m a l l e r p a r t i c l e s , an excess S i s always found and i t i s e n r i c h e d a t t h e s u r - face, as was e v i d e n t f r o m subsequent shots a t l o w l a s e r power. The S-excess i n - creases w i t h i n c r e a s i n g anthropogenic c h a r a c t e r o f t h e environment. The mass peaks
rn i n p u r e l y marine s e a s a l t p a r t i c l e s i n t h e size-range o f 1-2 um, a c o a t i n g w i t h NaN03 was discovered, probably formed by a heterogeneous gas phase/salt p a r t i c l e i n t e r a c t i o n . The number o f these NaN03 coated p a r t i c l e s increases and t h e i r s i z e range widens w i t h i n c r e a s i n g p o l l u t i o n character.
x w i t h i n c r e a s i n g d i s t a n c e i n l a n d from the sea, t e r r e s t r i a l i n d i c a t o r s such as posi- t i v e i o n s from V, T i , Fe and Pb and n e g a t i v e i o n s such as SiO; become more predomi- nant, as w e l l as negative i o n species i n d i c a t i v e o f hydrocarbons.
x i n a h e a v i l y p o l l u t e d i n d u s t r i a l area w i t h petrochemical, f e r t i l i z e r and i n d u s t r i - a l p l a n t s some 30 km downwind from t h e ocean, n o t l e s s than 8 d i s t i n c t aerosol types can be d i s t i n g u i s h e d by LAMMA
- i n the l a r g e size-ranges:
( 1 ) sea s a l t p a r t i c l e s
( 2 ) sea s a l t p a r t i c l e s w i t h NaN03 coat
- i n t h e small s i z e ranges:
(3) HS04 r i c h p a r t i c l e s w i t h organic backbone fragmentation (Cn-) ,
( 4 ) NH4 , Na, Ca, V, F e - r i c h p a r t i c l e s
( 5 ) Na, Mg, Al, S i , Ca, T i , Fe, Ba, S r - r i c h p a r t i c l e s
( 6 ) p a r t i c l e s c o n t a i n i n g HSO, and NO, anions and the organic backbone fragmentation
p a t t e r n -r I I
( 7 ) p a r t i c l e s c o n t a i n i n g phosphorus and n i t r o g e n anions (PO- and NO-) ( 8 ) p a r t i c l e s w i t h NH: , Na, K, V, Fe and mass peaks a t m/zn= 30, 8g, 88.
The r e s u l t s o f EPXMA and t h e corresponding secondary e l e c t r o n p i c t u r e s showed t h e f o l l o w i n g / l o / :
x l a r g e p a r t i c l e marine aerosols are cubic i n shape, as expected f o r ha1 i t e , and c o n t a i n t h e major seawater-el ements,
x unexpected complications such as p i l e - u p o f l a r g e s e a s a l t p a r t i c l e s i n t h e sam- p l i n g device can a r i s e under t h e sampling c o n d i t i o n s used r o u t i n e l y i n combination w i t h PIXE-analysis, i m p l y i n g d i f f e r e n t i a l r e c r y s t a l l i s a t i o n o f seawater according
t o t h e Van ' t H o f f scheme a f t e r the sampling step, and l e a d i n g t o erroneous m a t r i x c o r r e c t i o n s i n t h e PIXE-technique
x l a r g e p a r t i c l e c o n t i n e n t a l aerosols c o n t a i n m a i n l y A l , Si, Mg, Ca and Fe as detec- t a b l e elements.
x t h e q u a n t i f i c a t i o n procedures commercially a v a i l a b l e i n EPXMA-software are n o t adequate f o r accurate a n a l y s i s f o r p a r t i c l e s w i t h v a r i a b l e shape.
gubmicrometer p a r t i c l e s , a t a l l the examined sampling s i t e s , both remote and p o l l u - ted, marine and c o n t i n e n t a l , a r e predominantly s p h e r i c a l , suggesting condensation from t h e gas phase as a source process, and they c o n t a i n o n l y S (and sometimes some Na, C1 and Ca) as d e t e c t a b l e elements, w i t h most o f t h e mass made up by low-Z e l e - ments l i k e N and 0. This i s probably i n d i c a t i v e f o r NH4HS04, (NH4)2S04 and/
o r organic S-compounds formed from n a t u r a l o r p o l l u t i o n S-compounds. I n areas w i t h r i c h vegetation, K occurs concomitantly w i t h S i n the small spherical p a r t i c l e s , and t h i s may be due t o n a t u r a l o r anthropogenic v e g e t a t i o n f i r e s .
x a t p o l l u t e d c o n t i n e n t a l s i t e s , S and Si are o f t e n detected simultaneously i n small s p h e r i c a l p a r t i c l e s .
I t i s hoped t h a t combining b e t t e r t h e LAMMA- and EPXMA-data and analysing more r e - mote and p o l l u t e d samples w i l l g i v e a c l u e t o t h e o r i g i n o f t h e v a r i o u s p a r t i c l e types.
REFERENCES
1- Sessions o f LAMMA Symposium h e l d i n Dusseldorf, F.R. Germany, Oct. 8-10, 1980 (Organizers HILLENKAMP F., KAUFMANN R.), Z. Anal. Chem., 308 (1981) 193.
2- VAN DYCK P., STORMS H., VAN GRIEKEN R., t h i s volume
3- MAENHAUT W., SELEN A., VAN ESPEN P., VAN GRIEKEN R., WINCHESTER J.W., Nucl. I n s t r . Meth. 181 (1981) 399.
4- MAENHAUT w., R A E M D O ~ H., SELEN A., VAN GRIEKEN R., WINCHESTER J.w., J. Geoph. Res. 88 (1983) 535.
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