Assessment of pollution aerosols sources above the Straits of Dover using lead isotope geochemistry

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Assessment of pollution aerosols sources above the Straits of Dover using lead isotope geochemistry
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  Ž . The Science of the Total Environment 236 1999 57  74  Assessment of pollution aerosols sources above theStraits of Dover using lead isotope geochemistry Karine Deboudt a,  , Pascal Flament a , Dominique Weis b ,Jean-Paul Mennessier b , Patricia Maquinghen a a ( )Uni    ersite du Littoral-Cote d’Opale, LISE-ELICO UPRES-A CNRS 8013 , BP 59, F-62930 Wimereux, France ´ ˆ b Uni    ersite Libre de Bruxelles, Departement Sciences de la Terre et de l’En   ironnement, CP 160  02, B-1050 Brussels, ´ ´  Belgium Received 15 February 1999; accepted 8 June 1999  Abstract We assess the capability of lead isotopes to study the transport of pollution aerosols above the Straits of Dover bycollecting atmospheric aerosols above the Eastern Channel and the Southern Bight of the North Sea. During thesame period, we characterized the lead isotopic signature of the main industrial sources on the French coast near theStraits of Dover. Urban and automobile-derived aerosols were also collected. Due to the phasing out of lead in Ž 206 207 . gasoline, the urban isotopic composition Pb   Pb  1.158  0.003 has become more radiogenic, although it is Ž highly variable. On a regional scale, major industrial emissions have a well-defined isotopic composition 1.13  206 207 . Ž  206 207 . Pb   Pb  1.22 , more radiogenic than the petrol-lead signature 1.06   Pb   Pb  1.12 . These resultstogether with those measured near the main coastal highway show that the automobile source has become a minorcomponent of particulate lead in air. On a local scale, Dunkerque, the most urbanized and industrialized area alongthe Straits of Dover, may transiently control elevated lead concentrations. Except for the occurrence of local andregional range transport episodes, lead concentrations in the Straits of Dover can be related to remote orsemi-remote pollution source emissions. Combining air mass retrospective trajectories and related lead abundancesand isotopic compositions, it can be shown that lead aerosols srcinating from eastern Europe have an isotopic Ž  206 207 . signature 1.145   Pb   Pb  1.169 different from the isotopic composition of west-European lead aerosols Ž  206 207 . 1.111   Pb   Pb  1.142 . The influence of remote North American sources is suggested, with caution, due touncertainties in meteorological calculations.    1999 Elsevier Science B.V. All rights reserved.  Keywords:  Aerosols; Atmospheric transport; Lead isotopes; European lead sources  Corresponding author.0048-9697  99  $ - see front matter    1999 Elsevier Science B.V. All rights reserved. Ž . PII: S 0 0 4 8 - 9 6 9 7 9 9 0 0 2 8 6 - 7  ( ) K. Deboudt et al.  The Science of the Total En   ironment 236 1999 57   74 58 1. Introduction The use of lead isotopic compositions to assessthe relative impact of various anthropogenicsources in the distribution of lead abundance in Ž the marine troposphere is now common Maringet al., 1987; Hamelin et al., 1989; Veron et al., ´ . 1992; Veron and Church, 1997 . As other heavy ´ metals, such as zinc, are typically associated withthis element, lead is considered as a tracer for Ž metallic pollution aerosols Nriagu and Pacyna, . 1988; Kersten et al., 1992; Buat-Menard, 1993 . ´ The association of atmospheric lead with submi-cronic particles leads to long-range transport over Ž oceanic areas within a few days Settle and Pat- . terson, 1982; Patterson and Settle, 1987 , whichallows the tracing of the dispersion of pollution Ž aerosols over great distances Duce et al., 1991; . Rosman et al., 1993 .Impact studies were supported, since the 1980s Ž Petit et al., 1984; Sturges and Barrie, 1987, 1989; . Hopper et al., 1991; Mukai et al., 1993 , by the well-defined isotopic composition of automobileemissions, the major source of lead in the am- Ž . bient air Pacyna et al., 1984; Nriagu, 1990 . How-ever, since 1975 in the United States and themid-1980s in Europe, legislative measures havebeen passed to reduce and eventually to eliminatelead in gasoline. As a consequence of this phas-ing-out, the abundance of lead in the troposphere Ž . has decreased Nriagu, 1990 , but this elementremains essentially anthropogenic in atmosphericaerosols. Numerous studies have shown that thisreduction is discernible on a global scale Ž Eisenreich et al., 1986; Page et al., 1988; Boutronet al., 1991, 1994; Rosman et al., 1993; Groussetet al., 1994; Loranger and Zayed, 1994; Migon etal., 1994; Nicolas et al., 1994; Flament et al., . 1996 . Thus, it is now important to take intoaccount other sources than automobile emissions Ž lead smelters, ferrous and non-ferrous metalmanufacturing plants, fossil fuel combustion, .  waste incinerators, etc. in studies discriminating Ž pollution aerosol srcins Nicholson and Branson, . 1993; Pacyna, 1995; Aberg et al., 1999 , especially Ž . at a regional scale Monna et al., 1995 .The aim of our study in the Straits of Dover,surrounded by significant industrial areas Ž . London, Anvers, Dunkerque , is twofold. Ž . 1 To provide isotopic signatures of industriallead sources and compare them to automobileemissions signatures. To estimate the potentialimpact of a given source, these atmospheric data will be complemented with the mass-size distribu-tion of emitted lead. Ž . 2 To assess how lead isotopic geochemistrycan trace the transport of those aerosols in thestudied marine zone. The preceding 4 days retro-spective air-mass trajectories, ending at 950 hPa Ž . a few hundred meters above sea level , for eachsampling experiment, allow us to locate the po-tential emitters and to consider the relative im-pact of regional sources vs. the long-range influ-ence of the main anthropogenic emissions areas,particularly in Europe. The lead contents of at-mospheric aerosols above the studied marine area Ž . the Straits of Dover are variable and depend onthe srcin of the collected air masses, which sug-gests numerous possible influences by local or Ž . more distant sources Bertho et al., 1998 . Ourstudy aims at constraining these sources. For thisassessment, potential emissaries are categorizedunder four levels:   local sources located on the French coast of the Straits of Dover;   regional sources corresponding with emitterslocated in northern France;   semi-remote sources involving medium-rangetransport episodes from north-western Europe Ž . Great Britain or Benelux ; and   remote sources involving long-range transportepisodes from central and eastern Europe orfrom overseas. 2. Experimental  2.1. Sampling  Size-fractionated atmospheric aerosols havebeen collected above the Straits of Dover, off  Ž . Dunkerque and Boulogne sur Mer Fig. 1 . The    (    )  K  .D e  b   o u d   t   e  t   a l    .    T  h   e  S  c  i    e  n c  e  o  f    t   h   e T  o t   a l   E  n     i   r  o n m e  n t  2   3   6  1   9   9   9   5   7     7  4    5    9    Table 1 Ž . Isotopic compositions of lead aerosols collected above the Straits of Dover for granulometric class es corresponding to higher lead concentrations a b 206 204 206 207 208 206   Sample identification Sampling Wind Wind Pb WAD Granulometric class Pb   Pb Pb   Pb Pb   Pb  3 Ž . Ž . Ž . Ž . Ž . zone direction speed ng m   m for isotopic   0.003   0.003   0.003  1 Ž . Ž . location    m s composition  Eastern Channel samples 25 April 1995 50  49  1  32   270  20 3  5 24 0.63 0.33  0.64 18.178 1.165 2.082 Ž . 4 May 1995 1 50  46  1  32   70  160 3 70 0.85 0.33  0.64 18.320 1.169 2.088 Ž . 4 May 1995 2 50  46  1  32   70  160 3 70 0.85 0.64  1.04 18.060 1.157 2.0994 September 1995 50  48  1  27   260  280 5 30 0.6 0.33  0.64 17.378 1.117 2.1436 November 1995 50  49  1  33   180  200 4 17 0.68 0.64  1.04 17.870 1.145 2.115 Southern Bight samples Ž . 10 March 1995 1 51  05  2  14   120  130 10 123 0.87 0.33  0.64 17.560 1.111 2.137 Ž . 10 March 1995 2 51  05  2  14   120  130 10 123 0.87 0.64  1.04 17.383 1.111 2.13530 May 1995 51  05  2  04   290  300 6 13 1.42 2.1  5.08 17.662 1.134 2.121 Ž . 15 September 1995 1 51  05  2  00   180  200 4 17 0.71 1.04  2.1 17.866 1.141 2.120 Ž . 15 September 1995 2 51  05  2  00   180  200 4 17 0.71 0.64  1.04 17.775 1.142 2.120 Ž . 11 October 1995 1 51  03  2  13   140  150 3 85 1.76 1.04  2.1 17.815 1.142 2.111 Ž . 11 October 1995 2 51  03  2  13   140  150 3 85 1.76 0.33  0.64 17.700 1.132 2.124 Ž . 11 October 1995 3 51  03  2  13   140  150 3 85 1.76 2.1  5.08 17.750 1.126 2.127 a    Ž . Pb is the total lead concentration in air sum of all granulometric stages . b WAD is the weighted average diameter of particles containing lead.  ( ) K. Deboudt et al.  The Science of the Total En   ironment 236 1999 57   74 60 Ž . sampling device cascade impactor was mountedat the top of an 8-m mast, on the  R.V. Sepia II  ,approximately 2 m in the front of the vessel and 6m above sea level. To avoid contamination fromthe smokestack of the ship, the sampling wasinterrupted when the wind direction became per-pendicular to the vessel. For this, the electricpump was controlled by a weathercock. The sam-pling zones were located between the sailing railof the Straits and the coast, in order to avoidcontamination from large ships which sail in theStraits. Continental winds occurred for all sam-plings, except for the 30 May 1995, 25 April 1995 Ž . and 4 September 1995 see Table 1 for whichcontamination from ships cannot be discarded.The main urban and industrial sources of aero-sols on the French coast of the Straits of Dover were sampled by cascade impaction or by bulk Ž . filtration cellulose filters . The same mast, with-out weathercock, was mounted at approximately100 m from the considered industrial source, onthe lee side. Aerosols were collected in the centerof the town for urban sources. Sampling sites arereported in Fig. 1. The preparation of cascadeimpactors and bulk filters for sampling are de- Ž . scribed in Flament et al. 1996 .  2.2. Analysis Quantitative analysis of lead was performed,after acid digestion, by graphite furnace atomic Ž . absorption spectrometry GFAAS as described in Ž . Flament et al. 1996 , for bulk filters and for eachgranulometric class of the cascade impactor fil- Ž ters. The average analytical blank acid digestion .   1 of an acid washed filter is 200 ng g of filter.This contamination lead represents less than 5%of the average lead concentration of the samplefilters. These last results permit us to compute,for each cascade impactor sampling, the ‘weighted Ž . average diameter’ WAD of the aerosols contain-ing lead. Fig. 1. Location map of the sampling sites for this study, around the Straits of Dover.    (    )  K  .D e  b   o u d   t   e  t   a l    .    T  h   e  S  c  i    e  n c  e  o  f    t   h   e T  o t   a l   E  n     i   r  o n m e  n t  2   3   6  1   9   9   9   5   7     7  4    6   1    Ž Fig. 2. Isotopic compositions of lead aerosols above the Straits of Dover for this study black symbols: Eastern Channel samples; grey symbols: Southern Bight . Ž . samples . Asterisks are medians of European lead isotopic compositions and bars are 95% confidence limits on the medians Hopper et al., 1991 .
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