Seasonal variation of particulate lipophilic organic compounds at

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  • Seasonal variation of particulate lipophilic organic compounds at

    nonurban sites in Europe

    T. S. Oliveira,1 C. A. Pio,1 C. A. Alves,1 A. J. D. Silvestre,2 M. Evtyugina,1 J. V. Afonso,1

    P. Fialho,3 M. Legrand,4 H. Puxbaum,5 and A. Gelencser6

    Received 4 February 2007; revised 11 June 2007; accepted 27 June 2007; published 5 September 2007.

    [1] Atmospheric aerosol samples, collected continuously during a sampling period longerthan 1 year at six rural and background sites representing oceanic, rural and continentalenvironments across Europe, were extracted, fractionated and analyzed by gaschromatography/mass spectrometry. The detailed organic speciation of the aerosolsamples enabled the choice of some key compounds to assess the contribution of differentsources. Lipophilic molecular markers were identified, including vehicle exhaustconstituents, meat smoke tracers, phytosterols of higher photosynthetic plants and woodsmoke components, especially from coniferous vegetation. The lowest concentrationsand a quasi absence of seasonal cycle were observed at the oceanic background site ofAzores. The highest values and a greater number of compounds were registered at the twocontinental lower-level sites. Aveiro (a rural site close to the small coastal Portuguesecity of Aveiro) and K-puszta (Hungarian plains) both presented a seasonal variationwith winter maxima attributable to a sizable contribution of wood-burning and meat-cooking sources. At the mountain sites (Puy de Dome, Schauinsland and the high alpinesummit of Sonnblick), concentrations maximized during summer as a result of thedecoupling of the lower layers from the midtroposphere with wintry weather and theinfluence of boundary layer air masses during the warm season.

    Citation: Oliveira, T. S., C. A. Pio, C. A. Alves, A. J. D. Silvestre, M. Evtyugina, J. V. Afonso, P. Fialho, M. Legrand, H. Puxbaum,

    and A. Gelencser (2007), Seasonal variation of particulate lipophilic organic compounds at nonurban sites in Europe, J. Geophys. Res.,

    112, D23S09, doi:10.1029/2007JD008504.

    1. Introduction

    [2] Aerosol particles are ubiquitous components of theatmosphere and include inorganic substances such as sul-fates and carbonaceous species, which are divided intoorganic carbon (OC) and elemental carbon (EC). Theincreasing consciousness of the impact of atmosphericparticles on climate, and the incompletely recognized butserious effects of anthropogenic aerosols on air quality andhuman health, motivated numerous scientific studies. Thosestudies have shown that particulate phase organic com-pounds could account for 2050% of the atmosphericaerosol mass [Guo et al., 2003; Pio et al., 2001a]. Deter-mining the sources of carbon-containing aerosols has been

    hampered by the complex nature of these materials and by apoor knowledge of the transformation processes that takeplace in the particle phase. The great number of samplesnecessary to trace contributions from specific emissionsources makes such an investigation costly and time con-suming. Thus most studies to date, aiming at a detailedcharacterization of organic aerosols, rely on the implemen-tation of brief field experiments. Even studies of seasonalevaluation are usually based on two independent short-termsampling campaigns, performed during both summer andwinter representative periods.[3] Some studies have focused on the assessment of

    natural versus anthropogenic contributions to the carbona-ceous aerosol by searching molecular markers or tracers,which include organic compounds that are source specific,react slowly in the atmosphere, and do not partition to thegas phase during the transport [e.g., Schauer et al., 1996;Schauer and Cass, 2000; Simoneit, 1989, 1999, 2002;Zheng et al., 2002; Simoneit et al., 2004; Leithead et al.,2006; Li et al., 2006; Subramanian et al., 2006; Wang et al.,2007]. These studies indicate that biomass and fossil fuelcombustion supply high loads of molecular markers toorganic aerosols. However, in spite of the considerablework that has been done in the organic characterization ofspecific source emissions (motor vehicle exhaust, food-cooking operations, fireplace combustion of wood, etc.),studies focused on the differences in the molecular compo-

    JOURNAL OF GEOPHYSICAL RESEARCH, VOL. 112, D23S09, doi:10.1029/2007JD008504, 2007ClickHere

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    1Centre for Environmental and Marine Studies and Department ofEnvironment, University of Aveiro, Aveiro, Portugal.

    2Centre for Research in Ceramics and Composite Materials andDepartment of Chemistry, University of Aveiro, Aveiro, Portugal.

    3Department of Agrarian Sciences, University of Azores, Angra doHerosmo, Portugal.

    4Laboratoire de Glaciologie et Geophysique de lEnvironnement,Centre National de la Recherche Scientifique, Saint Martin dHeres, France.

    5Institute for Chemical Technologies and Analytics, Technical Uni-versity of Vienna, Vienna, Austria.

    6Air Chemistry Group at the Hungarian Academy of Sciences,University of Pannonia, Veszprem, Hungary.

    D23S09 1 of 20

    http://dx.doi.org/10.1029/2007JD008504

  • sition to infer the diverse contributions to the ambientaerosol were essentially conducted in regions impacted bybiomass burning or in metropolitan areas very influenced bytraffic. Long-term studies of lipophilic organic markers inatmospheric aerosols of more pristine environments arestill scarce. Moreover, the relative contribution of naturalversus anthropogenic sources is not fully known and hencethe extent to which the fragile natural equilibrium of theatmosphere has been disturbed is scantily understood.The establishment of a comprehensive aerosol data set,lacking till now, for various environmental conditions inEurope (marine/continental, rural/urban, boundary layer/free troposphere, and winter/summer) will contribute to(1) improve emission inventories, (2) develop climatemodels, (3) establish source/receptor relationships thatgovern the individual compounds present in the breathablecomplex organic mixtures and, (4) consider environmentalpolicies foreseeing possible emission control strategies.[4] This work presents a year-round study of lipophilic

    particulate organic compounds at different nonurban siteslocated along a west-east transect in Europe, from theAzores to Hungary, crossing highly elevated Alpine sites.It should be stressed that measurements were taken withoutinterruption and under very hard conditions in certainlocations, such as a cliff in a remote island in the middleof the North Atlantic Ocean, or the top of a permanentlyfrozen Alpine mountain. The seasonal variation of particle-associated homologous compound sequences, specific lipo-philic organic tracers and diagnostic parameters were ana-lyzed to establish a chemical fingerprint of emission sourcescontributing to atmospheric aerosols on a continental scale.This investigation represents, as far as we know, the mostextensive temporal and spatial study of the detailed consti-tution of atmospheric lipophilic organic aerosols acrossseasons of nonurban Europe, the free troposphere, or thecentral Atlantic region.

    2. Experimental Section

    [5] Integrated in the EU Project CARBOSOL, high-volume samplers were used, from July 2002 to September2003, to collect atmospheric particulate matter on preheatedquartz fiber filters. The sampling sites are listed in Table 1.These sites provide a west-east transect across Europe goingfrom the middle of the Atlantic Ocean to the plains ofeastern Europe. The detailed characterization of the sam-pling sites and a map showing their locations could befound in a companion paper [Pio et al., 2007]. At four sitesvery similar size cuts of 22.5 mm were used and theaerosol fraction collected was quite similar. At the other twolocations, the available equipment capable of resolving

    problems of sampling in subfreezing conditions impliedthat PM10 samples had to be collected. Collection ofPM10, instead of PM2.5, in the two mountain sampling sitesof SIL and PDD may influence the values obtained forcompounds present predominantly in coarse particles orig-inated from sources such as dust from soil origin, althoughat these high altitudes this is presumed to be a far lessserious interference than it would be at lowland dustierenvironments. A size distribution study carried out withdifferent types of air masses at PDD have showed that,except during a sporadic Saharan dust event, the organicaerosol mass is chiefly present below 3 mm [Sellegri et al.,2003]. To collect an adequate amount of material forperforming all CARBOSOL analysis, even at remote oce-anic and mountain sites, weekly sampling was carried out inorder to guarantee masses of the target compounds higherthan the detection limits of the analytical procedures.Because of the extended sampling period, volatilization/condensation processes for semivolatile organics may haveoccurred. Also, oxidation of filter-deposited organics bystrong oxidants, such as ozone, may have happened duringsampling. Measured concentrations for oxygenated organicspecies represent therefore an upper limit of the trueatmospheric levels [Pio et al., 2001b]. It can, however,been assumed that, during sampling, equilibrium betweengas and particulate phase would govern the behavior of thefiltered aerosol similarly to what occurs in the atmosphere.In addition, the large mass of particles collected wouldreduce potential adsorption of semivolatile organic com-pounds on active sites of the quartz fiber surfaces, as resultof their rapid saturation.[6] The weekly aerosol filters collected at the six sites

    were analyzed by a thermal-optical technique to determinethe EC and OC content [Castro et al., 1999; Pio et al.,1994]. On the basis of their organic carbon content, filtersfrom weekly samples were pooled on a monthly basis andwere extracted for 24 hour periods, first w